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Table of contents:

1 Administrative data for the APERTIF project ........................................................................................ 3 1.1 Principle Investigators ..................................................................................................................... 3 1.2 International Science Team............................................................................................................. 3 1.3 Contact Person:............................................................................................................................... 3

2 Executive Summary .............................................................................................................................. 4 3 Some Key Scientific Publications of the Proposers .............................................................................. 5 4 Description of Research Area and Research Plan ............................................................................... 6

4.1 Introduction...................................................................................................................................... 6 4.2 Galaxy Evolution, Cosmology and Dark Energy ............................................................................. 6

4.2.1 Understanding star formation evolution out to z = 1............................................................... 8 4.2.2 The evolving gas content of galaxies ..................................................................................... 9 4.2.3 Probing galaxy evolution in rich clusters .............................................................................. 10 4.2.4 Imaging the low red-shift Cosmic Web ................................................................................. 11 4.2.5 Constraining the Dark Energy Equation of State.................................................................. 13

4.3 The Origin and Evolution of Cosmic Magnetism ........................................................................... 14 4.3.1 The all-sky Rotation Measure grid ........................................................................................ 15

4.4 Pulsars as tools for fundamental physics and astrophysics.......................................................... 16 5 Motivation of Investment Plan ............................................................................................................. 22

5.1 Basic Instrument Designs and Capabilities ................................................................................... 24 6 National Importance and Scientific Accessibility................................................................................. 25 7 International Positioning...................................................................................................................... 26 8 Strategy of the institution with regard to the investment ..................................................................... 27

8.1 Array technology development at ASTRON.................................................................................. 28 8.1.1 Focal Plane Array Research................................................................................................. 29 8.1.2 Aperture Array Research ...................................................................................................... 30 8.1.3 Low cost manufacturing........................................................................................................ 30 8.1.4 LOFAR.................................................................................................................................. 30

8.2 Array technology in APERTIF ....................................................................................................... 31 9 Technical Concept and Budget ........................................................................................................... 32

9.1 APERTIF System Concept............................................................................................................ 32 9.1.1 Antenna array ....................................................................................................................... 33 9.1.2 Digital Beam-forming ............................................................................................................ 33 9.1.3 Correlator System................................................................................................................. 33 9.1.4 Monitoring & Control Software.............................................................................................. 33 9.1.5 Data Handling and Post-processing Software...................................................................... 33 9.1.6 Infrastructure......................................................................................................................... 34

9.2 Project Management ..................................................................................................................... 34 9.3 Budget description......................................................................................................................... 36

10 Exploitation .................................................................................................................................... 37 11 Technical References.................................................................................................................... 38 12 Abbreviation list ............................................................................................................................. 40 13 APPENDIX A: Letters of support................................................................................................... 42

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1 Administrative data for the APERTIF project

1.1 Principle Investigators Robert Braun (ASTRON) Marc Verheijen (Groningen)

1.2 International Science Team Ralph Wijers (Amsterdam) Huib Henrichs (Amsterdam) Lex Kaper (Amsterdam) Ed van den Heuvel (Amsterdam) Rudy Wijnands (Amsterdam) Karel van der Hucht (Amsterdam) Peter Barthel (Groningen) Leon Koopmans (Groningen) Piet van der Kruit (Groningen) Reynier Peletier (Groningen) Marco Spaans (Groningen) Scott Trager (Groningen) Rien van de Weijgaert (Groningen) Saleem Zaroubi (Groningen) Frank Israel (Leiden) Joop Schaye (Leiden) Paul van der Werf (Leiden) Mike Garrett (JIVE) Ger de Bruyn (ASTRON/Groningen)

Heino Falcke (ASTRON) Raffaella Morganti (ASTRON) Tom Oosterloo (ASTRON) Ben Stappers (ASTRON) Lister Staveley-Smith (CSIRO, Australia) Francoise Combes (Paris, France) Rainer Beck (MPIfR, Bonn, Germany) Karl Menten (MPIfR, Bonn, Germany) Uli Klein (Univ. Bonn, Germany) Gabriele Giovannini (Bologna, Italy) Karl-Heinz Mack (Bologna, Italy) Justin Jonas (Rhodes Univ., South Africa) Paul Alexander (Cambridge, UK) Rob Fender (Southampton, UK) Phil Diamond (Manchester, UK) Michael Kramer (Manchester, UK) Peter Wilkinson (Manchester, UK) Steve Rawlings (Oxford, UK)

1.3 Contact Person: Robert Braun Tel: 0521-595254 FAX: 0521-597332 e-mail: braun@astron.nl

Stichting ASTRON Postbus 2 7990 AA Dwingeloo

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2 Executive Summary The Netherlands astronomical community, represented in the top research school NOVA, has chosen to focus its investments in research manpower and observational infrastructure in three areas:

• Formation and evolution of galaxies: from the early Universe to the present • Birth and death of stars: the life cycle of gas and dust • Final stages of stellar evolution: physics of neutron stars and black holes

Unraveling the relevant physics in each of the themes requires observations across a wide frequency range of the electromagnetic spectrum. Hence the community has in recent years invested in radio and advanced digital instrumentation for low (LOFAR), intermediate (WSRT) and high (ALMA) radio frequencies, optical-IR instrumentation for ESO and UK-NL telescopes and for the planned James Webb Space Telescope (MIRI, the Mid-Infrared Instrument), and space instruments for X-rays and gamma-rays. This strategy has proven effective over the years and the Dutch astronomical community consistently receives ratings of ‘Excellent’ in international review evaluations.

Each kind of instrument or facility has a scientifically productive lifetime of up to about a decade before technological advances are required to maintain the momentum of discovery. The current proposal requests finance to enable major advances at intermediate radio frequencies. This frequency range provides unique information on galaxy evolution, cosmology and the distribution of dark matter; on cosmic magnetism and its role in each of the research areas; and on neutron stars and black holes as probes of fundamental physical and astrophysical processes. The most recent investment in this frequency range was in the mid-1990’s and involved upgrading the radio telescope in Westerbork to improve its sensitivity, frequency range and operational flexibility. The current proposal requests funds to dramatically improve the field of view and survey capability in this frequency range.

Over the past decade our community has invested in technical R&D in preparation for the Square Kilometre Array (SKA), a telescope that will revolutionize radio astronomy and that is being planned for construction next decade. The scientific case for the SKA is overwhelming, and has recently been published as a volume of the peer reviewed journal, New Astronomy Reviews, Volume 43, December 2004. The technology to be employed departs from existing telescope designs, which are too expensive to be scaled up as required. Instead of large, movable mechanical antennas, the SKA will employ very large numbers of small antennas connected to powerful computational facilities to create multiple very large telescopes in software. The LOFAR telescope is a pathfinder for SKA – technologically to demonstrate the software telescope concept in an operational environment, and scientifically to explore for the first time at high angular resolution the low frequency radio window on the distant Universe.

The SKA and LOFAR R&D programs have led to a paradigm-shift in radio telescope design. We are now on the threshold of a revolution in performance and discovery space enhancement at intermediate radio frequencies by between one and two orders of magnitude. The means for achieving this remarkable performance gain is the placement of a fully-sampled, low-noise, wide-bandwidth receiver array in the focus of each parabolic dish of a synthesis array instead of the single receiver element that current systems employ. This is comparable to the great performance leap of optical telescope systems in the past decades when they made the transition from a single photometer in the telescope focus to large-format CCD detector arrays.

The great scientific promise of this technology has been recognized simultaneously by three groups around the world, centered in the Netherlands, Australia and South Africa. Each has conceived a similar system design to deploy fully-sampled receiver arrays within the focus of a number of antennas. Our system, “APERture Tile In Focus” (APERTIF), has the lowest total project cost, of 14 M€, by making optimum use of existing mechanical infrastructure, while providing the best scientific performance. We have formed a close collaboration with the other two groups to coordinate system design and provide reciprocal preferred scientific access to all three of the completed facilities. In this way we are: minimizing project costs via joint development, maximizing scientific return to our user community, and initiating access to state-of-the-art radio facilities in both the Northern and Southern Hemispheres in the decade preceding full SKA operations.

The total cost of this work will be 14 M€, of which ASTRON and partners are able to contribute 7 M€. We therefore request from NWO-Groot a subsidy of 7 M€. This funding is earmarked for the construction of fourteen receiver arrays (“tiles”). The partner contributions cover development cost and the construction of the digital correlator needed to combine the signals from the tiles.

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3 Some Key Scientific Publications of the Proposers The Ursa Major Cluster of Galaxies. IV. HI Synthesis Observations Verheijen, M.A.W., Sancisi, R. 2001 A&A 370, 765. The Ursa Major Cluster of Galaxies. V. HI Rotation Curve Shapes and the Tully-Fisher Relations Verheijen, M.A.W., 2001 ApJ 563, 694. The Temperature and Opacity of Atomic Hydrogen in Spiral Galaxies Braun, R., 1997, ApJ 484, 637. The WSRT wide-field HI survey: Local Group Features Braun, R., Thilker, D.A., 2004, A&A 417, 421. On the Continuing Formation of the Andromeda Galaxy: Detection of HI Clouds in the M31 Halo Thilker, D.A., Braun, R., Walterbos, R.A.M., et al. 2004, ApJ, 601, L39.

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4 Description of Research Area and Research Plan

4.1 Introduction In its long term strategic planning our astronomical community has chosen to concentrate its investments to maximize their effectiveness. The three broad research themes selected, their descriptions and research goals may be summarized as follows:

Formation and evolution of galaxies: from high red-shift to the present Galaxies contain billions of stars, as well as interstellar gas and dust, and are embedded in dark halos of unknown constitution. Astronomers are able to look back in time, by observing galaxies at ever greater distances. Because light travels at finite velocity, distant objects are seen at a time when the Universe was young. The expansion of the Universe causes light to be red-shifted, so that the most distant galaxies are those with the highest red-shift. How did galaxies form? What processes have occurred between high red-shift and the present? Do evolved galaxies contain relics which are clues to their formation? What are the influences of the environment, of magnetic fields, of nuclear activity, and of the original large-scale distribution of dark matter? What is the role of massive black holes in galactic nuclei?

Birth and death of stars: the life-cycle of gas and dust New stars continue to be born deep inside molecular clouds in galaxies. The birth process leads to a circum-stellar disk of gas and dust from which planets and comets may subsequently form. What are the physical processes that lead to these new solar systems, and how do they evolve? How is the chemical composition of the gas and dust involving the major biogenic elements modified during the collapse from the cold, tenuous interstellar medium to the dense proto-planetary material? During the late stages of their life, stars inject nucleo-synthetically enriched material into the interstellar medium. How does this material drive the chemical evolution of a galaxy and of the newly-formed stars therein? What drives the mass loss, and how does it influence stellar evolution?

Final stages of stellar evolution: physics of neutron stars and black holes At the end of its life, a massive star explodes and ejects its outer layers. The stellar core collapses to form a neutron star or a black hole. These are the densest objects that exist, and the ones with the strongest gravitational fields. What are the properties of matter at the extreme density in the interior of a neutron star? What are the observational signatures of black holes? Can we observationally verify the extraordinary predictions of General Relativity for the properties of curved space-time near these objects? How do particles and radiation behave near these compact objects? What happens when two compact objects orbiting each other eventually merge? Is this the origin of the most powerful explosions we know, the enigmatic gamma-ray bursts?

Vital information in each of these themes must be acquired at intermediate radio frequencies. The basic system design we are proposing and its capabilities are given in Section 5.1. Examples of specific research projects that the requested investment will make possible are summarized as follows.

4.2 Galaxy Evolution, Cosmology and Dark Energy More and more evidence supports the paradigm of hierarchical galaxy formation, whereby present day galaxies have been built up over cosmological time scales by coalescence of many smaller, less massive systems (e.g. Klypin et al. 1999, Moore et al. 1999). For a particular galaxy this process is described by the so-called merger tree: the accumulation of dark matter mass over time into a final halo. The merger trees are extracted from numerical cosmological simulations and only describe the merging of dark matter halos in a robust manner. However, the role and fate of the gas and stars in this merging process is not well understood due to an incomplete understanding of the relevant physics, the simplicity of the hydrodynamic codes and the limits of numerical resolution. The behavior of the baryons in these merging dark matter halos is often described by semi-analytic techniques (e.g. Kauffman et al. 1993, Baugh et al. 2004). Although many properties of real galaxy populations can be reconstructed in this way, including current star formation rates, luminosity functions, the Tully-Fisher relation and morphological segregation, there are still many open questions that must be answered by better observations:

• When and how quickly did gas settle into dark matter potential wells? • Where, when and how did the gas get converted into stars? • When and how did the merging process of small galaxies develop?

• What is the relative importance of gas accretion versus galaxy merging? • How important is galaxy (trans-) formation today?

Some of these questions will require the sensitivity of the SKA to address effectively, which will permit detection of neutral hydrogen emission out to z > 3 and detection of radio continuum emission from star-forming galaxies out to z ~ 10, but significant progress can already be achieved with the combination of FOV and sensitivity afforded by the APERTIF system. Very large samples (~106) of normal galaxies will be imaged in neutral hydrogen emission out to z = 0.25, while the continuum emission from star-forming galaxies will allow their study out to z ~ 2. These are already long enough look-back times that very substantial changes in the star-formation rate and possibly the gas mass fraction have occurred.

Figure 4.1: The integrated star formation history of the Universe (left) from Heavens et al (2004) as determined from SDSS spectra (filled circles) and a variety of other tracers. Note the dramatic increase from the current epoch out to about z = 0.8, followed by a flattening and possible decline beyond z = 3. The 1.4 GHz radio luminosity plotted against the total infra-red luminosity (right) from Bell (2003). The symbols show various galaxy types, while the solid and dotted lines represent fits to the data. The thick-dashed line shows a model prediction. The radio continuum emission provides an extinction-independent probe of the star formation rate over a range of five orders of magnitude in galaxy luminosity.

Figure 4.2: The resolved radio – FIR correlation in M51. A WSRT 22 cm image is on the left, a Spitzer Space Telescope 70 µm image is in the central panel and the ratio is on the right (from Murphy et al. 2005). A similar degree of variance in the radio-FIR ratio is observed within individual galaxies to what is seen in the global correlation of Figure 4.1. Analysis of this variation is revealing clues to the underlying physical processes and their relevant timescales.

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4.2.1 Understanding star formation evolution out to z = 1

The integrated star-formation history of the universe (the so-called Madau diagram; see Figure 4.1) continues to be determined with greater precision. Star formation rates seem to increase dramatically from the current epoch out to about z = 0.8, then appear to level off and possibly decline beyond z = 3. This tells us how much star formation occurred at a given cosmic epoch, but to understand galaxy evolution we need to know more than this. In particular, where and in what range of environments, did star formation occur at each epoch? Did most stars form in galaxies undergoing “quiescent” star formation, or in galaxies under-going violent star-bursts, and how did this vary with red-shift? How important a role do mergers play in triggering star formation? Do the primary sites of star-formation shift form high mass to low mass galaxies at lower red-shifts (e.g. Cowie et al. 1996)? In the local universe, star formation occurs in a wide range of environments, and with star formation rates ranging over at least five orders of magnitude. As seen in Figure 4.1, radio continuum emission provides a powerful probe of the star-formation activity over this entire range of rates since it correlates exceptionally well with other unbiased tracers of star formation, particularly the FIR emission (e.g. Frick et al. 2001, Garrett 2002, Bell 2003). The physical origins of this correlation are now being subjected to close scrutiny in nearby galaxy disks, as shown in Figure 4.2 (from Murphy et al 2005). Insights are beginning to emerge regarding the critical physical processes and their different lifetimes.

Figure 4.3: The 1.4 GHz luminosity function (left). The symbols show an observational estimate for local star forming galaxies from Sadler et al. (2002). The lines show model predictions for z=0 (solid), 0.5 (dotted), 1 (dashed) and 2 (long dashed) from Baugh et al. (2004). Detailed modeling of the observed distributions is permitting predictions to be made of what deeper surveys will detect. The predicted red-shift distribution (right) of normal star forming galaxies at 1.4 GHz for a sample reaching a depth of 16 µJy taken from Baugh et al. (2004). The lines represent total (solid), bursts (dashed) and quiescent (dotted) star formation. Note that the median red-shift of such a deep survey is likely to be z ~ 1, with a tail extending out beyond z = 3. Understanding the where and why of star formation in different environments will be a goal of deep, wide-field continuum surveys with the APERTIF system. This system will permit continuum imaging with 7-14 µJy/beam rms over a 15000 square degree FOV (about twice that of the Sloan Digital Sky Survey (SDSS) coverage) in a 3 year survey. Such a sensitivity level corresponds to the measured confusion limit at GHz frequencies with the anticipated beam size. This is almost two orders of magnitude deeper than the VLA NVSS survey (that reaches 450 µJy/beam rms). Image quality in the APERTIF survey will be superior (about three times more sensitive) than the WSRT image of M51 shown in Figure 4.2 for all of the nearby galaxy disks in the survey coverage. As shown by the simulated luminosity functions and red-shift distributions in Figure 4.3 (from Baugh et al. 2004), such a deep APERTIF survey is predicted to reach a median red-shift of about unity, with an extended tail in the distribution extending beyond z ~ 3. The region of spatial overlap with the SDSS will provide high quality optical identifications as well as spectroscopic red-shifts for a sub-set of detections. In this way it will be possible to determine exactly what types of galaxies (low or high mass, bursting or quiescent) are responsible for the growth of stellar mass with cosmic time and how star formation rates are affected by the large scale environment.

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Figure 4.4: The mass density of HI (left) expressed in units of the present day critical density as function of red-shift. Model predictions from Baugh et al (2004) are shown by the solid line. Note the strong evolution in the gas mass density with red-shift, but the very sparse observational constraints which are now available. The HI mass function (right) with data points from Zwaan et al (2003) and model predictions from Baugh et al (2004) at red-shift 0 (solid), 1 (dotted), 3 (dashed) and 4 (dot-dashed). Detailed modeling of the observed local distributions is permitting predictions to be made of what will be detected in deeper surveys.

Figure 4.5: HI emission from a galaxy within Abell 2192 at z=0.1887. The upper panels show individual HI channel maps, while the bottom panels show (left to right): integrated HI contours overlaid on an optical image, channel map contours overlaid on the optical image and finally an Hα velocity field obtained with the PMAS IFU (from Verheijen 2004). Deep integrations with the APERTIF system will permit comparable HI kinematic imaging of large galaxy samples out to z ~ 0.25 simultaneously, since the FOV encompasses 8 square degrees (corresponding to 1560 Mpc2 at z = 0.19).

4.2.2 The evolving gas content of galaxies

Various lines of evidence suggest that there is strong evolution of the neutral gas content in galaxies, perhaps even between red-shifts of only a few tenths and the present. This is implied by both the evolution in star-formation rate, by almost an order of magnitude, between 0 and 0.2 seen in Figure 4.1 as well as the comparable decline in the mass density of neutral hydrogen shown in Figure 4.4. In the case of the mass density it is currently far from clear when and where this transition takes place. The only strong observational constraints are at red-shifts near zero from surveys of HI emission (Zwaan et al. 2003) and at red-shifts greater than about 2 from damped Lyα studies (e.g. Giavalisco et al. 2004). The

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model curves in Figure 4.4 correspond to the semi-analytic models of Baugh et al. (2004). Although much of the red-shift range will require the much higher physical sensitivity of the SKA to address, the low red-shift portion of the distribution, out to about z = 0.25 can be determined by large area surveys with APERTIF. The same 3 year duration survey, referred to in Section 4.2.1 to image a 15000 degree2 FOV to a 7-14 µJy/beam radio continuum rms over 300 MHz bandwidth will simultaneously provide a spectral line sensitivity of 185 µJy/beam over 430 kHz (corresponding to about 100 km/s); which is more than a factor of 30 higher sensitivity than the recently completed HIPASS survey (Barnes et al. 2001). The upper end of the HI mass function (at 5x1010 MSun for Ho = 71 km/s) can then be detected at 5σ out to z = 0.35, while an MHI* galaxy (with 7x109 MSun) can still be detected at 5σ to z = 0.14. This database will permit a deep unbiased search for HI absorption toward, and associated with, some 107 AGN brighter than a few mJy in the survey region (e.g. Morganti et al. 2005). Deeper integrations (of several hundred hours) will be made in selected regions, to permit the type of kinematic imaging shown in Figure 4.5 to be carried out over regions of 8 degree2 (corresponding to 1560 Mpc2) simultaneously. In contrast, the deep VLA integration shown in Figure 4.5 by Verheijen (2004) sampled a FOV of only 62 Mpc2. Deep, wide-field surveys will enable the first inroads to be made on documenting the evolution of gas content over the past 3 Gyr.

Figure 4.6: Examples of HI morphologies of nearby galaxies in Cluster environments. The left panels show HI filaments near S0 galaxies in Ursa Major, most likely caused by tidal interactions. The right panel shows the effect of ram-pressure stripping in Virgo (from Kenney et al. 2004).

4.2.3 Probing galaxy evolution in rich clusters

Rich clusters of galaxies, in relation to the large scale structure in which they are embedded, offer a unique laboratory to study the effects of global and local environments on the properties of their constituent galaxies. Evidence has accumulated that this environment affects both the star formation rate and morphology of galaxies, resulting in the well known morphology-density relation in the local universe (e.g. Dressler 1980). The ratio of lenticular to spiral galaxies in clusters decreases with red-shift (e.g. Dressler et al 1997), while the fraction of blue members in cluster cores increases with red-shift between z = 0 and 0.4 (Butcher & Oemler 1984). Furthermore, the star formation rate is observed to decrease with increasing galaxy density, both in the outer parts of distant clusters (e.g. Abraham et al 1996), and more locally in the recent SLOAN survey (Gomez et al 2003). The nature and timescale of the physical mechanisms that are responsible for the observed environmental dependencies and the evolutionary processes remain largely unclear. Ideally, to study these processes, one would like to probe the evolution of galaxies as they travel from the low density filaments to the dense cluster cores, sampling a variety of environments over a range of red-shifts, including galaxy clusters in different dynamical states and of different richness classes. Optically this work has been pioneered by Abraham et al (1996) and more recently by Balogh et al (1999) and Treu et al (2003). Happily, observing the distribution and kinematics of the cold gas in galaxies provides one of the most direct windows on the physical processes involved, and adds to these optical studies in a crucial way:

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1) Blind, volume limited HI surveys provide an optically unbiased probe of all the gas-rich galaxies in the entire volume. Galaxies of low surface brightness and faint dwarf galaxies which are relatively gas-rich, are easily detected in HI surveys. Figure 4.6 shows some results of an extensive, albeit not blind, HI survey with the WSRT of the nearby Ursa Major volume (Verheijen & Sancisi 2001) in which several gas-rich galaxies were discovered. HI surveys have also revealed the HI deficiencies of galaxies in cluster cores.

2) Observations of the 21cm emission line of HI naturally provide red-shifts which reveal any spatial and velocity clustering of gas-rich galaxies. It directly maps the substructure in filaments and clusters, and helps to unravel the dynamical state of galaxy groups and clusters (e.g. Bravo-Alfaro et al. 2000). For instance, if a sub-clump of galaxies is observed to be gas-rich, it is quite unlikely it has crossed the high density cluster core on its infall trajectory.

3) The presence of cold gas in galaxies is a prerequisite for star formation, and the amount and distribution of cold gas regulate the duration and intensity of star formation periods. The accretion and removal of this cold gas reservoir is a crucial element in the process that transforms galaxies, and is directly related to the evolutionary state of a galaxy's stellar population. HI observations allow us to compare optical probes of enhanced, decreased and halted star formation with the cold gas reservoir.

4) The response of the cold HI in the outer disks of galaxies is the most sensitive and obvious tracer of galaxy-galaxy interactions and some examples are illustrated in Figure 4.6. In many cases, tidal interactions and the fate of the cold gas reservoir can only be witnessed in HI images.

5) The morphology of the HI distribution can critically distinguish between ICM-ISM interactions like ram-pressure and viscous stripping (e.g. Schulz & Struck 2001; Abadi et al 1999), and gravitational disturbances like galaxy harassment (e.g. Moore et al. 1996). The effect of ram-pressure stripping is also illustrated in Figure 4.6. In such a case, where the cold gas is in the process of being removed from the plane of an infalling galaxy, the spatial and kinematic offset of the gas may indicate the speed and direction in which a galaxy is moving, and thus help to reconstruct its orbit.

6) HI surveys also provide deep radio continuum images. These are particularly useful as an independent estimate for the star formation rate, complementary to optical probes. Unlike optical methods, even dust enshrouded starbursts can be detected.

HI surveys of clusters in the local universe (z = 0 to z = 0.08) are currently being extended out to red-shifts of 0.2 where signs of cosmological evolution have been detected optically and the Butcher-Oemler effect has become noticeable. The motivation is not only to study the mechanisms mentioned above, but also to study what exactly causes the Butcher-Oemler phenomenon. In particular, it is necessary to distinguish whether it is the gaseous properties of the infalling galaxies that are different at z = 0.2 or whether there are other mechanisms at work that enhance star formation at those red-shifts. Deep integrations are being obtained with the Westerbork telescope to survey the environment of the two galaxy clusters, Abell 963 and 2192. Some 20 galaxy detections have already been made in and around these z = 0.2 clusters. While this is a painstaking process with current instrumentation, demanding 100’s of hours of integration for only 0.4 deg2 of instantaneous sky coverage, the field will be revolutionized with the wide-field capabilities of APERTIF, since survey speed will increase by at least a factor of 25 (or more for band-width limited applications).

4.2.4 Imaging the low red-shift Cosmic Web

Extragalactic astronomy has traditionally focused on the regions of extreme cosmic over-density that we know as galaxies. Only in recent years has the realization emerged that galaxies do not dominate the universal baryon budget but are merely the brightest pearls of an underlying Cosmic Web. Filamentary components extending between the massive galaxies are a conspicuous prediction of high resolution numerical models of structure formation (e.g. Davé et al. 1999, 2001). Such calculations suggest that in the current epoch, cosmic baryons are almost equally distributed by mass amongst three components: (1) galactic concentrations, (2) a warm-hot intergalactic medium (WHIM) and (3) a diffuse intergalactic medium. These three components are each coupled to a decreasing range of baryonic over-density: log(ρH/<ρH>) > 3.5, 1 – 3.5, and < 1 and are probed by QSO absorption lines with specific ranges of neutral column density: log(NHI) > 18, 14 – 18, and < 14, as shown in Figure 4.7. The neutral fraction is thought to decrease with decreasing column density from about 1% at log(NHI) = 17, to less than 0.1% at log(NHI) = 13. Although a very wide range of physical conditions can be found within galaxies, the WHIM

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is thought to be a condensed shock-heated phase of galaxy interaction debris with temperature in the range 105 – 107 K, while the diffuse IGM is predominantly photo-ionized with temperature near 104 K. A complicating factor to this simple picture is the growing suspicion that the gas accretion process, traced by the log(NHI) = 14 – 18 systems, may well occur in two rather different regimes (e.g. Binney 2004, Keres et al. 2004). Low to moderate mass galaxies (MVir < 1012 MSun) may experience primarily “cold-mode'' accretion (T ~ 104.5 K) along filaments, while only more massive systems may be dominated by the more isotropic “hot-mode'' accretion (T ~ 105.5 K), which until recently was thought to be universal (e.g. Rees & Ostriker 1977, Davé et al. 2001).

WHIM LLS

Lyα−forest

Figure 4.7: The red-shift evolution of over-dense regions (left) in a numerical simulation showing the increasing mass fraction with time of gas in the range log(T) = 4.5 – 7, the so-called Warm-Hot Intergalactic Medium (from Davé et al .1999). Also shown are the regimes of Damped Lyα, Lyman Limit system and Lyα forest absorber systems. A Cosmic Web filament (center) of HI gas connecting the nearby galaxies M31 and M33 together with the corresponding HI distribution function (left) from Braun & Thilker (2004). The curves are the HI data, while the filled points represent QSO optical absorption line data. With sensitive HI observations the Lyman Limit absorption systems can be directly imaged in emission, despite their small neutral fraction, permitting direct study of the Warm-Hot Intergalactic Medium and it’s large reservoir of baryons. The strongest observational constraints on the cosmic web come from the statistics of the QSO absorption lines. Enough of such QSO spectra have been obtained to allow good statistical determinations to be made of the rate of occurrence of intervening absorbers as function of their column density. By binning such data in red-shift intervals, it has even been possible to gauge the cosmic evolution of intervening absorbers (e.g. Storrie-Lombardi 2000). Inter-galactic space has apparently become continuously tidier by about an order of magnitude from red-shifts of several down to zero; with a decreasing cross-section of high column absorbers. At the current epoch we can now confidently predict that in going down from HI column densities of 1019 cm-2 (which define the current “edges'' of well-studied nearby galaxies in HI emission) to 1017 cm-2, the surface area will increase by a factor of 30. The critical observational challenge is crossing the “HI desert'', the range of log(NHI) from about 19.5 down to 18, over which photo-ionization by the intergalactic radiation field produces an exponential decline in the neutral fraction from essentially unity down to a few percent (e.g. Dove & Shull 1994). Nature is kinder again to the HI observer below log(NHI) = 18, where the neutral fraction decreases only very slowly with log(NHI). The baryonic mass traced by this gas (with a 1% or less neutral fraction) is expected to be comparable to that within the galaxies, as noted above. But how are these diffuse systems distributed, what are their kinematics and under what conditions do “cold-mode'' or “hot-mode'' accretion dominate? These are questions which can not be addressed with the QSO absorption line data. The areal density of suitable background sources is far too low to allow “imaging'' of the intervening low column density systems in absorption. Direct detection of the free-free continuum or recombination line emission from the ionized gas has also proven well beyond the capabilities of current X-ray and optical instrumentation. For example the expected Hα emission measure is only about EM = 5x10-4 cm-6 pc. The very best current Hα imaging results reach down to about EM = 0.1 cm-6 pc, which is still orders of magnitude removed from what would be needed. Although conventional imaging in the 21cm emission line of neutral hydrogen has not typically reached column densities below about 1019 cm-2, this is not a fundamental limitation. Long integrations with an (almost-) filled aperture can achieve the required brightness sensitivity to permit direct imaging of the small neutral fraction within the Cosmic Web filaments between galaxies. The first detection of such diffuse filaments in the extended environment of M31 has just been made by Braun & Thilker (2004). This

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was accomplished by utilizing total power measurements made with the fourteen 25m dishes of the WSRT. Although the angular resolution is low (49 arcmin corresponding to 11 kpc at the M31 distance) the column density sensitivity is very high (4x1016 cm-2 rms over 17 km/s). A diffuse filament is detected connecting the systemic velocities of M31 to M33 (at a projected separation of 200 kpc) and also extending away from M31 in the anti-M33 direction as shown in Figure 4.7. This diffuse filament appears to be fueling denser gaseous streams and filaments in the outskirts of both galaxies. Peak neutral column densities within the filament only amount to some 3x1017 cm-2. The interaction zone of the diffuse filament with M31 has been studied in complimentary surveys that permit calculation of the HI distribution function from HI emission measurements (rather than QSO absorption measurements) over an unprecedented range in log(NHI) = 17.2 to log(NHI) = 21.9 as shown in Figure 4.7. The HI distribution function of these structures agrees very well with that of the low red-shift QSO absorption lines which are also plotted in the figure as filled circles with error bars. The predicted factor of 30 increase in surface covering factor for low NHI emission has been observationally verified. In so doing, it has been possible to provide the first image of a Lyman Limit absorption system. The morphology and kinematics are fully in keeping with the cosmic web hypothesis outlined above. We are now in a position to witness the continuing gaseous fuelling of normal galaxies with direct imaging. Efforts are now underway to extend the study of Lyman Limit Systems in HI emission beyond the Local Group. The deepest practical survey at this time (involving more than 1000 hours of WSRT observing time) will reach an rms of 2x1017 cm-2 rms over 20 km/s within a 35x3 arcmin beam. This should permit the environments of several hundred galaxies to be probed to these depths for the first time. This should permit some of the brightest Cosmic Web filaments to be studied, when they fortuitously align with the elongated beam. A similar survey with the APERTIF system will reach at least 5 times deeper in the same observing time, permitting the wide-spread kinematic study of diffuse filaments as faint as the M31/M33 system at distances of 10 Mpc or larger.

Figure 4.8: Predicted galaxy power spectrum (left) before and after filtering of the smooth component (top and bottom) and displaying the characteristic imprint of acoustic oscillations. The oscillations are best traced by mass concentrations which are still in the linear regime, k < kmax, which shifts to smaller k as z goes to zero. The relative error obtained in w, the ratio of Dark Energy pressure to energy density (right) as a function of sample size and survey volume (adapted from Blake and Glazebrook 2003). A large-scale APERTIF survey can contribute substantially to our understanding of Dark Energy.

4.2.5 Constraining the Dark Energy Equation of State

Over the past few years we have entered an “era of precision cosmology” in which rough estimates of many key cosmological parameters have been replaced by what can reasonably be described as measurements. Remarkable progress in observations of the Cosmic Microwave Background (CMB) has been central to this transformation (e.g. Spergel et al. 2003). The current standard cosmological (ΛCDM) model assumes that the Universe is composed of baryons, dark matter and some form of dark energy. The nature and properties of this last component in particular form some of the most pressing cosmological questions.

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The power spectrum of galaxies on large scales (> 30 Mpc) should contain a series of small-amplitude acoustic oscillations of identical physical origin to those seen in the CMB. These features result from oscillations of the photon-baryon fluid before recombination and encode a characteristic scale – the sound horizon at recombination – which has been accurately determined by CMB observations to be 144 +/- 4 Mpc (Spergel et al. 2003). This scale can be used as a standard ruler (Eisenstein 2002). It’s recovery from a galaxy red-shift survey depends on the assumed cosmological parameters, particularly the dark energy model, and thus refines that model over a range of red-shifts (e.g. Blake and Glazebrook 2003). The application of this cosmological test does not depend on the overall shape of the power spectrum, which can be divided out using a smooth fit, but only on the residual oscillatory nature of the acoustic peaks. Hence the method is insensitive to smooth broad-band tilts in P(k) induced by such effects as a running spectral index, red-shift-space distortions, and complex bias schemes. It would be very surprising if the biasing scheme introduced oscillatory features in k-space liable to obscure the distinctive acoustic peaks and troughs. However, it is important to remain In the linear regime (k < kmax(z)) , where non-linear growth, peculiar velocity and galaxy bias are minimized. The predicted galaxy power spectra, both before and after filtering, together with kmax at a series of red-shifts are illustrated in Figure 4.8. In the absence of major systematic effects, constraints on the dark energy model are limited almost entirely by how much cosmic volume one can survey. The relative precision in a determination of the dark energy equation-of-state w(z) = P/ρ is shown in the right-hand panel of Figure 4.8 as a function of sample size and survey volume (from Blake and Glazebrook 2003). Both survey attributes are critical to maximize, since not only shot-noise but cosmic variance may dominate. Survey volume in the figure is normalized to that of the Sloan Digital Sky Survey (about 2x108 h-3 Mpc3). The recent Sloan Luminous Red Galaxy sample determination (Eisenstein et al. 2005) and expected Sloan main survey result are indicated on the plot, as well as three possible future determinations. The APERTIF point is based on the 3 year radio continuum / HI line survey that has been referred to several times already in this Section. More than 106 HI detections are predicted from this survey (utilizing the Zwaan et al. 2003 HIMF) out to a maximum red-shift of about 0.35, and probing a volume of about 4x108 h-3 Mpc3. This represents a major improvement over the Sloan results, but is still far from ideal. Since the median red-shift of a wide-field APERTIF survey will be below 0.2, this determination will only give clean sampling of the first peak and dip of the galaxy power spectrum. Although no concrete plans have yet been developed, it is possible that a dedicated 8m class optical telescope will be equipped to address this problem during the coming decade with surveys covering several hundred square degrees. The SKA determination, with an expected red-shift coverage of 0.5 – 1.5 will be truly ground-breaking, by permitting an accurate determination of a possible red-shift dependence of w back to look-back times of 10 Gyr.

4.3 The Origin and Evolution of Cosmic Magnetism Understanding the Universe is impossible without understanding magnetic fields. They fill intra-cluster space, affect the evolution of galaxies and galaxy clusters, contribute significantly to the total pressure of interstellar gas, are essential for the onset of star formation and control the density and distribution of cosmic rays in the ISM. But in spite of their importance, the evolution, structure and origin of magnetic fields are still open problems in fundamental physics and astrophysics. Specifically, we still do not know how magnetic fields are generated and maintained, how magnetic fields evolve as galaxies evolve, what the strength and structure of the magnetic field of the intergalactic medium might be, or whether fields in galaxies and clusters are primordial or generated at later epochs. Most of what we know about astrophysical magnetic fields comes via the detection of radio emission. Synchrotron emission measures the total field strength, while its polarization yields the orientation of the ordered field in the plane of the sky as well as the degree of field ordering as illustrated in Figure 4.9. A measurement of Faraday rotation of the polarization plane due to an intervening magneto-ionic medium yields the rotation measure, RM = ∫( neB)dl, for that medium. The recently developed Faraday Rotation Measure Synthesis methodology (Brentjens & De Bruyn 2005) can be used to optimally recover even multiple RM components along the line-of-sight by employing a large number of spectral channels over a

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significant fractonal bandwidth as illustrated in Figure 4.9. Even very weak and extended polarized emission can be detected reliably in this way, as shown in Figure 4.10 for emission from the Perseus Cluster observed with the WSRT from 310 to 390 MHz with 156 kHz sampling (De Bruyn & Brentjens 2005).

Figure 4.9: The magnetic field orientation in the grand design spiral M51 (left). Radio continuum contours are overlaid on an HST image, with vectors superposed showing the field orientation (from Fletcher et al. 2004). Radio polarimetry is the premier tool for studying the magnetic field strength and geometry in astrophysical sources. The Rotation Measure Transfer Function and the RM Synthesis spectrum (right) toward the pulsar PSR J0218+4232. This illustrates the excellent RM resolution and low RM side-lobe level that can be obtained with a combination of good frequency sampling and moderate fractional bandwidth (from De Bruyn 2005) such as will be provided by the APERTIF system.

Figure 4.10: Total intensity (left) and polarized intensity (center) at a Rotation Measure of 52 rad m-2 arising within the Perseus Cluster as observed with the WSRT at 310 – 390 MHz (from De Bruyn & Brentjens 2005). The RM synthesis method permits reliable detection of even such diffuse magnetic plasma within a galaxy cluster. The distribution of extragalactic source counts (right) at 1.4 GHz in both total intensity (solid lines) and polarized intensity (dashed lines) as a function of the limiting survey flux density (from Beck & Gaensler 2004). Wide-field APERTIF surveys will detect some 1x106 compact polarized sources with a spacing on the sky of only 9 arcmin, allowing extensive characterization of the magnetic fields permeating intervening structures in the universe.

4.3.1 The all-sky Rotation Measure grid

Currently some 1200 extragalactic sources and ~300 Galactic pulsars have measured RMs. These data have proved useful probes of magnetic fields in the Milky Way, in nearby galaxies, in clusters and in distant Lyα absorbers. However, the sampling of such measurements over the sky is very sparse and most measurements are at high Galactic latitude. A major step forward in understanding the origin and evolution of magnetic fields will follow from achieving a deep wide-field RM survey. The same 3 year APERTIF survey already referred to in the preceding sub-sections, reaching a 7-14 µJy rms over 15000 deg2 in Stokes I, will enable thermal noise

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limited RM measurement from a large fraction of the ~20000 radio pulsars in the Galaxy which are beamed toward us (see Figure 4.11 below and Cordes et al., 2004) as well as some 1x106 compact polarized extragalactic sources with an angular spacing on the sky of only about 9 arcmin, as can be seen in the right hand panel of Figure 4.10 (from Beck and Gaensler 2004). In our Galaxy, the large sample of pulsar RMs obtained with APERTIF, combined with distance estimates from parallax of from their dispersion measures, can be inverted to yield a complete delineation of the magnetic field in the spiral arms and disk on scales ≥ 100 pc. Small-scale structure and turbulence can be probed using Faraday tomography, in which foreground ionized gas produces complicated frequency dependent Faraday features when viewed against the diffuse Galactic polarized radio emission (e.g. Haverkorm et al. 2003). Magnetic field geometries in the Galactic halo and outer parts of the disk can be studied using the extragalactic RM grid. In clusters of galaxies, magnetic fields play a critical role in regulating heat conduction, and may also both govern and trace cluster formation and evolution. Estimates of the overall magnetic field strength come from the inverse Compton detections in X-rays, from detections of diffuse synchrotron emission, from cold fronts and from simulations. The only direct measurements of field strengths and geometries come from RMs of background sources (e.g. Feretti & Johnston-Hollitt, 2004). Currently only 1 – 5 such RM measurements can be made per cluster (e.g. Govoni et al. 2001). Only by considering an ensemble of RMs averaged over many systems can a crude picture of cluster magnetic field structures be established (e.g. Clarke et al. 2001). With the APERTIF RM grid, the polarized background source density will already be increased by about an order of magnitude (to ~50 deg2), making it possible to study many individual clusters. Deeper polarimetric observations of selected fields will permit a further order of magnitude increase in the sampling density, making it possible to derive a detailed map of the field in each cluster. With such information, careful comparison with other cluster attributes such as the presence of cooling flows, recent merger activity and X-ray morphology should allow the role of the field to be understood in the broader context of cluster evolution. Since many of the sources making up the RM grid are likely to be quasars showing foreground Lyα absorption (of varying HI column density), it may well be possible to build up a large enough sample to detect a trend of RM with red-shift within these intervening absorption systems. This experiment has been attempted several times with existing data sets, but only a relatively small number of absorbing systems show a clear excess in RM. These data provide only marginal (if any) evidence for evolution of RM with red-shift (e.g. Oren & Wolfe 1995). The various limitations of these previous studies can all be circumvented with the APERTIF sample. The Galactic foreground contribution to each source RM, which has added an uncertainty as large as ∆RM ~20 – 30 rad m-2 to previous determinations, will be modeled with a 1000 times higher source density. The overriding limitation to the previous studies has been the very limited number of available sources per red-shift bin. By correlating the APERTIF RMs with the SDSS, a vast increase in the sample size is expected, so that different evolutionary models for RM with red-shift should be clearly distinguished.

4.4 Pulsars as tools for fundamental physics and astrophysics Pulsars are of great utility, no matter where they are found, since they provide so many insights into the local and intervening physical conditions. So far, most known pulsars are Galactic, residing in or near the disk or in globular clusters. Only a small number of radio pulsars are known in the Magellanic Clouds, and none have yet been detected in more distant galaxies. 4.5.1 A Galactic Census of pulsars There are many reasons for undertaking a full census of the pulsar population. The first is that the larger the number of pulsar detections, the more likely it is to find the rare objects that provide the greatest opportunities as physics laboratories. These include; binary pulsars with black-hole companions that can provide strong field tests of gravity; binary pulsars with periods of a few hours or less that can be used for tests of relativistic gravity; milli-second pulsars (MSPs) that can be used as detectors of cosmological gravitational waves; MSPs spinning faster than 1.5 ms, that probe the equation-of-state under extreme

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conditions; hyper-velocity pulsars with translational speeds of 1000 km/s, which probe both core-collapse physics and the gravitational potential of the Galaxy; and objects with unusual spin properties such as discontinuities (“glitches”) and apparent precessional motions.

Figure 4.11: The P – P dot diagram (left) for radio pulsars and magnetars (as of April 2004). Circled points are binary systems, while objects in the upper right part of the diagram have surface magnetic fields exceeding 4.4x1013 G (from Cordes et al. 2004). The detectability of pulsars with the APERTIF system (center) is illustrated with the luminosity – period scatter diagram (adapted from Cordes et al 2004). The horizontal lines correspond to 10σ detection limits with APERTIF for pulsar distances of 10 kpc (lower line) and 100 kpc (upper line). The simulated Galactic pulsar population is shown (right) for an all-sky survey that reaches ~20000 detections (from Cordes et al. 2004). A significant fraction of this number will be accessible with the APERTIF system.

Figure 4.12: Illustration of wide-field pulsar surveys using multiple digital beams on a synthesis array. A pulsar candidate is shown in red in the original (left) and confirming (right) multi-beam observations done with the WSRT array (from Stappers et al. 2005). Multiple digital beams have made it possible to carry out extremely efficient pulsar surveys with wide-field synthesis arrays. The second reason is that a large number of pulsars can be used to delineate the advanced stages of stellar evolution that lead to supernova and compact objects. In particular, with a sufficiently large sample it may be possible to determine the branching ratios for the formation of canonical pulsars and magnetars. It is also possible to estimate the effective birth rates for MSPs and for those binary pulsars that are likely to coalesce on time scales short enough to be of interest as sources of periodic chirped gravitational waves. The third reason for a maximal pulsar sample is its use as a 3-D probe of the interstellar medium. Measurable propagation effects include dispersion, scattering, Faraday rotation and HI absorption which provide line-of-sight integrals of the free-electron-density ne, the fluctuating electron density δne, the product B//ne, and neutral hydrogen density nH. The determination of these observables for a large number of independent sight-lines (of different distances) makes it possible to construct a complete 3-D volumetric map of the Galaxy.

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The nominal, wide-field continuum survey sensitivity of APERTIF, of 7 µJy rms over 300 MHz in a 16 deg2 FOV per day will already permit detection of the vast majority of Galactic pulsars beamed in our direction. This is illustrated in the center panel of Figure 4.11 where the 10σ detection limits at 1.4 GHz are overlaid on the “pseudo luminosity” distribution of all currently detected pulsars (as of April 2004) as function of the pulse period. In making this plot the observed pulsar fluxes have been period-averaged and rescaled (with ν-2) to 1.4 GHz to permit comparison with the nominal continuum sensitivity. The lower line corresponds to an assumed pulsar distance of 10 kpc and the upper line to 100 kpc. The limits shown do not include the loss in sensitivity due to dispersion in the interstellar medium nor scattering which are both distance dependent, however this will only affect the sensitivity at the lowest end of the period distribution and will be no more severe than in previous surveys. Even with only this nominal sensitivity, the majority of the pulsar luminosity distribution lies above the detection limit at 10 kpc, while the high luminosity tail can be detected well beyond 100 kpc. Pulsar surveying with synthesis arrays has historically not been very effective, since the instantaneous sky coverage has typically been restricted to only a single synthesized beam. This situation has finally changed during the past year, with the first successful pulsar surveys using multiple simultaneous digital beams on the WSRT array (Stappers et al. 2005). The multi-beaming approach is particularly effective when the array geometry is periodic, since this permits generation of multiple digital beams with minimal digital electronics. For the case of a regular grating array (such as can be achieved for 12 of the 14 WSRT telescopes) the instantaneous FOV is a repeating series of fan beams which extend across the entire primary beam of the individual telescopes. With only twelve (or N, for an N element grating array) digital beams spaced perpendicular to the fan beam orientation, it is possible to utilize the entire primary beam FOV. The time series toward any synthesized beam within the primary beam can then be reconstructed after the fact by the appropriate linear combination of the eight digital beam outputs that are recorded. The multi-beam pulsar survey mode is illustrated in Figure 4.12 for a small portion of the observed WSRT primary beam response. Each filled ellipse represents a reconstructed synthesized beam that has been searched for pulsar candidates in a two hour integration of a survey field. A second two hour integration obtained 6 months later for the same field is shown on the right, confirming the pulsar candidate seen in the first coverage (shown in red) and providing a high precision position, as well as a period derivative. Digital multi-beaming finally permits efficient wide-field pulsar surveys to be carried out with synthesis arrays. 4.5.2 Deep Pulsar Searches in Globular Clusters Of particular interest will be deep searches for pulsar populations within Globular Clusters, which hold vast reservoirs of MSPs. These are formed at a rate per unit mass which is at least an order of magnitude higher than in the Galactic disk. The reason for this over abundance is thought to be the formation of binaries via two- and three- body encounters in these high stellar density environments. The greatly increased likelihood that many of these MSPs have undergone some form of dynamical interaction means that the chance of finding exotic binaries, such as the long sought MSP-black hole system is perhaps highest in Globular Clusters. Furthermore, the pulsars in each system provide exceptional probes of the history and evolution as well as the present properties; including the dynamics, gas content, accurate distances and proper motion. Moreover, an open question is whether Globular Clusters might contain massive black holes in their centers or possibly even binary black holes. High precision pulsar timing will provide a powerful tool to determine whether such systems are present. This can be achieved either by detecting pulsars in the innermost regions and using their velocities or accelerations to reveal the presence of a black hole, or by using the pulsar population in the cluster as an in situ gravitational wave detector sensitive to the presence of a binary black hole. The high space density of Globular Clusters in the Galactic center region means that the large FOV of the xNTD and KAT systems will dramatically improve the search efficiency for MSPs in such systems.

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Figure 4.13: Transient detection possibilities with the APERTIF system (left) at 1.4 GHz. The limiting source distance is plotted for a 10σ detection within a given integration time. The diagonal lines correspond to the indicated apparent brightness temperature. Incoherent emitters, with TB < 1012K, that vary on second, hour or month timescales will be detectable out to ~100 pc, ~Mpc or ~Gpc distances. Coherent emitters are detectable on correspondingly shorter timescales and out to larger distances. The phase space plot of radio transients (right). The luminosity of specific transient sources and classes of sources is plotted against the product of the emission frequency and the pulse duration (from Cordes et al. 2004). The diagonal lines correspond to the indicated apparent brightness temperatures. Note the observed occurrence of coherent emitters out to TB > 1030K. 4.6 The Dynamic Radio Sky Transient emission – bursts, flares and pulses on time-scales up to about a month – marks compact sources or the locations of explosive or dynamic events. As such, radio transient sources offer insight into a variety of fundamental physical and astrophysical questions including:

• the mechanism of efficient particle acceleration • possible physics beyond the Standard Model • the nature of strong field gravity • the nuclear equation of state • the cosmological star formation history • detecting and probing intervening media.

Searches for radio transients have a long history and a wide range of radio transients are currently known, ranging from extremely nearby (ultrahigh energy cosmic rays impacting the Earth’s atmosphere) to cosmological distances (γ-ray bursts and afterglows). There are also many classes of hypothesized transients. The three critical factors in opening up the transient discovery space to serious study are: instantaneous sensitivity, instantaneous FOV and high time resolution. At high energies (X- and γ-rays), detectors with large solid angle coverage and high time resolution have had great success in finding classes of transient objects. At optical wavelengths there has been recent progress in constructing wide field detectors with high time resolution. Historically, radio telescopes have been able to obtain high time resolution, and this has been paired with an increasing instantaneous sensitivity. The third critical ingredient to enable the study of radio transients, large FOV, will finally become possible with APERTIF at GHz radio frequencies. This provides a critical complement to the low frequency transient sky that will be probed by LOFAR. The higher physical sensitivity of APERTIF (which follows from the much broader bandwidth and lower system temperature) enables APERTIF to reach transient sources which are an order of magnitude fainter than accessible to LOFAR, while the higher observing frequency (by a factor of 10) permits detection of sources which would otherwise still be shrouded by thermal absorption (by a factor of 100). Assuming that the basic emission process is synchrotron radiation, it is possible to estimate the APERTIF detection limits for sources that vary on a particular timescale. The brightness of isotropic synchrotron

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radiation is limited to 1012 K by inverse Compton losses. If relativistic bulk motions are involved, with Lorentz factor, γ, then substantially higher brightness can be realized, which scales with γ3 for a highly aligned viewing geometry. A linear size scale given by c⋅tmin corresponds to an angular size scale θ=c⋅tmin(1+z)/DL, allowing calculation of the apparent brightness temperature associated with a region displaying a flux density variation δS. TB= 3.84x1020 δSJy [λcmDL(Mpc)/(1+z)⋅tmin]2 K The apparent brightness temperatures which have been deduced in this way from the variability timescale of inter-day AGN variables is in the range 1016 – 1021 K (e.g. Quirrenbach et al. 2000). We can invert this expression to predict the flux density variations which can be expected on a particular timescale due to a range of assumed apparent brightness temperatures. In Figure 4.13, we have scaled the 10σ APERTIF sensitivity at 1.4 GHz in a 1 second integration to derive the maximum distance out to which variable sources of a particular apparent brightness temperature can be detected. Isotropic synchrotron transients (TB < 1012 K) out to about 100 pc can be expected to have detectable signatures as short as a few seconds, while highly beamed sources of this type should be detectable from throughout the Galaxy on these timescales. The most likely timescale for detectable transients within nearby galaxies (out to a few Mpc) would seem to be between a few hours (for isotropic emission) down to minutes (for beamed emission). At cosmological distances, the timescale for detectable isotropic transients is about a month (such as for GRB afterglows), while significantly beamed sources might lead to detectable synchrotron transients on hour time-scales. These detection limits are complemented by the transient “phase-space” plot (from Cordes et al. 2004) in the right-hand panel of Figure 4.13, in which similar brightness temperature diagonals are over-plotted on a variety of observed sources in both the incoherent (<1012 K) and coherent (>1012 K) regime. Flare stars and AGN occupy the coherent (lower right) corner of the plot. Beamed synchrotron emission (sometimes modified by Interstellar Scattering (ISS)) applies to observed Inter-day AGN variables (IDVs) and GRBs. Jupiter bursts have comparable brightness temperature, but low intrinsic luminosity. Coherent emission from pulsars, in particular that of giant pulses, extends out to brightness temperatures exceeding 1030 K. Of the many types of likely and possible radio transients (cf. Cordes et al. 2004) we will consider only a few in more detail relating to the early and final stages of stellar evolution: Flare Stars: Radio flares from various active stars and star systems are observed at frequencies of order 1 GHz with flux density levels that can reach about 1 Jy (e.g. Garcia-Sanchez et al. 2003). These systems can show strong polarization, including strong circular polarization. These flares are attributed to particle acceleration from magnetic field activity. Pulsar Giant Pulses: While all pulsars show pulse-to-pulse intensity variations, some pulsars have been found to emit so-called “giant” pulses, pulses with strengths of 100 or even 1000 times the mean pulse intensity. The Crab pulsar was the first pulsar found to exhibit this phenomenon. During one hour of integration the largest measured peak pulse flux of the Crab is roughly 105 Jy at 430 MHz with a duration of roughly 100 µs (Hankins & Rickett 1975), corresponding to an implied brightness temperature of 1031

K. Recently, pulses with ~103 Jy flux and only 2 ns duration of been detected from the Crab at 5 GHz (Hankins et al. 2003). These “nano-giant” pulses imply brightness temperatures of 1038 K, vastly exceeding any other currently known source. For many years, this phenomenon was thought to be peculiar to the Crab pulsar. However, giant pulses have recently been detected from the millisecond pulsars PSR B1821-24 (Romani & Johnston 2001) and PSR B1937+21 (Cognard et al. 1996) and the Crab-like pulsar in the Large Magellanic Cloud, PSR B0540-69 (Johnston & Romani 2003). Transient Pulsars: Kramer et al. (2005) have recently recognized a class of pulsars that produce pulses only a small fraction of the time. In the “on” state they appear indistinguishable from normal pulsars. For example, the 813 ms pulsar, PSR B1931+24 is only detectable about 10% of the time, and the 1.8-s pulsar PSR B0826-34 is in a faint mode (originally thought to be completely extinguished) roughly 70% of the time (Esamdin et al. 2004). Single-pulse searches of the Parkes Multi-beam Pulsar Survey data also have resulted in the discovery of several pulsars whose emission is so sporadic that they are not detectable in standard Fourier domain searches (McLaughlin et al. 2005).

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Radio Supernovae and Gamma-ray Bursts: Supernovae and γ-ray bursts (GRBs) appear to be related since, in at least some cases, they both involve the collapse of a massive stellar progenitor to a neutron star or black hole and the release of ≥ 1051 erg. However the two areas of study may never completely merge since some types of SN (e.g. type Ia) have never been detected in the radio, while some classes of GRB (e.g. the “fast-hard” category) have never been identified in any other wavelength range and are thus supposed to have a different origin than the “slow-soft” GRBs for which some afterglows have been detected. For both SN and GRBs there is a strong incentive to search in the radio for “dark” or “orphan” events. For SN, which are primarily discovered in optical searches, extinction and proximity to the nucleus of a galaxy can lead to many events being hidden from present surveys. For GRBs, the apparent narrowness of the relativistic jet believed to give rise to the γ-ray and X-ray bursts means that most of the events are missed at those wavelengths. The more isotropic radio emission, particularly at later times, should be detectable in sensitive, wide-field searches. As a specific example of the type of pro-active transient observing program that will be carried out with the APERTIF system, we consider the case of a survey for the detection of “orphan” GRBs. The detection frequency of “slow-soft” GRBs from γ-ray monitoring is about one per day. The isotropic radio afterglow from these events has a lifetime of about one month at a peak observed brightness at GHz frequencies of 100 µJy (e.g. Weiler et al. 2004). From relativistic beaming constraints there are expected to be from 10 – 100 GRBs per day which do not happen to be beamed in our direction but which should also give rise to comparable isotropic radio afterglows. Since the APERTIF system will permit continuum imaging to a depth of 20 µJy rms over 160 deg2 in a single days observing, each such coverage is expected to contain about 5 of such detectable “orphans”. Weekly imaging of the same field over a period of a few months will display the appearance and disappearance of the GRB afterglow population. Combined with optical/NIR identification of the GRB host galaxies this will provide an important constraint on massive star formation in the early universe. Scientific References Abadi, M.G., Moore, B., Bower, R.G. 1999, MNRAS 308, 947 Abraham, R.J., Smecker-Hane, T.A., Hutchings, J.B. et al. 1996, ApJ 471, 694 Balogh, M.L.,Morris, S.L., Yee, H.C.K. et al 1999, ApJ 527, 54 Barnes, D.G., Staveley-Smith, L., de Blok, W.J.G. et al. 2001, MNRAS 322, 486 Baugh, C.M., Lacey, C.G., Frenk, C.S., et al. 2004, NewAR 48, 1239 Beck, R., Gaensler, B.M., 2004, NewAR 48, 1289 Bell, E.F., 2003, ApJ 586, 794 Binney, J., 2004, MNRAS 347, 421 Blake, C.A., Glazebrook, K., 2003, ApJ 594, 665 Braun, R., Thilker, D.A., 2004, A&A 417, 421 Bravo-Alfaro, H., Cayette, V., van Gorkom, J.H., Balkowski, C. 2000, AJ 119, 580 Brentjens, M.A., De Bruyn, A.G., 2005, A&A in press, astro-ph/0507349 Butcher, H., Oemler, A., 1984, ApJ 285, 426 Clarke, T.E., Kronberg, P.P., Böhringer, H., 2001, ApJ 547, L111 Cognard, I., Shrauner, J.A., Taylor, J.H., Thorsett, S.E., 1996, ApJ 457, L81 Cordes, J.M., Lazio, T.J.W., McLaughlin, M.A., 2004, NewAR 48, 1459 Cordes, J.M., Kramer, M., Lazio, T.J.W., et al. 2004, NewAR 48, 1413 Cowie, L.L., Songaila, A., Hu, E.M. 1996, AJ 112, 839 Davé, R., Hernquist, L., Katz, N., Weinberg, D.H., 1999, ApJ 511, 521 Davé, R., Cen, R., Ostriker, J.P., 2001, ApJ 552, 473 De Bruyn, A.G., Brentjens, M.A., 2005, A&A in press, astro-ph/0507351 De Bruyn, A.G. 2005, in prep. Dove, J.B., Shull, J.M., 1994, ApJ 423, 196 Dressler, A. 1980, ApJ 236, 351 Dressler, A., Oemler, A., Couch, W.J. et al. 1997, ApJ 490 577 Eisenstein, D.J., 2002, in ASP Conf. Proc. 280, astro-ph/0301623 Eisenstein, D.J., Zehavi, I., Hogg, D.W., et al. 2005, ApJ in press, astro-ph/051171 Esamdin, A., Lyne, A.G., Graham-Smith, F., et al. 2005, MNRAS 356, 59 Feretti, L., Johnston-Hollitt, M., 2004, NewAR 48, 1145 Fletcher, A., Beck, R., et al. 2005, in prep.

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Frick, P., Beck, R., Berkhuijsen, E.M., Patrickeyev, I., 2001, MNRAS 327, 1145 Gaensler, B.M., Beck, R., Feretti, L., 2004, NewAR 48, 1003 Garcia-Sanchez, J., Paredes, J.M., Ribo, M., 2003, A&A 403, 613 Garrett, M.A., 2002, A&A 384, L19 Giavalisco, M., Dickinson, M., Ferguson, H.C., et al. 2004, ApJ 600, L103 Gomez, P.L., Nichol, R.C., Miller, C.J. et al. 2003, ApJ 584, 210 Hankins, T.H., Rickett, B.J., 1975, in Methods in Comp. Physics 14, 55 Hankins, T.H., Kern, J.S., Weatherall, J.C., Eilek, J.A., 2003, Nature 422, 141 Govoni, F., Taylor, G.B., Dallacassa, D., et al., 2001, A&A 379, 807 Haverkorn, M., Katgert, P., de Bruyn, A.G., 2003, A&A 403, 1031 Heavens, A., Panter, B., Jimenez, R., Dunlop, J., 2004, Nature 428, 6983 Johnston, S., Romani, R.W., 2003, ApJ 590, L95 Kauffmann, G., White, S.D.M., Guideroni, B., 1993, MNRAS 264, 201 Kenney, J.D.P., van Gorkom, J.H., Vollmer, B. 2004, AJ 127, 3375 Keres, D., Katz, N., Weinberg, D.H., Davé, R., 2005, MNRAS in press, astro-ph/0407095 Klypin, A, Kravtsov, A.V., Valenzuela, O., Prada, F., 1999, ApJ 522, 82 Kramer, M., et al. 2005, in prep. Kramer, M., Backer, D.C., Cordes, et al. 2004, NewAR 48, 993 McLaughlin, M.A., et al. 2005, in prep. Morganti, R., Oosterloo, T.A., Tadhunter, C.N. et al., 2005, A&A 439, 521 Moore, B., Katz, N., Lake, G. et al. 1996, Nature 379, 613 Moore, B., Ghigna, S., Governato, F., et al. 1999, ApJ 524, L19 Murphy, E.J., Braun, R., Helou, G., et al. 2005, ApJ submitted Oren, A.L., Wolfe, A.M., 1995, ApJ 445, 624 Quirrenbach, A., Kraus, A., Witzel, A., et al., 2000, A&AS 141, 226 Rees, M.J., Ostriker, J.P., 1977, MNRAS 179, 541 Romani, R.W., Johnston, S., 2001, ApJ 557, L93 Sadler, E.M., Jackson, C.A., Cannon, R.D., et al., 2002, MNRAS 329, 227 Schulz, S., Struck, C. 2001, MNRAS 328, 185 Spergel, D.N., Verde, L., Peiris, H.V., et al., 2003, ApJS 148, 175 Stappers, B.W., Braun, R., Edwards, R., et al. 2005, in prep. Storrie-Lombardi, L.J., 2000, ApJ 543, 552 Treu, T., Ellis, R.s., Kneib, J.-P., et al. 2003, ApJ 591, 53 van der Hulst, J.M., Sadler, E.M., Jackson, C.A., et al. 2004, NewAR 48, 1221 Verheijen, M.A.W., Sancisi, R., 2001, A&A 370, 765 Verheijen, M.A.W., 2004, in IAUC 195, A. Diaferio (ed.), p.394 Weiler, K.W., Van Dyk, S.D., Sramek, R.A., Panagia, N., 2004, NewAR 48, 1377 Zwaan, M.A., Staveley-Smith, L., Koribalski, B.S., et al. 2003, AJ 125, 2842

5 Motivation of Investment Plan The availability of the first large synthesis arrays; the WSRT in 1970 and the VLA in 1980, revolutionized radio astronomy by enabling radio frequency imaging with a combination of high sensitivity, high spatial and spectral resolution and high dynamic range. These arrays constituted a leap in performance and the associated astrophysical discovery space over the previous generation of filled aperture radio telescopes by between one and two orders of magnitude.

We are now on the threshold of a similar revolution in performance and discovery space enhancement, again by between one and two orders of magnitude. But in this case, rather than being enabled by mechanical improvements to the receiving system, the leap is enabled by advances in antenna design and digital electronics. Ultimately, the SKA will take advantage of all these developments, while in the intermediate time frame an order of magnitude increase in capability can be realized with only a modest incremental cost over that of the current generation systems.

The means for achieving this remarkable performance gain is the placement of a fully-sampled, low-noise, wide-bandwidth receiver array in the focus of each parabolic dish of a synthesis array instead of the single receiver element that current systems employ. This is comparable to the great performance leap of optical telescope systems in the past decades when they made the transition from a single

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photometer in the telescope focus to large-format CCD detector arrays. The technology that enables this paradigm-shift in radio telescope design has been developed in the course of Research and Development for the Square Kilometre Array (SKA) and Low Frequency Array (LOFAR) projects, particularly within the ASTRON institute (as described in more detail in Section 8 below).

The great scientific promise of this technology has been recognized simultaneously by three groups around the world, centered in the Netherlands, Australia and South Africa. Australia and South Africa are both being considered as possible sites for deployment of the SKA. Both of these groups are committed to deployment of an SKA pathfinder telescope array on their proposed site regardless of whether the final SKA site choice is in their favor. They are pursuing this course of action in the interest of enabling scientific discovery within their own user communities and developing greater technical expertise that will be to their benefit regardless of where the SKA is finally sited. Both groups have been successful in obtaining partial funding of their pathfinder instruments from the respective national and/or local governments and are now pursuing full funding of these concepts.

Within the Netherlands, we are in a very advantageous position to enable major scientific discoveries in this field. Not only have we been actively pursuing the relevant technological R&D in the past decade, which gives us a development head-start of several years over groups elsewhere in the world, but we also have at our disposal an existing hardware infra-structure for the deployment of focal plane array systems, which allows their application to achieve a major scientific return on both a shorter timescale and at a fraction of the project cost.

We are cooperating closely with both the Australian and South African project teams on two critical aspects:

• A coordinated system design for as many components as possible; including antenna, beam-forming and correlator systems.

• A reciprocal preferred scientific access agreement to all three facilities.

We choose to develop receiving systems jointly with our international partner institutes and then deploy them in our existing infra-structure for the following reasons:

• to ensure that the research needs of our community are met with these new, ground-breaking systems with a maximum scientific return for our financial investment;

• to minimize the costs of realizing the desired scientific capabilities, both for us and for the international partners;

• to reinforce our leading position in the organization of the research field by providing key technologies that will determine the research agenda in the future;

• to benefit certain studies greatly by having overlap with the Sloan wide-area optical survey (SDSS) of the Northern Hemisphere and allowing complementary observations with the LOFAR facility;

• to benefit certain studies greatly by gaining preferred access to the two new radio facilities located in the Southern Hemisphere, thereby allowing complementary observations using ESO telescopes in Chile for optical-IR and mm-wave frequencies.

Our system acronym “APERture Tile In Focus” (APERTIF) seems appropriate since it will provide a first taste of the scientific opportunities that will accompany full-scale deployment of this technology within the SKA starting toward the middle or end of next decade. With this proposal we enable a very significant beginning to be made on many of the key SKA science drivers in the period 2008 to ~2015, as we described in more detail in Section 4.

The Key Science teams which are represented by our proposal co-investigators will carry out ground-breaking research in the fields of:

• Galaxy Evolution, Cosmology and Dark Energy • The Origin and Evolution of Cosmic Magnetism • Pulsars as tools for fundamental physics and astrophysics • The Dynamic Radio Sky

This research will represent a major contribution to the scientific themes of our community as presented in its strategic plan (Astronomy in the Netherlands, Strategy 2001 – 2010) and in the research networks of our top research school NOVA (http://www.strw.leidenuniv.nl/nova/research.html).

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APERTIF yields a fully complementary scientific capability to that provided by LOFAR, which will be operational in the same time-frame, by extending the LOFAR wide-field digital telescope concept to a ten times higher frequency range. The higher frequency band of APERTIF allows the neutral hydrogen and hydroxyl spectral lines to be employed as kinematic probes as well as enabling the study of star formation, cosmic magnetism, pulsars and transient phenomena into regions of 100 times greater thermal depth (in view of the λ2 dependence of many propagation effects). Together, the LOFAR and APERTIF systems will enable essentially all of the key SKA science drivers to be scouted by our astronomical community. Discoveries made with one of these next-generation telescopes can be supplemented with immediate follow-up on the other system. In this way our astronomical community will be uniquely positioned to play a leading role in the SKA era.

In the following sub-section we will briefly outline the proposed system design.

5.1 Basic Instrument Designs and Capabilities The Australian and South African telescope projects each involve construction of 20 parabolic dish antennas of 15 m diameter that will be outfitted with Focal Plane Arrays. Within the Netherlands we have the significant cost advantage of using an existing telescope infra-structure, the 14 parabolic dishes of 25 m diameter on the Westerbork site. In overall specs the three systems are quite similar, and the three groups are cooperating extensively to share technologies and minimize costs. The Australian array is called the eXtended New Technology Demonstrator or xNTD, and the South African array the Karoo Array telescope or KAT.

The specific receiver array foreseen covers the frequency band of 850 to 1750 MHz with an array of 8 by 8 active dual polarization antenna elements. Each of the signal paths is digitized and combined to form a total of 25 digital beams of 300 MHz bandwidth for each polarization. Receiver arrays of this type are provided for each telescope in the synthesis array. The 25 beams from each telescope are then centrally correlated. The specifications for system noise temperature and digital beam aperture efficiency are: Tsys < 50 K and ηa > 75 %. The correlator will provide all four polarization products at a spectral resolution of 20 kHz (corresponding to 4 km/s in the neutral hydrogen spectral line) over the 300 MHz bandwidth (or higher spectral resolution for reduced bandwidth) for all 25 digital beams. By placing fourteen receiver arrays in the prime focus of the existing mechanical infrastructure at the Westerbork site it will be possible to achieve an instantaneous field-of-view (FOV) of about 8 degree2 at a physical sensitivity of Aeff/Tsys > 100 m2/K. These specifications can best be appreciated by comparison with existing and planned observing systems. Compared to the WSRT array, the APERTIF system corresponds to a 50-times greater (25 beams, twice the bandwidth) imaging speed for radio continuum applications or alternately as a 7-times higher (square root of 50) sensitivity obtained for a given FOV in a given observing time. A competitor is the US Very Large Array, which is currently scheduled to be upgraded in 2009 (yielding the “EVLA” with an incremental cost of 80 M$) and will have a FOV in the 1 – 2 GHz band of about 0.32 degree2 and a physical sensitivity of Aeff/Tsys = 220 m2/K. The APERTIF system will provide a higher imaging speed than the VLA for both wide-field spectral line and (bandwidth-limited) continuum applications of a factor of 5 (25 beams times (100/220)2) or alternately more than a factor of 2 higher sensitivity obtained for a given FOV in a given observing time. Our partner institutes plan to place twenty receiver arrays in the prime focus of the 15 m paraboloids of each of the Australian xNTD and the South African KAT. Each of these projects has an estimated budget of about 50 M€. These systems will achieve an instantaneous field-of-view (FOV) of about 22 degree2 at a physical sensitivity of Aeff/Tsys > 50 m2/K. As such, the APERTIF system deployed on the WSRT infra-structure will have a 1.5 times higher (8/22 times (100/50)2) survey speed. It is clear that the APERTIF system will define state-of-the-art performance in the 1 – 2 GHz frequency band in the pre-SKA era, significantly out-performing all current and planned systems at a very modest incremental cost. We will also acquire preferred access to a comparable capability in the Southern Hemisphere on the xNTD and KAT systems.

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6 National Importance and Scientific Accessibility We have sketched the science that the requested investment will make possible. This science addresses in unique ways the science goals of our community, as expressed in its strategic planning and in the structure of its top research school, NOVA.

In addition, the project will be important to our community for non-scientific reasons. It will guarantee access to unique forefront radio facilities in both the Northern and Southern Hemispheres and will strengthen ASTRON’s reputation as a competent enabling institution on the global stage.

Scientific accessibility to the APERTIF facility, as with the existing Westerbork telescope, will be awarded on the basis of scientific excellence, as determined by a peer review of proposals for observing time. Since many of the science goals outlined in Section 4 are best-served by a coordinated wide-field survey, a large fraction of the observing time in the first 5 years of operation will be reserved for such a program, contingent on successful peer review. The Key Science Team members, listed at the outset of this request, are expected to play a major role in planning for and carrying out this coordinated survey program. In addition, we have agreed with our international partners a reciprocal preferred access status of our respective user communities to all three instruments: APERTIF, xNTD and KAT.

Figure 7.1: The frequency coverage and instantaneous field-of-view of current and planned facilities are overlaid on the spectral energy distribution of a nearby star-burst galaxy. The APERTIF frequency band includes the neutral hydrogen and hydroxyl spectral lines between red-shifts of about 0 and unity as well as the continuum spectrum near 1 GHz, which is well-suited to the study of distant star-forming galaxies and the Galactic and Local Group pulsar populations. In those cases where frequency coverage overlaps, only the single most sensitive wide-field facility is shown. The instantaneous FOV of the different facilities is indicated by the vertical extent of the colored lines, which vary by more than seven orders of magnitude. The eight square degree FOV of APERTIF redefines the state-of-the-art for sensitive wide-field imaging programs.

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7 International Positioning Our community plays an important role in the international development of astronomy. We intend to consolidate and extend this position in the coming decade. Our strategy to realize this continues to be a combination of excellence in research with the development of new forefront facilities.

As the scale of facilities increases and the collaborations to achieve them become more extensive, (non-scientific) politics begin to play an ever more important role in the decision making. As a small country, we are vulnerable and must not only continue to do excellent research but also to make ourselves desirable partners in future collaborations for facilities development. The current situation is an excellent example of the success of our strategy to date: both the Australian and South African projects desire our participation and are eager to carry out joint development and exchange telescope access to achieve that participation. By making optimum use of our existing infra-structure and intellectual property investments we are able to reach agreements with these partners on an equal footing, despite the fact that our financial contribution is much smaller than theirs.

With regard to the wide-field performance of the APERTIF system, we have already noted in Section 5 that it is unsurpassed at GHz radio frequencies by any existing or planned facility. The two “sister” facilities of our collaboration in the Southern Hemisphere, xNTD and KAT, are each within a factor of two of the APERTIF in terms of their survey speed, so that together they will provide a similar capability in the south to that provided by APERTIF in the north. The next contender in this frequency range is the (upgraded) EVLA, which trails in survey speed by a factor of 5. Particularly given the many other interesting applications which can be pursued competitively by the EVLA (in higher frequency bands and at higher spatial resolutions), it is clear that the APERTIF will be the premier Northern Hemisphere wide-field survey facility.

In Figure 7.1 we provide an overview of the frequency coverage and relative field-of-view (FOV) of an overview of current or planned astrophysical observatories between radio and ultra-violet frequencies. While there is some degree of overlap in frequency coverage in a few cases, we display only the single most sensitive wide-field telescope in each band. The instantaneous FOV is indicated in units of square arcseconds on a logarithmic scale, since there is a variation in this parameter by about seven orders of magnitude. To facilitate comparison we also tabulate the FOV at the low and high frequency ends of each plotted band in the Table below. As can be seen from this comparison, the APERTIF system sets a new standard for high sensitivity wide-field surveying at GHz radio frequencies.

Telescope λmax–λmin

(units)

LOFAR 10 – 0.8

m

WSRT 80 – 50

cm

APERTIF 40 – 17

cm

EVLA 15 – 0.7

cm

ALMA 3 – 0.5

mm

Spitzer 300 – 5

µm

VLT 5 – 0.4

µm

λmax FOV (arcsec2)

1.3x109 1.3x108 1.0x108 1.2x106 3000 3.6x105 3.6x105

λmin FOV (arcsec2)

2.1x107 1.9x107 1.0x108 7.8x104 80 3.6x105 3.6x105

Table 7.1: The wavelength coverage and instantaneous field-of-view of current and planned facilities. In those cases where wavelength coverage overlaps, only the single most sensitive wide-field facility is tabulated.

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8 Strategy of the institution with regard to the investment This proposal is an important step in a long term, major line of strategic investment at ASTRON that began in the mid-1990’s. At that time it was decided that a major paradigm shift in the technology of radio telescopes would be required to make the next generation of instruments, including the Square Kilometre Array, possible. While the cost of the mechanical antenna structure dominates conventional designs, it was concluded that it should be possible to develop telescopes employing large numbers of very simple antennas whose cost is dominated by the electronics and software, such that it will decrease with time. The physics of these array antennas is similar to the phased array radars familiar in military applications, but the practical implementation is very different as regards noise performance, bandwidth and cost. A grant from NWO/GB-EW allowed ASTRON to carry out an initial study of array antennas and the signal processing chain that is required to implement the new ‘software telescopes’. This initial study resulted in two lines of further development. One line focused on the signal processing chain, the technologies of which are closely linked to developments in the commercial ICT sector. This work has culminated in the LOFAR project, developed on regional funding (SNN, Province of Drenthe) and NWO, and currently being constructed on a BSIK subsidy. LOFAR can be seen both as a pathfinder for the SKA and a major innovative instrument in its own right. Much of the signal processing architectures and software developed for LOFAR can be directly reused for APERTIF. The LOFAR Central Processor can in principle be used as a (fall-back) correlator for APERTIF. The second line of development concerns the front-end receiver/detector, an effort that aims at simultaneously achieving a high degree of component integration (of the antenna and the first stage of analog processing), a wide bandwidth and a low noise. Here EU grants have enabled further technology development for detection at intermediate frequencies. In FP5, the FARADAY project explored design approaches further, and in FP6 the PHAROS project aims to develop a prototype operational focal plane array. APERTIF is a direct successor to these projects and aims to put the knowledge developed to date into an operational focal plane array system on large synthesis array telescopes. It will enable the first ground-breaking science to be done at these frequencies with these new technologies that have been developed over the past decade. The new array antenna technologies have significant operational advantages over conventional designs, including in particular the possibility of producing multiple, independently steered, measurement beams simultaneously; in essence multiple software telescopes sharing the same aperture. Employed in the aperture plane, they permit monitoring of the whole visible sky as well as simultaneous pointed observations, and are expected to revolutionize the study of transient phenomena in the cosmos. Hence European radio astronomers have selected the concept for development in the context of the SKA; they have recently agreed on a 40M€, 30 institution EU FP6 Design Study (SKADS) project to that end. APERTIF has the more modest goal of producing array antennas for focal plane rather than aperture plane use, but it will also play an essential, complementary and synergetic role to the SKADS project. That is, SKADS remains a study that in and of itself will not result in cutting edge science, while APERTIF aims to build on the on-going studies and actually enable world-class astrophysical research. We expect the synergy will yield benefits to both efforts. We note in passing that having ASTRON leading, and the South African and Australian partners participating in, the SKADS project should make the synergy between SKADS and APERTIF readily achievable in practice. In addition to these hardware development lines, ASTRON has set up a strong program in software and algorithm development for the control and post-processing of large distributed facilities. Software is increasingly becoming a key enabling factor for the success of the next generation of radio telescopes. ASTRON has a leading role in the SKA Calibration and Software Engineering working groups. The Monitoring and Control system developed for LOFAR will be used for APERTIF. The post-processing algorithms, high performance processing pipelines and end-user software that are now being developed for the WSRT and LOFAR form a firm foundation for APERTIF and these will be further extended.

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8.1 Array technology development at ASTRON In the mid-1990’s it was established that to realize a Square Kilometre Array at reasonable cost, new concepts had to be developed to construct the very large apertures at a small fraction of the cost of conventional technology. This observation has initiated a number of research and development activities at several international centres. ASTRON initiated a new line of research and concentrated its SKA R&D technology roadmap on the development of array technology. Array technology is considered an essential component to enable the next generation of telescopes and is being developed for application in two front-end concepts. For the lower frequencies (the SKA low band) array technology is utilised in aperture arrays (or flat panel phased arrays). Instead of using extremely large reflector antennas that would have been required at these frequencies, a large number of small distributed antenna elements are used. The feasibility of aperture array technology was demonstrated in a number of successive demonstrator projects: the Aperture Array Demonstrator (AAD), the One Square Meter Array (OSMA) and the Thousand Element Array (THEA) and in the LOFAR telescope. Based on these successful demonstrations the aperture array concept has now been adopted as the European SKA low band concept. For higher frequencies the array technology is utilised in a different manner. The aperture array concept is not cost-effective at higher frequencies because the cost per square meter of collecting area increases quadratically with frequency. Therefore, an alternative front-end technology is being considered for the SKA high band: focal plane arrays. Focal plane arrays utilise reflectors to concentrate the received signals onto an antenna array to increase their collecting area. Additionally, this technology allows for cryogenic cooling of the centralised receivers to obtain lower noise temperatures. This “smart feed” technology brings the advantages of aperture array technology to reflector antennas: multi-beaming (enlarging the field-of-view), RFI suppression and highly optimised illumination of the reflector. The latter allows a lowered spill-over level resulting in a significant reduction of the system noise level. Array technology development is a key research area of the ASTRON R&D division. Although the aperture array and focal plane array antenna concepts are complementary, there is a very strong overlap in the relevant research development since they both utilise array technology. The investments in, and results of, the above programs are reflected in the international position of ASTRON: ASTRON is considered the technological leader for the application of array technology in both the areas of aperture arrays as well as focal plane arrays in radio astronomy. ASTRON has shared the results of its array technology at many conferences, organised dedicated phased array related sessions and has organized two International Focal Plane Array workshops in which all major countries involved in SKA antenna R&D presented their advances and future plans.

Figure 8.1: Illustration of the SKA aperture array and small dishes with smart feeds hybrid concept. Research and development activities are underway at several other international centres that focus on alternative technologies. For example, novel concepts for very large, single-aperture antennas are being considered. Plans are well developed for construction of different prototype telescopes within the next several years. A process for convergence on a technological concept(s) for the SKA has been agreed on and should lead to a technology choice in 2008. The results of the xNTD and KAT systems are therefore

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essential to demonstrate the feasibility of the small dishes in combination with focal plane arrays concept. The R&D effort for APERTIF is a key enabling part of these pathfinder systems.

8.1.1 Focal Plane Array Research

In the field of focal plane array technology for parabolic reflectors, ASTRON has concentrated on the application of focal plane arrays in deep reflectors (e.g. Ivashina 2002). The FARADAY project, which was completed in 2005, has successfully demonstrated the feasibility of using two-dimensional receiver arrays installed in the focal plane of a reflector telescope (e.g. Ivashina et al. 2004). ASTRON concentrated on the use of dense array antennas (i.e. arrays with sufficiently small element spacings). In contrast to multi-feed horn antennas, dense array feeds produce overlapping beams resulting in a large, contiguous field-of-view (Ivashina et al. 2002). The enabling technology that was developed within FARADAY consists of the design of wide-band phased array antennas, low noise amplifier (LNA) design, beam forming schemes optimised for focal plane arrays and system modelling. Methods for the detailed design of focal plane arrays were developed; for example to determine the required number of elements, their arrangement and the optimal excitation coefficients. A system model was constructed for performance analysis and optimisation (Maaskant 2004, Simons 2005). The FARADAY project has delivered a two-beam 2 – 5 GHz focal plane array demonstrator that was tested in one of the Westerbork reflector telescopes. Very good agreement was observed between the designed and realised aperture illumination patterns and beam patterns (Ivashina et al. 2005).

The PHAROS project, which is funded by the European Commission FP6 RadioNet program, is a three year project that was started in 2004. Its main objective is the development of a 4 – 8 GHz focal plane array demonstrator for deep reflectors with four beams (using an analog beam former) that should

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provide a 50 K system temperature (Bij de Vaate, 2005). Hence the LNA’s will be cooled to 20 K. The PHAROS demonstrator will be tested at several radio telescopes in Europe and Australia. For the objectives of the FARADAY and PHAROS projects the usage of an analog beam former was sufficient. To further extend the field-of-view and the flexibility of the system an increased number of beams is necessary. Because of its complexity this can only be realised with a digital beam former.

8.1.2 Aperture Array Research

The use of phased array technology for the low band SKA makes the construction and operation of a large radio telescope in this frequency range feasible and cost-effective. Electronic beam steering and the ability to make multiple beams simultaneously provides: scanning over a large angle, tracking multiple sources that are widely separated or adaptive suppression of interferers in dedicated beams. Through the stepping stones of AAD (Hampson et al. 1998) where experience with digital beam forming and adaptive nulling was gained, OSMA that further explored the multiple beam capabilities of the phased arrays and wideband antenna technologies (Smolders et al. 2002, Hampson et al. 2002), the THEA platform was developed. THEA is an out-door phased array system with 256 broadband receiving antenna elements (e.g. Kant et al. 2000, Smolders 2000). Beam steering is done by a combination of RF and digital beam forming. THEA is able to make multiple beams over the sky simultaneously. In addition, adaptive beam forming may be applied to suppress EMI sources. THEA demonstrated successfully the ability to detect and track strong astronomical radio sources in the frequency range from 600 -1700 MHz in the presence of interfering signals (e.g. Bij de Vaate 2002, Wijnholds et al. 2005). Recently, a THEA tile has been sold to CSIRO in Australia who will used it as a focal plane array in one of their reflector antennas to conduct digital beam forming experiments. The next step in the aperture array research is the development of a large scale demonstrator called EMBRACE (Kant et al. 2005, Bij de Vaate 2004) within the EU FP6 Program SKADS. Building on the results of the THEA concept, EMBRACE will demonstrate that the aperture array technology can be made cost-effective and that high performance can be maintained. The EU SKADS program further includes overall studies of the SKA science, technologies, architectures and cost-model system to prepare for the SKA technology choice in 2008. Major parts of these studies are directly relevant to APERTIF.

8.1.3 Low cost manufacturing

Both aperture arrays and focal plane arrays require large numbers of receiver elements. Therefore the cost of an antenna element has a significant impact on the cost of the complete system. PACMAN, a research project funded by the Ministry of Economic Affairs, aims at developing integrated technology for the design and manufacturing of mass-market low cost phased array antennas that can be applied in both aperture arrays and focal plane arrays. PACMAN focuses on four areas of technology that can lead to cost reduction:

- connector-less connection technology - 3-Dimensional RF circuit integration - Multi-functional radio frequency substrates - structural & environmental aspects.

Close interaction between mechanical and electro-magnetic disciplines and industry is required to develop such technology. The PACMAN project is therefore carried out with our industrial partner Thales, the Eindhoven University of technology and University of Twente. Industrial partners have a direct commercial interest in the technologies developed in PACMAN.

8.1.4 LOFAR

The LOFAR telescope consists of a large number of small antennas grouped in phased array stations. LOFAR was primarily conceived as a science instrument applying the concepts of the phased array concept to low frequency astronomy. However, LOFAR is also a most important stepping stone towards the SKA, since the system architecture and models, signal processing, software systems and calibration

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algorithms developed for LOFAR are directly applicable to the SKA. LOFAR is currently in its final design phase and will enter initial operations at the end of 2006. Full operations are planned for 2008. The R&D performed for the LOFAR project contributes significantly to the realization of an FPA observing system. Developments in LOFAR that are relevant to the APERTIF system are its receiver architecture (especially the experience gained with the direct frequency conversion scheme), the digital station architecture and electronics, and the associated data processing including functions like digital beam-forming, RFI mitigation techniques and station calibration. The monitoring & control software developed for LOFAR will be used for the APERTIF system with only minor modifications. Within the LOFAR project, new approaches towards high-dynamic range calibration and wide field imaging have been developed. The algorithms, high performance processing pipelines and end-user software developed for LOFAR will form the starting point for the data handling and post processing of APERTIF data.

8.2 Array technology in APERTIF The FARADAY and PHAROS projects have proven feasibility and generated technology demonstrators for low-noise, phased receiver arrays to be installed at the focus of radio telescopes. This technology is now at a pre-design level. The final and essential step to prove the feasibility of focal plane array based systems is to incorporate this technology into operational instruments to demonstrate its performance for scientific purposes. Supported by the technology development in LOFAR, SKADS / EMBRACE and PACMAN, ASTRON is in an excellent position to perform this step. Table 8.1 summarizes the technologies required for the realisation of APERTIF and how they have been developed through different projects at ASTRON.

Others THEA FARADAY PHAROS PACMAN SKADS LOFAR Feasibility APERTIF

Architectural design 2003 2004 2006

FPA's at low frequencies 2006

Wide bandwidth 2005 2006

Dual pol phase center 2005 2006

Dual pol 2003 2005 2006 2006/7

Mitigation of truncation effects 2006 2006/7

LNA Design 2005/6 2006 2006/7

2006 2006 2006/7

Architecture (tradeoff mixers/direct sampling) 2001 2005 2005 2006/7

Detailed design 2006/7

Architectural design 2005 2005/6

Detailed design 2005 2006/7

2001 2006 2005 2006/7

2005 2006 2006/7

2004 2005 2006 2006/7

<2005 2001 2005 2006 2006/7

<2005 2005Colors indicate the maturity/relevance level that the activity has or should provide

ConceptFeasiblePre-DesignDesign

EMC/shielding

Cryo Cooling

System design

Array design

Receiver

Digital

Digital optical link

Clock and control

Mechanical design

Analog optical link

Table 8.1: Technology development and maturity for APERTIF

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9 Technical Concept and Budget

9.1 APERTIF System Concept APERTIF will be a full digital focal plane array: every active element will have its own receiver and analog to digital convertor (ADC). Each focal plane array (or antenna “tile”) will consist of 8x8 active elements and will have dual polarization. This results in a total number of 128 active elements per tile. The focus boxes of APERTIF will contain the 128 antenna elements, the low noise amplifiers, the ADC’s and the digital beam forming electronics. The focus box will be a generic design that can be mounted and tested at several radio-telescopes around the world. The analog signal with a 300 MHz instantaneous bandwidth is directly converted into a 4 bit digital signal that is input to the digital beam-former unit. Mounting this unit in the focus box requires adequate shielding of the EMI caused by the digital electronics. The weight of the focus box will increase as a result of this design. The advantage of this approach is that no (optical or coaxial) links between the focal plane array and a beam-forming unit on the ground are required. This leads to both a significant reduction in cost (reduced number of high bandwidth links) and in the system complexity. A high speed optical digital link will be installed between every telescope and the central correlator.

Focal Plane Array system in each Focus Box

Figure 9.1: System Architecture for APERTIF (the dotted box forms the actual Focal Plan Array system) Number of Active Elements 128 Polarizations 2 Frequency Range 850-1750 MHz Tsys 40-50K Instanteneous Bandwidth 300 MHz Number of Beams 25 Subbands 200 Correlator 14x14 correlations

4 pol. products, 16000 spectral channels for each of the 25 FOV in 4 bits.

Table 9.1: System Requirements of APERTIF

Monitoring & Control

Antenna Elements

Digital Beamformer A/D

central Correlator

64 Dual Polarization Active Elements Adaptive

Beamforming

Data Handling & Post-Processing Software

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9.1.1 Antenna array

The FPA antenna element requires a broad bandwidth and dense packing of the array elements to sufficiently sample the electromagnetic fields in the focal plane of the reflector. ASTRON, in collaboration with international partners, has been extensively involved in the development and analysis of a wideband radiator that operates in very dense arrays (e.g. Schaubert 1999, Craeye 2002). It has been demonstrated that a dense array of Vivaldi antenna elements is capable of intercepting the two polarizations of the incident fields over a frequency bandwidths of at least 2.5:1. The array size of 8 x 8 elements is derived from the half-wavelength element spacing at the highest operating frequency and the required field-of-view. In order to achieve a low noise system temperature cryogenic cooling is applied. The large number of low noise amplifiers for FPA systems brings a constraint in the cryostat design in terms of power consumption and thermal leakage. The LNAs will be optimized for power consumption and the connection losses between LNA and antenna element will be minimized; the antenna element array will be placed outside the cryostat to avoid the requirement for a large window.

9.1.2 Digital Beam-forming

The beams (look-directions on the sky) are formed after digitizing and filtering the signal from the active antenna elements. A direct digital conversion receiver scheme is used with 8 bit commercially available A/D converters (4 efficient bits per sample are used for further processing) sampling up to 1.7GHz in selectable frequency zones. This results in a data rate of 13.6 Gbps per element. The signals are processed (filtered into sub-bands and beam-formed in multiple directions) on a FPGA-based reconfigurable platform. This makes the system very flexible and will give it excellent resistance against Radio Frequency Interference. It will also give the system the ability to track several sources at the same time or to increase the instantaneous field of view. The total data rate to the correlator is a function of the number of beams generated and the instantaneous bandwidth. The data rate adds up to 120 Gbps.

9.1.3 Correlator System

The signals from all telescopes are combined in a correlator system. The correlator system will provide continuous imaging capacity for 128 baselines (16 antenna equivalent), 25 beams, 4 polarizations products for the instantaneous bandwidth. These very high processing requirements will be handled with a similar processing technology as was developed for the LOFAR telescope (van der Schaaf et al, 2005). The correlator envisaged for APERTIF will be a cost effective modular and scalable FPGA based system matched to the APERTIF signal processing requirements. The FPGA approach allows flexible and fast reprogramming/reconfiguration of the correlator. It should be noted that the capacity in input data-rate and processing cycles of the LOFAR Central Processor matches the APERTIF signal processing requirements sufficiently well to make it ideal for initial testing and commissioning of the APERTIF system. High speed data-links between APERTIF and the LOFAR Central Processor are available. The correlator will also provide adequate interfaces to calibration and post-processing resources.

9.1.4 Monitoring & Control Software

APERTIF will be operated through an advanced distributed Monitoring and Control system that is based on the system used for LOFAR. This system is built upon a commercial SCADA system, PVSS, and has a System Health Management function to make the instrument self-diagnosing.

9.1.5 Data Handling and Post-processing Software

The huge data-rates produced by the correlator require a substantial amount of automated data handling and calibration. The software required for these tasks will build on the processing pipeline studies for the WSRT carried out in the context of the EU RadioNet program and the NL-Grid project, and the high performance computing software developed for the LOFAR project. The calibration challenges for aperture synthesis at the APERTIF frequencies are well-known. The added complexity of using phased array systems instead of single-feed antennas have been studied for astronomical observations with the LOFAR test station (Boonstra et al, 2005).

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9.1.6 Infrastructure

The placement of new feed-boxes in each antenna will require new infrastructure for the transport of the digital signals to the correlator. The data transport from the focal plane arrays to the correlator will be realised by optical links that allow a data-rate of 10 Gbps. The total rate for each focal plane array system will be 120 Gbps thus requiring 12 optical links. All elements of this link are already available so no further development is required here.

9.2 Project Management The design effort of the APERTIF project is embedded in an international project organization, where the contribution of each institute is based on its specific strength and knowledge and all international developments in the area of Focal Plane Arrays are linked. The project works on the basis of a reference architectural design that can be used as input for each national project. The ultimate goal is to design the best radio-telescope based on focal plane array technology that is possible on a global scale and to minimize overlaps. This approach not only stimulates knowledge transfer among the institutes involved, it also ensures that the funding agencies get the most value for their money. Finally, the astronomers involved in the three projects are able to address cutting-edge astrophysical questions, enabled by the combination of state-of-the-art focal plane technology, digital beam-forming and an advanced correlator. The technical strength of ASTRON on a global scale, as illustrated in both the FARADAY and the PHAROS project (see section 8.1) lies in the analogue part of the FPA system. This leads naturally to a focus for the design effort of APERTIF on antenna systems to be incorporated in the project. Figure 9.2: International collaboration model

KAT (S

APERT

IFPA P t

The project is executed using standard project managthree phases. Each phase is concluded with a review, continuation of the project. An ASTRON R&D phase will precede the actual APERundertaken to investigate critical design issues and remethe PHAROS project. The discussion in section 8 showsmaturation of technologies applied earlier in FARADAYthe detailed system architecture, but these studies will tathe pre-APERTIF R&D phase will be mid-2006 and thseries of Focal Plane Array antenna elements. The Final Design Phase of APERTIF aims at producing is funded by NWO-Groot and the other two are funknowledge gained in FARADAY, PHAROS and from

rojec

xNTD ( )

)

T

ad

IF(NL

A)

ement practices ansuccessful completi

IF project, wherebdy knowledge gaps that most of these and PHAROS. Anoke place on an intere outcome will be d

small series of threed by the partner the international

Aus

d is accordingly divided into on of the review will result in

y a number of studies will be which are not yet covered by studies have as their aim the ther topic to be addressed is national level. Completion of irectly applicable in the first

e FPA systems of which one institutes. Based upon the partners, a first design is

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constructed and tested on three different sites: the WSRT for the Netherlands, KAT for South Africa and xNTD for CSIRO in Australia. During this phase, engineers and scientists from all three projects are expected to contribute to the design and are expected to participate in the antenna element design team at ASTRON. The test results will be evaluated and used for the series production of the actual antenna systems. The APERTIF budget also allocates 2 myr for participation in international working groups that deal with other elements of the FPA system such as A/D conversion, beam-forming, correlator and monitoring & control software. The Production and Integration Phase is the phase where the FPA system and correlator are produced. The system is integrated and tested and accepted after astronomical commissioning.

ID Task Nam e Duration

1 PHAROS 600 days3 ASTRON R&D 280 days4 System Architecture 180 days9 Antenna Array Design 100 days15 Mechanical Design 65 days18 Preliminary Design Review 0 days19 Final Design Phase 446,86 days20 FPA System Design 440 days21 Antenna Elem ent Design 260 days22 Series -1 Production 60 days23 Final Design Review 0 days24 Series -1 Tes t 60 days25 Evaluation of Series -1 60 days26 Phase-1 Correlator 280 days27 Correlator Architectural Des ign 120 days28 Correlator Software Developme 160 days29 Production and Integration Phase 464 days30 FPA System Production 210 days31 Re-des ign 60 days32 Series 1-20 Production 90 days33 Series Tes t 60 days34 Phase-2 Correlator 150,86 days35 Correlator Production 60 days36 Correlator Integration 60 days37 System Test 160 days38 Sys tem Test+Integration 70 days39 Sys tem Commis ioning 90 days

8-6

9-6

5-7

30-8 6-12 14-3 20-6 26-9 2-1 10-4 17-7 23-10 29-1 7-5 13-8 19-11 25-2 2-6 8-9 15-12 23-3 29-6 5-10 11-1 19-4Novem ber April Septem ber February July Decem ber May October March Augus t January June Novem ber April

2005 2006 2007 2008 2009 2010

Figure 9.3: APERTIF Project Planning, including the preceding projects PHAROS and R&D phase. The local project organization is headed by the Principal Investigators who are in charge of the science case, assisted by the International Science Team. The technical development project will be under the control of a project manager who is leading the project team at ASTRON. The systems engineering team in turn is heading a number of work-packages and is communicating with the international systems engineering team in order to stay in line with the international reference design.

PI

Project Management

Systems Engineering Team

International Science Team

International Systems

Engineering

Digital Beamforming CorrelatorAnalog Front End Testbed

IntegrationSoftware

Development

Figure 9.4: APERTIF Project Organisation

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9.3 Budget description The budget estimation is made for a complete system where 14 telescopes are equipped with focal plane array systems, a correlator for processing the data and the software required for monitoring and control of the system. In this proposal, funding is requested for the 14 focal plane array systems. The correlator will be developed with the international partners, JIVE and other institutes to yield the required system in the required time frame. Initial testing and commissioning of the APERTIF system is foreseen with the existing LOFAR IBM BlueGene/L processor, which can also serve as a fall-back option if need be. The cost for the complete development of a focal plane array system from concept to operation amounts to almost € 17 million. This includes the 2.2 M€ from the EU FP6 Pharos project and internal research at 0.7 M€, while the final design and production requires 14.2 M€ as presented in table 9.2. R&D phase, this phase includes the research performed in the FP6 PHAROS project and EU SKADS project and is dealing with the architectural and technological issues that are specific for the APERTIF system. A dedicated work package dealing with the technological issues not covered by the other projects and required to start APERTIF design will start as early as September 2005, it requires 80 K€ hardware and 5 myr. For this phase no NWO-Groot is requested but it is added as matching to the project. In mid-2006, a Preliminary Design Review will ensure that the project is ready to proceed to the next phase. Final design phase of the project, where the focal plane array system is designed, developed and tested and a first small series is produced to obtain experience with a FPA-based radio telescope system. The majority of the development for the focal plane array feed is performed in this phase. A prototype of the front-end is produced and tested as well as a small module of the correlator. After testing and evaluating the design phase-1 is finished. The manpower budget for this phase is 22 myr and the hardware cost are 0.3 M€. In mid-2007 an international Final Design Review will provide a Go-No-Go decision moment. Table 9.2 specifies the manpower associated with the design and production of the FPA system. The manpower requested for this project consists of scientists and engineers that are specialized in the design of radio astronomy systems.

Manpower(myr)

FPA system DesignProject Management 2System Engineering 2Analog SectionAntennna Element 1LNA Design 1Receiver Design 4Analog Photonic Link 2Mechanical DesignHousing 4Cryostat 1Digital SectionDigital Filter/Beamformer 4Backplane 0,5Clock Distribution 0,5

Total Manpower 22 .

Table 9.2: Specification of the manpower required for the design and production of the FPA systems.

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Production & Integration phase: This phase involves the production of the complete series of the FPA systems containing the antenna unit and digital beam-former as well as the implementation of the correlator. The system is integrated at the WSRT and commissioned on a technical level. The manpower budget for this phase is 4 myr and the associated hardware costs are 5.2 M€. The amount requested from NWO-Groot is 7 M€, which is required for the design and production of 14 FPA systems. The total project budget from concept until commissioning is specified in the table below:

System Nr. Cost (€) xNTD/KAT Correlator Project LOFAR ASTRON NWO-Grant

FPA System 14 € 7.583.273 € 644.000 € 6.939.273Correlator 1 € 4.374.768 € 4.374.768Infrastructure € 975.000 € 975.000MAC Software € 1.250.000 € 1.250.000

€ 14.183.041

Funding

Table 9.3: Cost for design and production of the APERTIF system. The xNTD/KAT and LOFAR contributions are in kind.

10 Exploitation We expect the scientific exploitation of our FPA systems to take place over a 5 to 10 year period. The specific research projects making use of the facility will be granted access through peer review of proposals. They are expected to fit well into the long term themes of the community and therefore are expected to receive support from both the national research school NOVA and the open competition of the GB-EW at NWO. Regarding operational support at ASTRON, the funding situation is at present under review. Two developments are relevant. First, plans are being developed to merge the operational activities of LOFAR, which begin in earnest early in 2007, and those of the WSRT. We expect operational merging to yield both improved LOFAR operations and cost savings for the WSRT. Second, in June of this year, the ASTRON institute was reviewed by an international panel of experts that was recruited and supervised by NWO. We have received an ‘Excellent’ final review of our program. Discussions will take place in the coming months with the General Board of NWO concerning the annual subsidy that ASTRON will receive in the coming 6 years. A modest increase will ensure that operational exploitation of the WSRT can proceed as desired. A decrease in the subsidy could present a major problem, independent of the developments outlined in this proposal. We expect to be told our future in this regard in the coming months. In general, we foresee increasing user pressure for long term survey programs of several years duration. With APERTIF this pressure is likely to increase even more. This will imply operational simplification over the current situation, in which many small observing allocations yield a large operational overhead for both hardware modifications (such as telescope reconfiguration) and system set-up and scheduling requirements. Our participation in the three-way partnership: APERTIF, xNTD and KAT, will in any event provide reciprocal preferred access to the two new Southern facilities, which will enable our scientific program to be addressed. We have built Go-NoGo decision points into the project planning that will allow us to restructure the effort as necessary to accommodate any evolution in circumstances.

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11 Technical References

Focal plane arrays, FARADAY and PHAROS

- Simons J., M. Ivashina, J. G. bij de Vaate, “System Model of Focal Plane Arrays in Deep Dish Radio Telescopes”, EuMC 2005, Paris, France, Oct. 2005.

- Bij de Vaate J.G., M. Ivashina, “Focal Plane Arrays: Radio Astronomy enters the CCD Area”, URSI GA 2005, Delhi, India, Oct. 2005

- Ivashina M.V., R. Maaskant, J.G.Bij de Vaate, H. van der Marel, "Holographic performance verification of a Focal Plane Array proto type designed with conjugate field matching method.” the 28th ESA Antenna Workshop on Space Antenna Systems and Technologies, Noordwijk, the Netherlands, May 2005

- Ivashina M.V., J. Simons and J.G. bij de Vaate, “Efficiency Analysis of Focal Plane Arrays in Deep Dishes”, Experimental Astronomy, 2005

- Maaskant R., E.E.M. Woestenburg and M.J. Arts, “A generalized Method of Modeling the Sensitivity of Array Antennas at Sytem Level”, EuMC 2004, Amsterdam, The Netherlands, Oct. 2004.

- Ivashina M.V., J. G. bij de Vaate R. Braun, J.D. Bregman, “Focal Plane Arrays for large Reflector Antennas: First Results of a Demonstrator Project”, Proc. SPIE, Vol. 5489, pp 1127-1138, SPIE conference, June 2004.

- Ivashina M.V., J. D. Bregman, J.G. bij de Vaate, Li Li, A.J. Parfitt, W. van Cappellen “Experimental Results for a Focal Plane Array, Synthesized with Conjugate Field Method”, Conf. proc IEEE AP-S/URSI, Monterey, June 2004.

- Ivashina, M.V., Klooster, K.G. van ’t, “Focal Field Analyses for Front-Fed and Offset Reflector - Antenna”, Proceedings 2003 APS, Vol 2, pp.750-753, Columbus, Ohio, June 2003. - Ivashina M.V., et.al. “A Way to Improve the Field of View of the Radiotelescope with a Dense

Focal Plane Array”, CriMiCo conference, Sebastopol, Ukraine, Aug. 2002. - Ivashina M.V., et.al. “Experimental Synthesis of a Feed Pattern with a Dense Focal Plane Array”,

European Microwave Conference, Milaan, Italy, Sept. 2002. - Ivashina M.V., et.al., “Focal Fields in Reflector Antennas and Associated Array Feed Synthesis

for High Efficiency Multi-Beam Performances”, ESTEC Antenna workshop, Noordwijk, the Netherlands, Sept. 2002. SKA, AAD

- Hampson G.A., M.J. Goris, A. Joseph, F.M.A. Smits, “The Adaptive Array Demonstrator”, Proc. 8th IEEE Digital Signal Processing Workshop, Bryce Canyon, USA, August 1998 SKA, OSMA

- Hampson G.A., A.B. Smolders, G.W. Kant, “Hierarchical beamforming aspects of OSMA”, Signal Processing and its Applications, Aug. 2002

- Smolders A.B., G. Hampson, “Deterministic RF nulling in phased arrays for the next generation radio telescopes, Antennas and Propagation Magazine, IEEE, Aug. 2002 SKA, THEA

- Wijnholds, S.J., A.G. de Bruyn, J.D. Bregman, J.G. Bij de Vaate, “Hemispheric Imaging of Galactic Neutral Hydrogen with a Phased Array Antenna System”, Experimental Astronomy, 2005

- Bij de Vaate J.G., G W Kant, "The Phased Array Approach to SKA, Results of a Demonstrator Project", European Microwave Conference, Milaan, Sept. 2002

- Tol S. van de, A J Boonstra, J G Bij de Vaate, A van Ardenne "Multiple satellite detection with a prototype new generation phased array radio telescope", ESA Antenna workshop, Noordwijk, Sept. 2002

- A.B. Smolders, G.W. Kant, “THousand Element Array (THEA)”, 2000 IEEE AP-S International

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Symp., Salt Lake City, USA, Vol. 1., pp 162-165, July 2000. - Kant G.W., A.W. Gunst, A.B.J. Kokkeler, A.B. Smolders, "Receiver Architectures of the Thousand

Element Array (THEA)", SPIE conference, Munchen, March 2000 SKA, SKADS/EMBRACE

- Bij de Vaate J.G., P.D. Patel, A. van Ardenne, “Ramping up to the Square Kilometre Array: A 1000m2 Aperture Array Prototype”, European Microwave Conference, Amsterdam, The Netherlands, Oct. 2004

- Kant G.W., Patel P.D., van Houwelingen, J.A., van Ardenne A., “Electronic Multi-Beam Radio Astronomy Concept: EMBRACE The European demonstrator for the SKA program”, URSI GA 2005, Delhi, India, Oct. 2005.

Antenna Arrays

- Schaubert D.H. et al., “Wideband Vivaldi arrays for large aperture antennas”, Proc. Persp. On Radio Astronomy:Technologies for Large Antenna Arrays, Dwingeloo, April 1999.

- Craeye, C.V.G. et al., “Analysis of infinite and finite arrays of tapered-slot antennas for SKA”, European Microwave Conference Milan, September, 2002.

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12 Abbreviation list AAD Aperture Array Demonstrator ADC Analog to Digital Convertor AGN Active Galactic Nucleus ALMA Atacama Large Millimetre Array APERTIF APERture Tile in Focus BSIK Besluit Subsidies Investeringen Kennisinfrastructuur CCD Charge Coupled Device CMB Cosmic Microwave Background CSIRO Commonwealth Scientific and Industrial Research Organisation (Australia) EMBRACE Electronic Multi-Beam Radio Astronomy Concept EMC Electro Magnetic Compatibility EMI Electro Magnetic Interference ESO European Southern Observatory EU European Union FARADAY Focal-plane Arrays for Radio Astronomy, Design Access and Yield FIR Far Infra-Red FOV field-of-view FP Framework Program FPA Focal Plane Array FPGA Field Programmable Gate Array GRB Gamma-ray Bursts Gyr 109 years HI Neutral hydrogen HST Hubble Space Telescope ICT Information-Communication Technology IDVs Inter-day variables IFPA International Focal Plane Array Project IGM Inter-Galactic Medium IR-UV Infra-Red Ultra-Violet ISM Inter-Stellar Medium ISS Interstellar Scattering IR Infra-Red KAT Karoo Array Telescope (South Africa) LNA Low Noise Amplifier LOFAR Low Frequency Array M31 / M33 Messier 31 (the Andromeda Galaxy) and Messier 33 (the Triangulum Galaxy) Mpc Mega-parsec MSPs Milli-Second Pulsars myr Manyear

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NHI Neutral hydrogen column density NOVA Nederlandse Onderzoeksschool voor Astronomie NWO. Nederlandse Organisatie voor Wetenschappelijk Onderzoek NWO-GB-EW NWO GebiedsBestuur Exacte Wetenschappen NIR Near InfraRed OSMA One Square Meter Array P(k) Power at spatial frequency, k PACMAN Phased Array Communication Antenna for Mass market Application Needs PHAROS Phased Arrays for Reflector Observing Systems PI Principal Investigator PMAS IFU Integral Field Unit PSR Pulsar PVSS Prozessvisualisierungs- und Steuerungs-System QSO Quasi-stellar object R&D Research & Development RF Radio Frequency RFI Radio Frequency Interference RM Rotation Measure SCADA Supervisory Control and Data Acquisition SDSS Sloan Digital Sky Survey SKA Square Kilometre Array SKADS SKA Design Studies SN Supernovae SNN Samenwerkingsverband Noord Nederland Spitzer Sptizer Space Telescope THEA Thousand Element Array Tsys System Temperature VLA Very Large Array VLA NVSS Very Large Array National Radio Astronomy Observatory VLA Sky Survey VLT Very Large Telescope WHIM Warm Hot Intergalatic Medium WSRT Westerbork Synthesis Radio Telescope xNTD eXtended New Technology Demonstrator (Australia) ΛCDM Lamba-Cold-Dark-Matter

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13 APPENDIX A: Letters of support

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