Astronomy, Radio Sources and Society
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Transcript of Astronomy, Radio Sources and Society
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Astronomy, Radio Sources and Society
Extragalactic radio sources and their importance for astronomy
Leiden 10-13 June 2013
Ron EkersCSIRO, Australia
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George Miley
The largest, the furthest, the most powerful, and to some of us the most fascinating objects known in
the Universe are to be found among the radio sources associated with some elliptical galaxies
and QSO’s. In recent years it has become apparent that they are also objects of considerable
beauty.
Ann. Rev. Astron. Astrophys, 1980
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AAS Long Beach 3January 7, 2013 Mt Palomar 200”
50th Anniversary of the Discovery of Quasars
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Geese
Hoyle, Burbidge and Narlikar
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Linear size distribution of radio galaxies
3CR radiogalaxiesa Linear plot with
linear bins↕
b Log plot with log bins
Ekers & Miley 1977
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Halley Lecture23May2007
The Scientific Method Developed during the 17th century
– Develop an hypothesis – Make predictions– Verify with observations (or discard hypothesis)
Eg Newton's theory of gravity – at the time Newton died it was still merely a hypothesis– It explained everything from planets to falling apples– It was verified by the return of Halley’s comet in 1758– Since than it made many predictions
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Astronomy
Most astronomy papers today are explanations of observed phenomena.
Predictions usually fail and it is considered normal practice to adapt the theory to fit the observations.
These theories may not be wrong, but without predictions we have no reason to accept them
Many examples in our interpretation of radio galaxies The role of the sceptic in science
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Where we are going from here
Some of the enabling technology Martin Rees and the Wireless Internet Radio Galaxies from the beginning QSO 50th anniversary Blackholes Some Extragalactic Radio Source Highlights Galaxy formation and the early Universe
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Cambridge One-Mile Telescope: 1962
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First Cambridge Earth Rotation Synthesis Image
June 1961 North pole survey 4C aerials 178 MHz Computations and graphical
display used EDSACII 7 years after Christiansen
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Benelux Cross1963
Joint Netherlands – Belgium OEEC (now OECD) agreement Christiansen et al design 100x 30m + 1x 70m dish 21cm 1.5km
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Science Goals for Benelux Cross Oort - OECD Symposium
(1961)– Primary goal
» Enough sensitivity and resolving power to study the early universe through source counts
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Westerbork: 1970 Hogbom (Cambridge)
+ Christiansen (Sydney)
Benelux cross WSRT 12 x 25m dishes
– Two moveable– 10 redundant spacings– Self calibration
Add 2 more 25m dishes later
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LOFAR: The Low Frequency Array
Oort Workshop 1997 George Miley proposal to ASTRON Arnold van Ardenne already
thinking about SKA-low and the aperture arrays
Actively promoted by George– Low Frequencies are Cheap!
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LOFAR WILL EXPLORE NEW PARAMETER SPACE• Lowest Radio Frequencies (< 50 MHz) (Wavelengths > 3 metre)
– Neglected cradle of radio astronomy• Bill Erickson – a hero
– Coherent radiation processes– Oldest synchrotron electrons – “Fossil”– Absorption
• Huge Simultaneous Fields (tens of degrees with large-sky monitor triggering)– Searches for rare variable and transient sources and cosmic air showers– “Synoptic” telescope
• High Dynamic Range Radio Spectroscopy at 110 – 230 MHz– Search for fingerprint of reionization
• Neutral hydrogen (HI) at z ~ 11 to z ~7
DESIGN OF LOFAR DRIVEN BY FEW KEY PROJECTS
George MileyTasmania 2008
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16June 2013 Ekers, Radio Sources & Society
From Cambridge to The Netherlands 1970then to Australia 1996
Steven Hawking: black holes radiate Small black holes evaporate in less than the age
of the Universe Martin Rees: a radio pulse might be observable
when they disappear John O’Sullivan: and collaborators build a
special instrument to look for the exploding black holes using Dwingeloo and Westerbork – “there has to be a better way!”
Fourier Transform on a chip– IEEE 802.11 wireless internet standard
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Cygnus Astrongest radio source in sky
Hey 1946 – source with variable intensity– time scale of seconds to minutes– must be small diameter– the first “radio star”
What was it?– no optical counterpart– was the whole galactic plane was made of such stars?– no theory linking diffuse galactic emission to cosmic
rays
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What is the Non-thermal Radio Emission?
A very confusing story Misinterpretation of radio data added to the confusion some radio sources had small diameter (Hey).
– Hey was correct but it was incorrectly assumed that all radio emission was the sum of these radio stars
It was assumed that the radio stars were like the sun– this was also incorrect.– they were galactic nebula (SNR) and extra galactic
(AGN)
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Cliff Interferometer 1948
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Dover Heights, Sydney, Australia Piha and Leigh, New Zealand
Cliff interferometer CSIRO, Australia - NZ (1948)Built to identify the radio stars (John Bolton)Identification of the Crab Nebula super novae remnantDiscovery of extragalactic radio sources at great distances
Centaurus A – NGC5128 and Virgo A – M87
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NGC5128
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Centaurus A
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Centaurus AATCA MosaicFeain et al 2011
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The First Radio Galaxies
1949 : The first radio galaxies? “Positions of Three Discrete Sources of Galactic
Radio-Frequency Radiation” - (Bolton, Stanley, and Slee, Nature 164, 101)» NGC 5128 and NGC 4486 (M87) have not been
resolved into stars, so there is little direct evidence that they are true galaxies. If the identification of the radio sources are accepted, it would indicate that they are within our own Galaxy.
January 7, 2013 Kellermann AAS Long Beach
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Why was it so difficult to accept extra-galactic?
Letter from Bolton to Minkowski 20 May 1949
There were no galaxy experts at CSIR and very few in Australia
It was easier to assume that the strange galaxies were unusual galactic objects
There were no known mechanisms to explain the powerful radio emission if extragalactic
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Synchrotron Model for Radio Emission
1949 Unsold: sunspots anomalous radiation – non-thermal– plasma oscillations
1950 Alven & Herlofson: – synchrotron radiation from sunspots
1950 Kiepenhauer (visiting Yerkes)– proposed the ISM rather than stars– needed magnetic field and high energy charged particles– He knew there was evidence for both
» optical polarization and cosmic rays Mostly ignored in the West but enthusiastically embraced in
Russia by Ginzburg and later by Shklovski
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3C 48, the first radio star
Small diameter source catalogue from Manchester– Henry Palmer & George Miley ?
Accurate position measured at OVRO 1960 Tom Matthews and John Bolton
identify 3C 48 with a stellar object Greenstein, Munch, Sandage 200” spectra
– Lots of unidentified spectral lines Alan Sandage AAS paper (Dec 29, 1960),
– Remote possibility that it may be a distant galaxy of stars. But there is general agreement … that it is a relatively nearby star. S&T, 21, l48
January 7, 2013 Adapted from Kellermann AAS Long Beach
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3C 273 identification
January 7, 2013 Kellermann AAS Long Beach
Cyril HazardParkes lunar occultation
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AAS Long Beach 28
50th Anniversary of the Discovery of Quasars
January 7, 2013 Mt Palomar 200”
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3C273 Parkes Occultation 1962
Striking difference in radio spectra
Component A S = -0.9
Component B S = 0.0
Core – Jet morphology
Slide prepared by Jan Oort
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3C273VLA 5GHz 1998
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3C273Optical HST
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First Texas Symposium onRelativistic Astrophysics
Gravitational Collapse and Relativistic Astrophysics– Dallas, Texas, Dec 16-18 1963 – only gravity of a massive object in the
nucleus of a galaxy could provide the energy
Fred Hoyle: – relativists with their sophisticated work
were not only magnificent cultural ornaments but might actually be useful to science!
– The University of Chicago Press, 1965
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The Nuclei of Galaxies
1943: Carl Seyfert (Clevland, Ohio)– “Enhanced activity in the nuclei of 6
extragalactic nebulae– No citations for 18 years!
1958: Viktor Ambartsumian (Armenia)– Championed the role of the galaxy nuclei
1961: Vitaly Ginzburg (Russia)– Showed that gravitational energy could
power a radio galaxy
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The Energy Source Old models disappear fairly quickly
– Galaxies in collision (Baade & Minkowski) Bad theory– Nuclear energy– Electromagnetic flares
Redshift controversy lasts for many years– Many argued that the quasars are nearby Bad theory– New physics was better than the incredible luminosity– But all predictions failed
Gravitational energy from a collapsed object– Ginzburg, Hoyle, Fowler, Zeldovich, Novikov.....– This was a paradigm shift– But what kind of condensed object?
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Black Holes Chandrasekhar (1931) – paper rejected by ApJ
– “A star of large mass cannot pass into the white dwarf stage, one is left speculating on other possibilities”
Eddington – the authority– “a star would have to go on radiating and radiating, and
contracting and contracting….I think there should be a law of nature to stop matter behaving in this absurd way”
Oppenheimer (1939) – exercise in abstraction– “the star closes itself off from any communication…only
its gravitational field persists”
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NGC326 – pressing jetBinary Black hole?
Martin Rees 1978– One black hole already
pushes credibility – two was a step too far
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NGC326 – pressing jetBinary Black Hole?
Martin Rees 1978– One black hole already
pushes credibility – two was a step too far
Binary Black holes?– Evidence for super massive
binary black hole mergers and Gravitational wave predictions
Murgia et al, A&A 380, 102-116 (2001)Merritt & Ekers Science (2002)
VLA 1.4GHz
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Suspected SMBH binaries
3C75-type sources: wide binaries
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Periodic outbursts interpreting Pks0637-752
Binary black-hole in bound orbit periodicly plunges through the accretion disk
– will maintain its spin axis so gets a new accretion disk each plunge
PKS0637-752 – Quasar with Xray/radio jet
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Hercules A VLA and HST
Baum et al (2012)
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NGC1265 head tail radio source
• Head tail radio source• Rosetta stone for radio
galaxies- Provided the time stamp- Radio source aging
model was incorrect- Fixed by re-acceleration
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Fornax A on optical image
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Fornax A Depolarization
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Nov 2010 Ron Ekers
Fornax A and the ant like feature
Need a turbulant magneto-ionic medium RM > 20 rad m-2
Size 14” Eg
– Ne = .03 cm-3
– B = 2 μG – L = 100pc– M = 109 Mo
Bland-Hawthorne ApJ 447, L77 (1995)– Halpha detection at v = 1610km/s
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NGC6251Alignment
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VLBI cores aligned to within a few degrees over scale changes of 5x106
Hence maintains axis for at least 108 years
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3C273 superluminal expansionpredicted & observed
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Relativistic outflow in AGNM87
• One sided Doppler boost but components have v/c < 1 !
• components are slow moving shocks not measuring bulk flow
• evidence for original interpretation is now lost!
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HIPASS 21cm Continuum
Preliminary continuum image, courtesy Mark Calabretta (CSIRO ATNF)
Centaurus A - closest AGN
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Centaurus AATCA Mosaic
600kpc
1.4GHz continuum full polarization4 x 750m array
configuration406 pointings, hexagonal
gridFOV 45 deg2
θ~45’’ ~0.26mJy/beam (0.1K)
Ilana Feain
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Cen A Mosaic N lobe
May 2012 50
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Centaurus A composite
May 2012 51
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Centaurus A middle lobeX-ray XMM Newton
May 2012 52
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Centaurus A middle loberadio continuum and HI
May 2012 53
Morganti
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H alpha
May 2012 54
Ellis and Bland-Hawthorne
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LOFAR SCIENCE DRIVER 2: SURVEYS2.1 ULTRA STEEP SPECTRUM SOURCES –
PROBE OF GALAXY AND CLUSTER FORMATION e.g. Blumenthal & Miley 1988
Radio spectrumCygnus A
Larger redshifts > higher frequencies > steeper spectraLOFAR WILL DETECT STEEPEST SPECTRA
(MOST DISTANT SOURCES)
e.g. Blumenthal & Miley 1988
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The evolution of radio galaxiesBIG BANG
NOW
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July 2005 Ilana Klamer - ASA 57
our ATCA observations confirm that high-z radio galaxy spectra are not curved
but USS spectra don’t steepen at all…
The K-correction interpretation is inconsistent with observations
Klamer (Feien) MNRAS (2006)
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27 Nov 1999 R D Ekers 58
Evolution of density fluctuations
z=6 z=0
ρ (1+z)3
Δρ ρclusρ=0
ρ=0
ρ ≈ const
ρ ≈ const
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R D Ekers 5913 July 05
Radio Galaxy - 4C41.17redshift 3.8
Alignment of radio jets (contours) with other tracers of star formation– VLA radio image
HST F702
HST F569
Ly-α van Breugel (1985)
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R D Ekers 6013 July 2005
Klamer et al. 2004
Radio PA Dust PA CO PA
Alignment with Radio Axis
Predicted an alignment in 4C41.17Observed Δpa = 8o
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Survey of CO in High z Radio Galaxies
13 high redshift radio galaxies– 1.4 < z < 2.8
CO (1-0) aligned with radio axis!Emonts, Miley et al 2013
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Conclusion
March 2013
The power of science is its ability to make predictions
but science itself will evolve in unpredictable ways