OBSERVING GALAXY CLUSTERS WITH NEXT GENERATION RADIO TELESCOPES Melanie Johnston-Hollitt Victoria University of Wellington

Radio Renaissance •  Radio astronomy is currently undergoing a renaissance in

terms of construction of new instruments and revitalization of high impact science goals

•  In the last decade a number of new radio telescopes have been constructed and older telescopes upgraded: •  International LOFAR Telescope (ILT) •  Jansky Very Large Array (JVLA) •  Australia Telescope Compact Array (ATCA) •  E-Merlin •  Australian SKA Pathfinder (ASKAP) •  Fiver Hundred Meter Aperture Synthesis Telescope (FAST) •  Westerbork Radio Synthesis Telescope (WRST) •  Murchison Widefield Array (MWA)

•  At the end of this next decade this will culminate in the Square Kilometre Array

Next Generation Radio Telescopes •  Many telescopes currently in construction leading up to the SKA. •  We’ve heard a lot about LOFAR, here I want to focus on ASKAP &

MWA and then finally comment on SKA. •  ASKAP: 36 element PAF interferometer, 700 MHz -1.8 GHz (see

Johnston et al. (2008), Norris et al. (2011)) •  MWA: 128 ‘title’ dipole array, 80 – 300 MHz (see Tingay et al. (2013a),

Bowman et al. (2013))

ASKAP & MWA • ASKAP

•  36 PAF enabled antennas, 0.7 – 1.8 GHz range with 300 MHz band. 27 square degree FOV with up to 10” resolution.

• MWA •  128 tiles of 16 dipoles, 80 – 300 MHz range, ~30 MHz band. 30

square degree FoV with ~1.5’ – 2.5’ resolution in 2015 and hopefully 45” – 1.5’ resolution in late 2016 after addition of a further 128 tiles

•  Located at Murchison Radio Observatory (MRO) which is a protected radio quiet zone in Western Australia.

•  Two surveys of interest to people working on clusters: ASKAP-EMU & MWA’s GLEAM. EMU is a future survey, GLEAM is nearly completed.

EMU • Evolutionary Map of the Universe – will be a continuum

radio survey on ASKAP at 1.4 GHz.

•  The aim is to achieve 10uJy rms and 10” resolution hopefully with an option for 25-30” tapered images also.

•  First observations on a test array of 12 antennas scheduled later this year.

• EMU is an open collaboration. PI is Ray Norris, but if you want to join, let me know. We are soliciting early science ideas now.

Example of EMU-like Science •  The ATCA can now achieve 10 uJy/b 10” resolution

images which are thus analogous to EMU. Here I show an example of the kind of thing that can be done with such an instrument.

• Will examine PLCK G285.0-23.7 (z=0.38) work done by Gerardo Martinez Aviles & MJH. X-ray & SZ courtesy of Gabriel Pratt & Nabila Aghanim. Collaborators Tiziana Venturi, Gianfranco Brunetti, Rossella Cassano (all present) and Chiara Ferrari…

•  To appear in Martinez Aviles et al. hopefully soon.

Field of PLCK G285.0-23.7 5” at 2.1 GHz, 11 uJy/b

Field of PLCK G285.0-23.7 20” taper applied Radio halo appears ~950 x 470 kpc

Clearly a merging cluster yet doesn’t sit on the Cassano et al. correlation. We have investigated effects of redshift and there seems to be evidence that the correlation is evolving beyond z = 0.35. Full analysis in Martinez Aviles et al. (in prep)

EMU will fill this part of the box

GLEAM Survey • GaLactic and Extragalactic All-sky MWA Survey

•  M. Bell, J. Callingham, K.S. Dwarakanath, B-Q. For, B. Gaensler, P. Hancock, L. Hindson, N. Hurley-Walker, M. Johnston-Hollitt, A. Kapinska, E. Lenc, B. McKinley, J. Morgan, A. Offringa, P. Procopio, L. Staveley-Smith, R. Wayth, C. Wu, Q. Zheng

•  5 x 32 MHz frequencies of the entire sky south of +30 degrees.

• Covers 72 to 231 MHz down to the confusion limit (5 – 60 mJy)

• Excellent short spacing uv-coverage -> important for diffuse emission.

• Complementary to MSSS (Heald et al. submitted) in point source sensitivity.

GLEAM Sky Coverage • All observations completed, phase I data processing done

& phase II on going.

Clusters in GLEAM •  Due to low resolution,

although it is possible to detect diffuse cluster emission in distant clusters in GLEAM, you need ancillary higher resolution data to confirm it.

•  So, first look has been at larger nearby clusters.

•  Selected all clusters in the MCXC with R500 > 15’

•  Sample of 105 clusters, but only 67 have been processed.

CL 2020-5535 z=0.2320

MWA 150 MHz

ATCA 2.1 GHz

SUMSS 0.8 GHz Zheng et al. (in prep)

Sample of nearby clusters

• Spans redshift up to ~0.07 and most are within 43 < Log(Lx) <45.

Diffuse emission • Diffuse emission is detected in 12/67 clusters (18%)

including several new halos and possible relics.

• Detection rate is similar to extended GMRT sample (Kale, Venturi et al.)

• Additionally, diffuse emission detected in GLEAM for unknown clusters is much larger than that in the current literature.

•  I’ll show three examples: •  A3667,

•  A754and

•  A3376.

Hindson, Johnston-Hollitt et al. 2014

Hindson, Johnston-Hollitt et al. 2014

Spectral Index • Both relics

suggest shocks of 2.4 +/- 0.4 which are consistent with the value derived from X-ray.

Hindson, Johnston-Hollitt et al. 2014

GLEAM 150 MHz Naturally Weighted, so Galactic emission Suppressed but needs to still be separated via spectral index mapping. RMS = 11 mJy/b 2.5’ beam

New SNR

Hydra A

A754

30 deg GLEAM 150 MHz 6mJy/b ~2.5 arcmin

1.4 GHz VLA at 70” resolution Macario et al. 2011

150 MHz GLEAM RMS = 9 mJy/b ~2.5’ resolution

A3376 •  Little known fact;

double relic first noted in the honours (MSc) thesis of Tara Murphy, University of Sydney, 1999 from her search of SUMSS. Independently rediscovered by Bagchi 2002 using NVSS.

•  z=0.0467

•  XMM, ATCA, AAO campaign undertaken from 2004 – 2006.

Optical Galaxy Distribution • Spectroscopic

observations undertaken in December 2004 to map the cluster. Right is the optical isodensity for confirmed spectroscopic cluster members

• Note filaments…

GLEAM 150 MHz RMS 4 mJy/b

Results • GLEAM is seeing similar detection rates for diffuse

emission as other dedicated studies but GLEAM is detection larger diffuse emission than all other work.

• We have the first detection of diffuse radio emission associated with a filament in the cosmic web.

•  There are other examples in GLEAM which I haven’t shown and am in the process of verifying spectroscopically.

• Next few years both GLEAM and EMU will have a huge impact on cluster science.

• Beyond that we have SKA1_LOW and SKA1_MID with the possible continuance of ASKAP.