Galaxy Cluster Science in with EMU

Galaxy Cluster Science in with EMU
Understanding the Role of Environment on Radio Emission
in Clusters of Galaxies
Dr Melanie Johnston-Hollitt,
Victoria University of Wellington
Heinz Andernach, Annalisa Bonafede, Shea Brown, Gianfranco Brunetti, Rosella Cassano, Tracy Clarke,
Warrick Couch, Siamak Dehghan, Jose Diego, Luigina Feretti, Chiara Ferrari, Gabriele Giovannini,
Antony Gomez, Peter Jensen, Giulia Macario, Ray Norris, Paul Nulsen, Matt Owers, Kevin Pimbblet,
Gabriel Pratt, Thomas Reiprich, Larry Rudnick, Huub Rottgering, Sara Shakouri, Tizianna Venturi,
Michael Wise
A2199: 1.2m Whipple Obs.
Virgo Consortium
Stephan’s Quintet NASA/JPL-Caltech/Max Planck Institute
Galaxy Clusters with ASKAP
  EMU
Will detect radio synchrotron
emission in clusters & filaments on all scales.
  POSSUM Will probe the polarisation of EMU
sources including rotation measures.
  WALLABY will perform a deep HI survey of
the sky detecting 500,000 galaxies to z
=0.26.
  The best cluster science will be achieved by
combining data from these (and other)
surveys eg WODAN, LOFAR etc.
Radio Observations of Clusters
A3667: Johnston-Hollitt (2003)
• 
Muxlow et al. (2005)
Head-tail in A3125:
Johnston-Hollitt et al. (2004),
Mao et al. (2009)
Three main types of
continuum emission in
clusters
– Cluster wide emission
(relics & halos)
– Individual galaxies
powered by AGN
(head-tailed galaxies)
– Star formation
Cluster Eco-system
Filament
Star forming galaxies
Cluster
Halo
Head-tail Galaxy
“Normal” galaxies
Relics
Original cartoon from NASA/JPL-Caltech: modified by MJH
EMU Key Science Goals
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To trace the evolution of star-forming galaxies from z=2 to
the present day, using a wavelength unbiased by dust or
molecular emission.
To trace the evolution of massive black holes throughout the
history of the Universe, and understand their relationship to
star-formation.
To use the distribution of radio sources to explore the largescale structure and cosmological parameters of the Universe.
To explore an uncharted region of observational parameter
space, almost certainly finding new classes of object.
To determine how radio sources populate dark matter halos,
providing crucial insights into the underlying astrophysics of
clusters and halos.
To create the most sensitive wide-field atlas of Galactic
continuum emission yet made in the Southern Hemisphere,
addressing areas such as star formation, supernovae, and
Galactic structure.
Relic & Halo studies
Star formation studies
EMU Cluster Science (part 1)
 
Multivariate analysis on cluster merger state & environmental
conditions versus SF rate in the local (z< 0.1) universe ie do mergers
induce star-formation? At what point in the merger history does this
occur? How does the richness of the environment affect the results?
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The first statistically significant study of the radio Butcher-Oemler
effect in clusters out to z = 0.3 ie how does the radio-detected SF rate
in clusters evolve with redshift?
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A first detailed investigation of the star-forming history of cluster
filaments.
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Blind detection of radio halos in greater numbers allowing unbiased
tests on their generation and presumed correlation with X-ray
luminosity and constraints on the turbulence and magnetic fields in
clusters to be determined.
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Blind detection of accretion shocks and radio relics in greater numbers
allowing unambiguous signposts of merging to be detected, the first
relic luminosity function to be calculated and constraints on the
turbulence and magnetic fields in clusters to be determined.
EMU Cluster Science (part 2)
Detection of diffuse sources in cluster filaments.
The first investigation of a large sample of bent
double radio galaxies in terms of environmental
conditions and potentially the use of such probes
to detect new galaxy clusters out to z = 1.
  Calculation of a new cluster Radio Luminosity
Function for both early and late-type galaxies.
  An examination of Low luminosity radio galaxies
and AGN feedback.
  Cluster detection from radio observations with
EMU as comparison to other wavelengths such as
X-ray.
  Source detection algorithms.
AGN studies
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What do we use now?
Indicators of Cluster Environment & Evolution
Radio
Optical
X-ray
Extended Radio Sources
(Head-tailed galaxies,
halos, relics)
Morphology
Pressure &
Temperature
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Redshift
Distribution
Spatial
Distribution
Morphology
Polarisation
Spectral
Index
Source counts
& Luminosity
Functions
At present it’s difficult to detect clusters without
optical or X-ray surveys. These are expensive.
It is also difficult to characterise cluster
environmental conditions with radio alone.
In the future a large, deep radio survey like EMU
might do a much better job very cheaply…
Evolutionary Map of the Universe:
EMU
  EMU
~10µJy rms, 10” resolution, entire
Southern Sky (dec < +30°)
  “Southern NVSS”, except ~40 times the
sensitivity
  Able to probe star forming galaxies up to
z=1, AGNs to the edge of the Universe.
  SF rate: 100s of
Mo/yr to z ~ 1
and few Mo to
z > 0.3
Radio galaxy population studies
  How
does environment affect the radio
galaxy population in clusters & filaments?
◦  Do mergers induce star-formation?
◦  At what point in the merger history does this
occur?
◦  How does the richness of the environment
affect the results?
◦  How does the radio-detected SF rate in
clusters evolve with redshift?
Sensitivity issues now
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Cluster source counts to date mainly probing AGN; due
to lack of sensitivity
SF
AGN
SF
AGN
Source counts for parts of Shapley concentration (Venturi et al. 1999 - 2001)
overlaid with line representing background counts (Prandoni et al. 2001).
EMU gives Leap forward in sensitivity
– shows faint radio ‘species’
Sensitivity
increase to 10 µJy
with improved uvcoverage means
we can probe the
radio source
population across
clusters and
superclusters over
the whole sky.
  Probe both the
AGN & SF
population in
clusters
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Sadler et al. 2001
Merger suppression of AGN, tidal
starformation increase?
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Current literature suggests
that there is a strong
environmental dependence in
low z (> 0.1) clusters as to the
radio emissions seen with a
critical difference in AGN & SF
populations.
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Late stage mergers are
increasingly associated with
suppression of AGN (Venturi
et al. 2000, Johnston-Hollitt et
al. 2008)
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while at the same time we see
increased blue, low-powered
radio galaxies (Miller et al
2003 -2006, Johnston-Hollitt et
al. 2008) which are likely to be
tidally induced SF galaxies.
Johnston-Hollitt et al. 2008
Merger effects on radio galaxy
populations
Cluster
Source counts
Early type RLF
Merger stage
A3556
consistent
consistent
early
A3558
consistent
suppressed
late
A3528
consistent
consistent
early
A3571
consistent
suppressed
late
A3558 outskirts
consistent but weak excess
suppressed
late
A2125
excess low-power
Late; merging along axis of lowpower excess
A2255
excess low-power
late
A2111
excess low-power
?
excess low-power
merging along axis of low power
excess
A3158
suppressed
Radio as a probe for LSS
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Probing the faint end flux sources in clusters is
likely to result in detection of clusters as overdensities in the radio out to quite high redshifts ie
“as can use the distribution of sources to explore LSS
and cosmological parameters”.
A3128
15’ x 15’
DSS Blue
ATCA 1.4 GHz
Radio as a probe for LSS
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Probing the faint end flux sources in clusters is
likely to result in detection of clusters as overdensities in the radio out to quite high redshifts ie
“as can use the distribution of sources to explore LSS
and cosmological parameters”.
Optical image of the CDFS filed. Credit: NASA/
IPAC Infrared Science Archive
Radio image of the CDFS filed. Credit: Miller et al.
Radio as a probe for LSS
 
Probing the faint end flux sources in clusters is
likely to result in detection of clusters as overdensities in the radio out to quite high redshifts ie
“as can use the distribution of sources to explore LSS
and cosmological parameters”.
Optical image of the CDFS filed. Credit: NASA/
IPAC Infrared Science Archive
Radio image of the CDFS filed. Credit: Miller et al.
Radio as a probe for LSS
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At the level of EMU we find radio sources strongly correlated with overdensities.
Redshift information for this work is critical now but if you believe the
result then can do the radio/CMB correlation for cosmology.
Location of major radio sources in the CDFS field.
Credit: VUW Radio Astronomy Group.
3D map of the detected structures on the CDFS overlaid
on major radio sources in the CDFS field. Credit: VUW
Radio Astronomy Group.
Tailed radio galaxies: signposts to
high density environments
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S447 – most distant tailed source yet
detected at z ~1.98 (Dehghan et al.
2011)
Tailed radio galaxies (WATs,
NATs) have been shown to mark
the most dense regions in galaxy
clusters in the local (z <0.07)
Universe (Mao et al. 2009, Cropp
2010) and trace over-densities
out to redshifts approaching 2
(Dehghan et al. 2011).
Thus, tailed radio galaxies
discovered in EMU will be
valuable early indicators for sites
of mass concentration which can
then be compared with other
indicators such as clustering of
radio point sources, or optical/
X-ray data.
Tailed radio galaxies as barometers
of cluster weather
 
A lot of physics can be
done with tailed radio
galaxies – modeling
provides information on
the ICM including density,
B-field estimates (from
polarisation data).
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EMU will detect
somewhere between
30,000 & 100,000 tailed
radio galaxies which can
be used both to detect
overdensities and to then
probe conditions in such
places as a function of
cosmic time.
Composite Image of 1.4, 2.5, and 4.8GHz ATCA data
(orange) and a Digitized Sky Survey optical image
(white) of PKS J0334-3900, overlaid on the final
frame of the simulation showing 50Myr evolution of
this radio source assuming orbital motion of the
host galaxy around a companion together with a
cluster wind (Pratley et al. 2011).
Diffuse radio emission detection
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Potentially going to be hard to detect. Depends on how EMU
is processed. We might find ~4000 (cf ~50 now)
New techniques to find diffuse sources from images might be
required. A range of techniques being tested for EMU:
◦  Compressive sampling (Ferarri & Mary)
◦  Multi-scale filtering (Brown & Rudnick)
◦  Hough Transforms (Hollitt & Johnston-Hollitt)
A3667: Johnston-Hollitt (2003)
Examples of source detection with
CHT: Hollitt & Johnston-Hollitt (2009 & 2011)
Science Summary
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Different types of radio emission appear to trace different conditions
and dynamical states within galaxy clusters.
We are constrained by current sensitivity and missing large samples to
test the full range of correlations in the cluster ecology. EMU, in
combination with multiwavelength data, will do this.
=> with such correlations established we can do a census of the
dynamical state of clusters in the local Universe (z > 0.3) very cheaply.
LOTS of science to do we will be very busy over the next few years…
Filament
Star forming galaxies
Cluster
Head-tail Galaxy
“Normal” galaxies
Relics
Status of the EMU Cluster WG
  Lead
authors for the science paper have
been assigned – MJH will contact those
people mid-September to get an update.
  First full paper draft out by November.
  Final paper submitted to PASA at least
early 2012.
Thank you!
Virgo Consortium