Publications (2)0 Total impact
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Chris Simpson,
Steve Rawlings,
Rob Ivision,
Masayuki Akiyama,
Omar Almaini,
Emma Bradshaw,
Scott Chapman, Rob Chuter,
Scott Croom,
Jim Dunlop,
Sebastien Foucaud,
Will Hartley
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ABSTRACT: We present spectroscopic and eleven-band photometric redshifts for galaxies
in the 100-uJy Subaru/XMM-Newton Deep Field radio source sample. We find good
agreement between our redshift distribution and that predicted by the SKA
Simulated Skies project. We find no correlation between K-band magnitude and
radio flux, but show that sources with 1.4-GHz flux densities below ~1mJy are
fainter in the near-infrared than brighter radio sources at the same redshift,
and we discuss the implications of this result for spectroscopically-incomplete
samples where the K-z relation has been used to estimate redshifts. We use the
infrared--radio correlation to separate our sample into radio-loud and
radio-quiet objects and show that only radio-loud hosts have spectral energy
distributions consistent with predominantly old stellar populations, although
the fraction of objects displaying such properties is a decreasing function of
radio luminosity. We calculate the 1.4-GHz radio luminosity function (RLF) in
redshift bins to z=4 and find that the space density of radio sources increases
with lookback time to z~2, with a more rapid increase for more powerful
sources. We demonstrate that radio-loud and radio-quiet sources of the same
radio luminosity evolve very differently. Radio-quiet sources display strong
evolution to z~2 while radio-loud AGNs below the break in the radio luminosity
function evolve more modestly and show hints of a decline in their space
density at z>1, with this decline occurring later for lower-luminosity objects.
If the radio luminosities of these sources are a function of their black hole
spins then slowly-rotating black holes must have a plentiful fuel supply for
longer, perhaps because they have yet to encounter the major merger that will
spin them up and use the remaining gas in a major burst of star formation.
01/2012;
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William Hartley,
Omar Almaini,
Michele Cirasuolo,
Sebastien Foucaud,
Chris Simpson,
Christopher Conselice,
Ian Smail,
Ross McLure,
Jim Dunlop, Rob Chuter,
Steve Maddox,
Kyle Lane,
Emma Bradshaw
[show abstract]
[hide abstract]
ABSTRACT: We use the UKIDSS Ultra-Deep Survey to trace the evolution of galaxy
clustering to z = 3. Using photometric redshifts derived from data covering the
wavelength range 0.3 - 4.5 um we examine this clustering as a function of
absolute K-band luminosity, colour and star-formation rate. Comparing the
deprojected clustering amplitudes, we find that red galaxies are more strongly
clustered than blue galaxies out to at least z = 1.5, irrespective of
rest-frame K-band luminosity. We then construct passive and star-forming
samples based on stellar age, colour and star-formation histories calculated
from the best fitting templates. The clustering strength of star-forming
galaxies declines steadily from r_0 ~ 7 h^-1 Mpc at z ~ 2 to r_0 ~ 3 h^-1 Mpc
at z ~ 0, while passive galaxies have clustering strengths up to a factor of
two higher. Within the passive and star-forming subsamples, however, we find
very little dependence of galaxy clustering on K-band luminosity. Galaxy
`passivity' appears to be the strongest indicator of clustering strength. We
compare these clustering measurements with those predicted for dark matter
halos and conclude that passive galaxies typically reside in halos of mass M >
10^13 M_sun while luminous star-forming galaxies occupy halos an order of
magnitude less massive over the range 0.5 < z < 1.5. The decline in the
clustering strength of star-forming galaxies with decreasing redshift indicates
a decline in the hosting halo mass for galaxies of a given luminosity. We find
evidence for convergence of clustering in star-forming and passive galaxies
around z ~ 2, which is consistent with this being the epoch at which the red
sequence of galaxies becomes distinct.
05/2010;
