We present the results of a new search for bright star-forming galaxies at redshift z 7 within the UltraVISTA DR2 and UKIDSS UDS DR10 data, which together provide 1.65 deg 2 of near-infrared imaging with overlapping optical and Spitzer data. Using a full photometric-redshift analysis to identify high-redshift galaxies and reject contaminants, we have selected a sample of 34 luminous (−22.7 < M U V < −21.2) galaxies with 6.5 < z < 7.5. Crucially, the deeper imaging provided by UltraVISTA DR2 confirms all of the robust objects previously uncovered by Bowler et al. (2012), validating our selection technique. Our new expanded galaxy sample includes the most massive galaxies known at z 7, with M 10 10 M , and the majority are resolved, consistent with larger sizes (r 1/2 1−1.5 kpc) than displayed by less massive galaxies. From our final robust sample, we determine the form of the bright end of the rest-frame UV galaxy luminosity function (LF) at z 7, providing strong evidence that it does not decline as steeply as predicted by the Schechter-function fit to fainter data. We exclude the possibility that this is due to either gravitational lensing, or significant contamination of our galaxy sample by active galactic nuclei (AGN). Rather, our results favour a double power-law form for the galaxy LF at high redshift, or, more interestingly, a LF which simply follows the form of the dark-matter halo mass-function at bright magnitudes. This suggests that the physical mechanism which inhibits starformation activity in massive galaxies (i.e. AGN feedback or some other form of 'mass quenching') has yet to impact on the observable galaxy LF at z 7, a conclusion supported by the estimated masses of our brightest galaxies which have only just reached a mass comparable to the critical 'quenching mass' of M 10 10.2 M derived from studies of the mass function of star-forming galaxies at lower redshift.

We present the first results from the Australia Telescope Large Area Survey, which consists of deep radio observations of a 3.7 deg 2 field surrounding the Chandra Deep Field-South, largely coincident with the infrared Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey. We also list cross-identifications to infrared and optical photometry data from SWIRE, and ground-based optical spectroscopy. A total of 784 radio components are identified, corresponding to 726 distinct radio sources, nearly all of which are identified with SWIRE sources. Of the radio sources with measured redshifts, most lie in the redshift range 0.5-2 and include both star-forming galaxies and active galactic nuclei. We identify a rare population of infrared-faint radio sources that are bright at radio wavelengths but are not seen in the available optical, infrared, or X-ray data. Such rare classes of sources can only be discovered in wide, deep surveys such as this.

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(Abridged) We examine the power source of 41 local Ultraluminous Infrared Galaxies using archival infrared and optical photometry. We fit the observed Spectral Energy Distributions (SEDs) with starburst and AGN components; each component being drawn from a family of templates. We find all of the sample require a starburst, whereas only half require an AGN. In 90% of the sample the starburst provides over half the IR emission, with a mean fractional luminosity of 82%. When combined with other galaxy samples we find that starburst and AGN luminosities correlate over 6 decades in IR luminosity suggesting that a common factor governs both luminosities, plausibly the gas masses in the nuclear regions. We find that the mid-IR 7.7 micron line-continuum ratio is no indication of the starburst luminosity, or the fractional AGN luminosity, and therefore that this ratio is not a reliable diagnostic of the power source in ULIRGs. We propose that the scatter in the radio-IR correlation in ULIRGs is due to a skewed starburst IMF and/or relic relativistic electrons from a previous starburst, rather than contamination from an obscured AGN. We show that most ULIRGs undergo multiple starbursts during their lifetime, and by inference that mergers between more than two galaxies may be common amongst ULIRGs. Our results support the evolutionary model for ULIRGs proposed by Farrah et al 2001, where they can follow many different evolutionary paths of starburst and AGN activity in transforming merging spiral galaxies into elliptical galaxies, but that most do not go through an optical QSO phase. The lower level of AGN activity in our local sample than in z~1 HLIRGs implies that the two samples are distinct populations. We postulate that different galaxy formation processes at high-z are responsible for this difference.Comment: 24 pages, 8 figures. Accepted for publication in MNRA