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We investigate the clustering of galaxies selected in the 3.6 μm band of the Spitzer Wide-area Infrared Extragalactic (SWIRE) legacy survey. The angular two-point correlation function is calculated for 11 samples with flux limits of S3.6≥ 4–400 μJy, over an 8 deg2 field. The angular clustering strength is measured at >5σ significance at all flux limits, with amplitudes of A= (0.49–29) × 10−3 at 1°, for a power-law model, Aθ−0.8. We estimate the redshift distributions of the samples using phenomological models, simulations and photometric redshifts, and so derive the spatial correlation lengths. We compare our results with the Galaxies In Cosmological Simulations (GalICS) models of galaxy evolution and with parametrized models of clustering evolution. The GalICS simulations are consistent with our angular correlation functions, but fail to match the spatial clustering inferred from the phenomological models or the photometric redshifts. We find that the uncertainties in the redshift distributions of our samples dominate the statistical errors in our estimates of the spatial clustering. At low redshifts (median z≤ 0.5), the comoving correlation length is approximately constant, Mpc, and then decreases with increasing redshift to a value of 2.9 ± 0.3 h−1 Mpc for the faintest sample, for which the median redshift is z∼ 1. We suggest that this trend can be attributed to a decrease in the average galaxy and halo mass in the fainter flux-limited samples, corresponding to changes in the relative numbers of early- and late-type galaxies. However, we cannot rule out strong evolution of the correlation length over . [ABSTRACT FROM AUTHOR]

Deep spectroscopy of the two Leiden-Berkeley Deep Survey mJy radio galaxies LBDS 53W069 and 53W091 has previously shown them to have old (≥3 Gyr) stellar populations at z ... 1.5. Here we present the results of Hubble Space Telescope (HST) observations with the Wide Field and Planetary Camera 2 (WFPC2) in F814W and with the Near-Infrared Camera and Multi-Object Spectrograph (NICMOS) in F110W. We find that 53W069 has a de Vaucouleurs r[sup 1/4] profile in both the F814W and F110W data, with a mean effective radius of 0.30 ± 0.06 arcsec (2.7 ± 0.5 kpc). The rest-frame U - B colour gradient is consistent with that of present-day ellipticals, requiring a stellar population of supersolar (3 Z...) metallicity that formed on a very short time-scale at high redshift (z > 5). 53W091 has a regular r[sup 1/4] profile in F110W with an effective radius of 0.32 ± 0.08 arcsec (2.9 ± 0.7 kpc). The F814W profile is more extended and is consistent with the presence of a blue exponential disc that contributes 20 ± 10 per cent of the flux within re. We find a rest-frame U - B colour gradient that is significantly larger than that observed in field ellipticals at z ≤ 1, implying a stellar population of mixed metallicity (1-3 Z...) that formed in a high-redshift rapid burst. We have compared these two LBDS radio galaxies with the Kormendy relations of ten 3CR radio galaxies at z ... 0.8 and a sample of cluster ellipticals at z ... 0.4. The LBDS galaxies follow the Kormendy relation for the more radio-luminous 3CR galaxies, assuming passive evolution of their stellar populations, although they are smaller than the 3CR galaxies whose mean effective radius is 12 kpc. Their sizes and radio luminosities are consistent with scaling relations applied to the 3CR galaxies, in which both radio power and effective radius scale with galaxy mass. Compared with the sample of cluster ellipticals, 53W069 and 53W091 lie well within the scatter of the Kormendy... [ABSTRACT FROM AUTHOR]

Focuses on the use of spectroscopy and broad-band photometric redshifts on the distribution of Hercules sample of millijansky radio sources. Evolution of luminosity functions; Measurement of the steep-spectrum quasars; Observation of the stellar structure.

The results are presented of an extensive programme of optical and infrared imaging of radio sources in a complete subsample of the Leiden–Berkeley Deep Survey. The LBDS Hercules sample consists of 72 sources observed at 1.4 GHz, with flux densities S[sub 1.4]⩾1.0 mJy, in a 1.2 deg[sup 2] region of Hercules. This sample is almost completely identified in the g, r, i and K bands, with some additional data available at J and H. The magnitude distributions peak at r≃22 mag, K≃16 mag and extend down to r≃26 mag, K≃21 mag. The K-band magnitude distributions for the radio galaxies and quasars are compared with those of other radio surveys. At S[sub 1.4 GHz]≲1 Jy, the K-band distribution does not change significantly with radio flux density. The sources span a broad range of colours, with several being extremely red (r-K≳6). Though small, this is the most optically complete sample of mJy radio sources available at 1.4 GHz, and is ideally suited for studying the evolution of the radio luminosity function out to high redshifts. [ABSTRACT FROM AUTHOR]

We present the largest spectroscopic follow-up performed in SWIRE ELAIS-N1. We were able to determine redshifts for 289 extragalactic sources. The values of spectroscopic redshifts of the latter have been compared with the estimated values from our photometric redshift code with very good agreement between the two for both galaxies and quasars. Six of the quasars are hyperluminous infrared (IR) galaxies all of which are broad-line active galactic nuclei. We have performed emission-line diagnostics for 30 sources using the [O iii]/Hβ, [N ii]/Hα and [S ii]/Hα line ratios in order to classify these 30 sources into star forming, Seyferts, composite and LINER and compare the results to the predictions from our spectral energy distribution template fitting methods and mid-IR selection methods. [ABSTRACT FROM AUTHOR]

In a recent paper, Lehnert & Bremer have photometrically selected a sample of Lyman break galaxies at from a single VLT/FORS2 pointing and spectroscopically confirmed half of them to be at . To study the properties of such galaxies further, we have photometrically selected a similar sample from the Hubble Space Telescope Advanced Camera for Surveys ( HST ACS) images of the Chandra Deep Field-South. This selection results in a sample of 44 sources from . We find that such galaxies are often barely resolved in the ACS images, having half-light radii of 0.1–0.3 arcsec (<2 kpc). They show no difference in spatial clustering from sources selected by , which are generally galaxies of lower redshift. However, their distribution over the field is not uniform and their surface density varies considerably over areas comparable to a single 8-m or HST pointing. A reliable determination of the surface and volume densities of such galaxies requires a sky area considerably larger than the current ACS imaging of this field. No individual Lyman break candidate was detected to a 3σ limit of at 0.5–5 keV by Chandra (a limiting luminosity of below at ). By summing over all positions, we find that the mean source must be undetected at a level at least a factor of 4 times fainter than this. This rules out anything other than a weak active galactic nucleus (AGN) contribution to the emission from these objects; we conclude that luminous AGNs made little contribution to the final stages of re-ionization of the Universe. [ABSTRACT FROM AUTHOR]

We present the optical-to-submillimetre spectral energy distributions (SEDs) for 33 radio and mid-infrared (mid-IR) identified submillimetre galaxies discovered via the SHADES 850-μm SCUBA imaging in the Subaru- XMM Deep Field (SXDF). Optical data for the sources come from the SXDF and mid- and far-IR fluxes from SWIRE. We obtain photometric redshift estimates for our sources using optical and IRAC 3.6- and 4.5-μm fluxes. We then fit SED templates to the longer wavelength data to determine the nature of the far-IR emission that dominates the bolometric luminosity of these sources. The IR template fits are also used to resolve ambiguous identifications and cases of redshift aliasing. The redshift distribution obtained broadly matches previous results for submillimetre sources and on the SHADES SXDF field. Our template fitting finds that active galactic nuclei, while present in about 10 per cent of our sources, do not contribute significantly to their bolometric luminosity. Dust heating by starbursts, with either Arp220 or M82 type SEDs, appears to be responsible for the luminosity in most sources (23/33 are fitted by Arp220 templates, 2/33 by the warmer M82 templates). 8/33 sources, in contrast, are fitted by a cooler cirrus dust template, suggesting that cold dust has a role in some of these highly luminous objects. Three of our sources appear to have multiple identifications or components at the same redshift, but we find no statistical evidence that close associations are common among our SHADES sources. Examination of rest-frame K-band luminosity suggests that ‘downsizing’ is underway in the submillimetre galaxy population, with lower redshift systems lying in lower mass host galaxies. Of our 33 identifications six are found to be of lower reliability but their exclusion would not significantly alter our conclusions. [ABSTRACT FROM AUTHOR]

We analyse the first publicly released deep field of the UK Infrared Deep Sky Survey (UKIDSS) Deep eXtragalactic Survey to identify candidate galaxy overdensities at across ∼1 deg2 in the ELAIS-N1 field. Using and colours, we identify and spectroscopically follow up five candidate structures with Gemini/Gemini Multi-Object Spectrograph and confirm that they are all true overdensities with between five and 19 members each. Surprisingly, all five structures lie in a narrow redshift range at , although they are spread across 30 Mpc on the sky. We also find a more distant overdensity at in one of the spectroscopic survey regions. These five overdense regions lying in a narrow redshift range indicate the presence of a supercluster in this field and by comparing with mock cluster catalogues from N-body simulations we discuss the likely properties of this structure. Overall, we show that the properties of this supercluster are similar to the well-studied Shapley and Hercules superclusters at lower redshift. [ABSTRACT FROM AUTHOR]

We present details of the discovery of XLSS J022303.0−043622, a cluster of galaxies. This cluster was identified from its X-ray properties and selected as a candidate from its optical/near-infrared (IR) characteristics in the XMM Large-Scale Structure Survey ( XMM-LSS). It is the most distant system discovered in the survey to date. We present ground-based optical and near-IR observations of the system carried out as part of the XMM-LSS survey. The cluster has a bolometric X-ray luminosity of , fainter than most other known X-ray selected clusters. In the optical it has a remarkably compact core, with at least a dozen galaxies inside a 125 kpc radius circle centred on the X-ray position. Most of the galaxies within the core, and those spectroscopically confirmed to be cluster members, have stellar masses similar to those of massive cluster galaxies at low redshift. They have colours comparable to those of galaxies in other clusters, consistent with showing little sign of strong ongoing star formation. The bulk of the star formation within the galaxies appears to have ceased at least 1.5 Gyr before the observed epoch. Our results are consistent with massive cluster galaxies forming at and passively evolving thereafter. We also show that the system is straightforwardly identified in Spitzer/IRAC 3.6- and 4.5-μm data obtained by the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey emphasizing the power and utility of joint XMM and Spitzer searches for the most distant clusters. [ABSTRACT FROM AUTHOR]

We present the rest-frame optical and infrared colours of a complete sample of galaxies from the Spitzer Wide-Area Infrared Extragalactic (SWIRE) Legacy Survey and the Sloan Digital Sky Survey (SDSS). We discuss the optical and infrared colours of our sample and analyse in detail the contribution of dusty star-forming galaxies and active galactic nuclei (AGN) to optically selected red sequence galaxies. We propose that the optical colour and infrared colour of galaxies in our sample are determined primarily by a bulge-to-disc ratio. The colour is found to be sensitive to the bulge-to-disc ratio for disc-dominated galaxies, whereas the colour is more sensitive for bulge-dominated systems. We identify ∼18 per cent (195 sources) of our sample as having red optical colours and infrared excess. Typically, the infrared luminosities of these galaxies are found to be at the high end of star-forming galaxies with blue optical colours. Using emission-line diagnostic diagrams, 78 are found to have an AGN contribution and 117 are identified as star-forming systems. The red colour of the star-forming galaxies could be explained by extinction. However, their high optical luminosities cannot. We conclude that they have a significant bulge component. The number densities of optically red star-forming galaxies are found to correspond to ∼13 per cent of the total number density of our sample. In addition, these systems contribute ∼13 per cent of the total optical luminosity density, and 28 per cent of the total infrared luminosity density of our SWIRE/SDSS sample. These objects may reduce the need for ‘dry mergers’. [ABSTRACT FROM AUTHOR]