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We present spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) 870 μm dust continuum maps of six massive, compact, dusty star-forming galaxies at z ∼ 2.5. These galaxies are selected for their small rest-frame optical sizes (reF160W ∼ 1.6 kpc) and high stellar mass densities that suggest that they are direct progenitors of compact quiescent galaxies at z ∼ 2. The deep observations yield high far-infrared (FIR) luminosities of LIR = 1012.3-12.8 L⊙ and star formation rates (SFRs) of SFR = 200-700 M o yr-1, consistent with those of typical star-forming "main sequence" galaxies. The high spatial resolution (FWHM ∼ 0.″12-0.″18) ALMA and Hubble Space Telescope photometry are combined to construct deconvolved, mean radial profiles of their stellar mass and (UV+IR) SFR. We find that the dusty, nuclear IR-SFR overwhelmingly dominates the bolometric SFR up to r ∼ 5 kpc, by a factor of over 100× from the unobscured UV-SFR. Furthermore, the effective radius of the mean SFR profile (re,SFR ∼ 1 kpc) is ∼30% smaller than that of the stellar mass profile. The implied structural evolution, if such nuclear starburst last for the estimated gas depletion time of Δt = ± 100 Myr, is a 4× increase of the stellar mass density within the central 1 kpc and a 1.6× decrease of the half-mass-radius. This structural evolution fully supports dissipation-driven, formation scenarios in which strong nuclear starbursts transform larger, star-forming progenitors into compact quiescent galaxies.

Chandra data in the COSMOS, AEGIS-XD and 4 Ms Chandra Deep Field South are combined with multiwavelength photometry available in those fields to determine the rest-frame U-V versus V-J colours of X-ray AGN hosts in the redshift intervals 0.1 < z < 0.6 (mean z = 0.40) and 0.6 < z < 1.2 (mean z = 0.85). This combination of colours provides an effective and least model-dependent means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasizes differences between AGN populations split by their U-V versus V-J colours. AGN in quiescent galaxies consist almost exclusively of bulges, while star-forming hosts are equally split between early-and late-type hosts. The position of AGN hosts on the U-V versus V-J diagram is then used to set limits on the accretion density of the Universe associated with evolved and star-forming systems independent of dust induced biases. It is found that most of the black hole growth at z ̃0.40 and 0.85 is associated with star-forming hosts. Nevertheless, a non-negligible fraction of the X-ray luminosity density, about 15-20 per cent, at both z = 0.40 and 0.85, is taking place in galaxies in the quiescent region of the U-V versus V-J diagram. For the low-redshift sub-sample, 0.1 < z < 0.6, we also find tentative evidence, significant at the 2σ level, that AGN split by their U-V and V-J colours have different Eddington ratio distributions. AGN in blue star-forming hosts dominate at relatively high Eddington ratios. In contrast, AGN in red quiescent hosts become increasingly important as a fraction of the total population towards low Eddington ratios. At higher redshift,z > 0.6, such differences are significant at the 2σ level only for sources with Eddington ratios ≥10-3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of supermassive black holes at the centres of galaxies.We compare these results with the predictions of the GALFORM semi-analytic model for the cosmological evolution of AGN and galaxies. This model postulates two black hole fuelling modes, the first is linked to star formation events and the second takes place in passive galaxies. GALFORM predicts that a substantial fraction of the black hole growth at z < 1 is associated with quiescent galaxies, in apparent conflict with the observations. Relaxing the strong assumption of the model that passive AGN hosts have zero star formation rate could bring those predictions in better agreement with the data. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Chandra data in the COSMOS, AEGIS-XD and 4 Ms Chandra Deep Field South are combined with multiwavelength photometry available in those fields to determine the rest-frame U-V versus V-J colours of X-ray AGN hosts in the redshift intervals 0.1 < z < 0.6 (mean z = 0.40) and 0.6 < z < 1.2 (mean z = 0.85). This combination of colours provides an effective and least model-dependent means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasizes differences between AGN populations split by their U-V versus V-J colours. AGN in quiescent galaxies consist almost exclusively of bulges, while star-forming hosts are equally split between early-and late-type hosts. The position of AGN hosts on the U-V versus V-J diagram is then used to set limits on the accretion density of the Universe associated with evolved and star-forming systems independent of dust induced biases. It is found that most of the black hole growth at z ̃0.40 and 0.85 is associated with star-forming hosts. Nevertheless, a non-negligible fraction of the X-ray luminosity density, about 15-20 per cent, at both z = 0.40 and 0.85, is taking place in galaxies in the quiescent region of the U-V versus V-J diagram. For the low-redshift sub-sample, 0.1 < z < 0.6, we also find tentative evidence, significant at the 2σ level, that AGN split by their U-V and V-J colours have different Eddington ratio distributions. AGN in blue star-forming hosts dominate at relatively high Eddington ratios. In contrast, AGN in red quiescent hosts become increasingly important as a fraction of the total population towards low Eddington ratios. At higher redshift,z > 0.6, such differences are significant at the 2σ level only for sources with Eddington ratios ≥10-3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of supermassive black holes at the centres of galaxies.We compare these results with the predictions of the GALFORM semi-analytic model for the cosmological evolution of AGN and galaxies. This model postulates two black hole fuelling modes, the first is linked to star formation events and the second takes place in passive galaxies. GALFORM predicts that a substantial fraction of the black hole growth at z < 1 is associated with quiescent galaxies, in apparent conflict with the observations. Relaxing the strong assumption of the model that passive AGN hosts have zero star formation rate could bring those predictions in better agreement with the data. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

We present evidence for a strong relationship between galaxy size and environment for the quiescent population in the redshift range 1 < z < 2. Environments were measured using projected galaxy overdensities on a scale of 400 kpc, as determined from ~96 000 K-bandselected galaxies from the UKIDSS Ultra Deep Survey (UDS). Sizes were determined from ground-based K-band imaging, calibrated using space-based CANDELS HST observations in the centre of the UDS field, with photometric redshifts and stellar masses derived from 11-band photometric fitting. From the resulting size-mass relation, we confirm that quiescent galaxies at a given stellar mass were typically ~50 per cent smaller at z ~ 1.4 compared to the present day. At a given epoch, however, we find that passive galaxies in denser environments are on average significantly larger at a given stellar mass. The most massive quiescent galaxies (Mz.ast; >2×1011M⊙) atz>1 are typically 50 per cent larger in the highest density environments compared to those in the lowest density environments. Using Monte Carlo simulations, we reject the null hypothesis that the size-mass relation is independent of environment at a significance >4.8s for the redshift range 1< z