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We compare the l-galaxies semi-analytic model to deep observational data from the UKIDSS Ultra Deep Survey (UDS) across the redshift range 0.5 < z < 3. We find that the overabundance of low-mass, passive galaxies at high redshifts in the model can be attributed solely to the properties of 'orphan' galaxies, i.e. satellite galaxies where the simulation has lost track of the host dark matter sub-halo. We implement a simple model that boosts the star formation rates in orphan galaxies by matching them to non-orphaned satellite galaxies at a similar evolutionary stage. This straightforward change largely addresses the discrepancy in the low-mass passive fraction across all redshifts. We find that the orphan problem is somewhat alleviated by higher resolution simulations, but the preservation of a larger gas reservoir in orphans is still required to produce a better fit to the observed space density of low-mass passive galaxies. Our findings are also robust to the precise definition of the passive galaxy population. In general, considering the vastly different prescriptions used for orphans in semi-analytic models, we recommend that they are analysed separately from the resolved satellite galaxy population, particularly with JWST observations reigniting interest in the low-mass regime in which they dominate. [ABSTRACT FROM AUTHOR]

We conduct the first study of how the relative quenching probability of galaxies depends on environment over the redshift range 0.5 < z < 3, using data from the UKIDSS Ultra Deep Survey. By constructing the stellar mass functions for quiescent and post-starburst (PSB) galaxies in high-, medium-, and low-density environments to z = 3, we find an excess of quenched galaxies in dense environments out to at least z ∼ 2. Using the growth rate in the number of quenched galaxies, combined with the star-forming galaxy mass function, we calculate the probability that a given star-forming galaxy is quenched per unit time. We find a significantly higher quenching rate in dense environments (at a given stellar mass) at all redshifts. Massive galaxies (M* > 1010.7 M⊙) are on average 1.7 ± 0.2 times more likely to quench per Gyr in the densest third of environments compared to the sparsest third. Finally, we compare the quiescent galaxy growth rate to the rate at which galaxies pass through a PSB phase. Assuming a visibility time-scale of 500 Myr, we find that the PSB route can explain ∼50 per cent of the growth in the quiescent population at high stellar mass (M* > 1010.7 M⊙) in the redshift range 0.5 < z < 3, and potentially all of the growth at lower stellar masses. [ABSTRACT FROM AUTHOR]

We present an analysis of the structure of post-starburst (PSB) galaxies in the redshift range 0.5 < $$z$$ < 2, using a photometrically selected sample identified in the Ultra Deep Survey field. We examine the structure of ∼80 of these transient galaxies using radial light μ(r) profiles obtained from CANDELS Hubble Space Telescope near-infrared/optical imaging, and compare to a large sample of ∼2000 passive and star-forming galaxies. For each population, we determine their typical structural properties (effective radius r e, Sérsic index n) and find significant differences in PSB structure at different epochs. At high redshift ($$z$$ > 1), PSBs are typically massive ($$M_* \gt 10^{10}\rm \, M_{\odot }$$), very compact and exhibit high Sérsic indices, with structures that differ significantly from their star-forming progenitors but are similar to massive passive galaxies. In contrast, at lower redshift (0.5 < $$z$$ < 1), PSBs are generally of low mass ($$M_* \lt 10^{10}\rm \, M_{\odot }$$) and exhibit compact but less concentrated profiles (i.e. lower Sérsic indices), with structures similar to low-mass passive discs. Furthermore, for both epochs, we find remarkably consistent PSB structure across the optical/near-infrared wavebands (which largely trace different stellar populations), suggesting that any preceding starburst and/or quenching in PSBs was not strongly centralized. Taken together, these results imply that PSBs at $$z$$ > 1 have been recently quenched during a major disruptive event (e.g. merger or protogalactic collapse) that formed a compact remnant, while at $$z$$ < 1 an alternative less disruptive process is primarily responsible. Our results suggest that high- $$z$$ PSBs are an intrinsically different population to those at lower redshifts, and indicate different quenching routes are active at different epochs. [ABSTRACT FROM AUTHOR]

We present a comparison of the observed evolving galaxy stellar mass functions with the predictions of eight semi-analytic models and one halo occupation distribution model. While most models are able to fit the data at low redshift, some of them struggle to simultaneously fit observations at high redshift. We separate the galaxies into 'passive' and 'star-forming' classes and find that several of the models produce too many low-mass star-forming galaxies at high redshift compared to observations, in some cases by nearly a factor of 10 in the redshift range 2.5 < $$z$$ < 3.0. We also find important differences in the implied mass of the dark matter haloes the galaxies inhabit, by comparing with halo masses inferred from observations. Galaxies at high redshift in the models are in lower mass haloes than suggested by observations, and the star formation efficiency in low-mass haloes is higher than observed. We conclude that many of the models require a physical prescription that acts to dissociate the growth of low-mass galaxies from the growth of their dark matter haloes at high redshift. [ABSTRACT FROM AUTHOR]

We present a large-scale galaxy structure Cl J021734-0513 at z~ 0.65 discovered in the UKIDSS UDS field, made of~20 galaxy groups and clusters, spreading over 10Mpc. We report on a VLT/VIMOS spectroscopic follow-up program that, combined with past spectroscopy, allowed us to confirm four galaxy clusters (M200~ 1014 M~) and a dozen associated groups and star-forming galaxy overdensities. Two additional filamentary structures at z~0.62 and 0.69 and foreground and background clusters at 0.6 < z < 0.7 were also confirmed along the line of sight. The structure subcomponents are at different formation stages. The clusters have a core dominated by passive galaxies and an established red sequence. The remaining structures are a mix of star-forming galaxy overdensities and forming groups. The presence of quiescent galaxies in the core of the latter shows that 'pre-processing' has already happened before the groups fall into theirmoremassive neighbours. Our spectroscopy allows us to derive spectral index measurements e.g. emission/absorption line equivalent widths, strength of the 4000Å break, valuable to investigate the star formation history of structure members. Based on these line measurements, we select a population of 'post-starburst' galaxies. These galaxies are preferentially found within the virial radius of clusters, supporting a scenario in which their recent quenching could be prompted by gas stripping by the dense intracluster medium. We derive stellar age estimates using Markov Chain Monte Carlo-based spectral fitting for quiescent galaxies and find a correlation between ages and colours/stellar masses which favours a top-down formation scenario of the red sequence. A catalogue of~650 redshifts in UDS is released alongside the paper (via MNRAS online data). [ABSTRACT FROM AUTHOR]

We present a large-scale galaxy structure Cl J021734-0513 at z ∼ 0.65 discovered in the UKIDSS UDS field, made of ∼20 galaxy groups and clusters, spreading over 10Mpc. We report on a VLT/VIMOS spectroscopic follow-up program that, combined with past spectroscopy, allowed us to confirm four galaxy clusters (M200 ∼ 1014 M☉) and a dozen associated groups and star-forming galaxy overdensities. Two additional filamentary structures at z∼0.62 and 0.69 and foreground and background clusters at 0.6 < ʑ < 0.7 were also confirmed along the line of sight. The structure subcomponents are at different formation stages. The clusters have a core dominated by passive galaxies and an established red sequence. The remaining structures are a mix of star-forming galaxy overdensities and forming groups. The presence of quiescent galaxies in the core of the latter shows that 'pre-processing' has already happened before the groups fall into theirmoremassive neighbours. Our spectroscopy allows us to derive spectral index measurements e.g. emission/absorption line equivalent widths, strength of the 4000Å break, valuable to investigate the star formation history of structure members. Based on these line measurements, we select a population of 'post-starburst' galaxies. These galaxies are preferentially found within the virial radius of clusters, supporting a scenario in which their recent quenching could be prompted by gas stripping by the dense intracluster medium. We derive stellar age estimates using Markov Chain Monte Carlo-based spectral fitting for quiescent galaxies and find a correlation between ages and colours/stellar masses which favours a top-down formation scenario of the red sequence. A catalogue of ∼650 redshifts in UDS is released alongside the paper (via MNRAS online data). [ABSTRACT FROM AUTHOR]

We present the evolution in the number density and stellar mass functions of photometrically selected post-starburst galaxies in the UKIDSS Ultra Deep Survey, with redshifts of 0.5 < z < 2 and stellar masses log (M/M⊙) >10. We find that this transitionary species of galaxy is rare at all redshifts, contributing  ~5 per cent of the total population at z ~ 2, to <1 per cent by z ~ 0.5. By comparing the mass functions of quiescent galaxies to post-starburst galaxies at three cosmic epochs, we show that rapid quenching of star formation can account for 100 per cent of quiescent galaxy formation, if the post-starburst spectral features are visible for ~250 Myr. The flattening of the low-mass end of the quiescent galaxy stellar mass function seen at z ~ 1 can be entirely explained by the addition of rapidly quenched galaxies. Only if a significant fraction of post-starburst galaxies have features that are visible for longer than 250 Myr, or they acquire new gas and return to the star-forming sequence, can there be significant growth of the red sequence from a slower quenching route. The shape of the mass function of these transitory post-starburst galaxies resembles that of quiescent galaxies at z ~ 2, with a preferred stellar mass of log (M/M⊙)  ~10.6, but evolves steadily to resemble that of star-forming galaxies at z < 1. This leads us to propose a dual origin for post-starburst galaxies: (1) at z ≳ 2 they are exclusively massive galaxies that have formed the bulk of their stars during a rapid assembly period, followed by complete quenching of further star formation; (2) at z ≲ 1 they are caused by the rapid quenching of gas-rich star-forming galaxies, independent of stellar mass, possibly due to environment and/or gas-rich major mergers. [ABSTRACT FROM AUTHOR]

Due to significant galaxy contamination and impurity in stellar mass selected samples (up to 95 per cent from z = 0-3), we examine the star formation history, quenching time-scales, and structural evolution of galaxies using a constant number density selection with data from the United Kingdom Infra-Red Deep Sky Survey Ultra-Deep Survey field. Using this methodology, we investigate the evolution of galaxies at a variety of number densities from z = 0-3. We find that samples chosen at number densities ranging from 3 × 10-4 to 10-5 galaxies Mpc-3 (corresponding to z ~ 0.5 stellar masses of M* = 1010.95-11.6 M0) have a star-forming blue fraction of ~50 per cent at z ~ 2.5, which evolves to a nearly 100 per cent quenched red and dead population by z ~ 1. We also see evidence for number density downsizing, such that the galaxies selected at the lowest densities (highest masses) become a homogeneous red population before those at higher number densities. Examining the evolution of the colours for these systems furthermore shows that the formation redshift of galaxies selected at these number densities is zform > 3. The structural evolution through size and Sérsic index fits reveal that while there remains evolution in terms of galaxies becoming larger and more concentrated in stellar mass at lower redshifts, the magnitude of the change is significantly smaller than for a mass-selected sample. We also find that changes in size and structure continues at z < 1, and is coupled strongly to passivity evolution. We conclude that galaxy structure is driving the quenching of galaxies, such that galaxies become concentrated before they become passive. [ABSTRACT FROM AUTHOR]

We combine photometry from the Ultra Deep Survey (UDS), Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) UDS and CANDELS the Great Observatories Origins Deep Survey-South (GOODS-S) surveys to construct the galaxy stellar mass function probing both the low- and high-mass end accurately in the redshift range 0.3 < z < 3. The advantages of using a homogeneous concatenation of these data sets include meaningful measures of environment in the UDS, due to its large area (0.88 deg²), and the high-resolution deep imaging in CANDELS (H160 > 26.0), affording us robust measures of structural parameters. We construct stellar mass functions for the entire sample as parametrized by the Schechter function, and find that there is a decline in the values of ɸ and of α with higher redshifts, and a nearly constant M* up to z ~ 3. We divide the galaxy stellar mass function by colour, structure, and environment and explore the links between environmental overdensity, morphology, and the quenching of star formation. We find that a double Schechter function describes galaxies with high Sérsic index (n > 2.5), similar to galaxies which are red or passive. The low-mass end of the n > 2.5 stellar mass function is dominated by blue galaxies, whereas the high-mass end is dominated by red galaxies. This shows that there is a possible link between morphological evolution and star formation quenching in high mass galaxies, which is not seen in lower mass systems. This in turn suggests that there are strong mass-dependent quenching mechanisms. In addition, we find that the number density of high-mass systems is elevated in dense environments, suggesting that an environmental process is building up massive galaxies quicker in over densities than in lower densities. [ABSTRACT FROM AUTHOR]

The formation of bars in disc galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in discs decreases from the local Universe to z ∼ 1, and by z > 1 simulations predict that bar features in dynamically mature discs should be extremely rare. Here, we report the discovery of strong barred structures in massive disc galaxies at z ∼ 1.5 in deep rest-frame optical images from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. From within a sample of 876 disc galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a subsample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5 ≤ z ≤ 2 ( $f_{{\rm bar}} = 10.7^{+6.3}_{-3.5}$ per cent after correcting for incompleteness) does not significantly evolve. We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disc galaxies have evolved over the last 11 billion years. [ABSTRACT FROM AUTHOR]

We present a study on the stellar mass growth of the progenitors of local massive galaxies with a variety of number density selections with n ≤ 1 × 10−4 Mpc−3 (corresponding to M* = 1011.24 M⊙ at z = 0.3) in the redshift range 0.3 < z < 3.0. We select the progenitors of massive galaxies using a constant number density selection, and one which is adjusted to account for major mergers. We find that the progenitors of massive galaxies grow by a factor of 4 in total stellar mass over this redshift range. On average the stellar mass added via the processes of star formation, major and minor mergers account for 24 ± 8, 17 ± 15 and 34 ± 14 per cent, respectively, of the total galaxy stellar mass at z = 0.3. Therefore 51 ± 20 per cent of the total stellar mass in massive galaxies at z = 0.3 is created externally to their z = 3 progenitors. We explore the implication of these results on the cold gas accretion rate and size evolution of the progenitors of most massive galaxies over the same redshift range. We find an average gas accretion rate of ∼66 ± 32 M⊙ yr−1 over the redshift range of 1.5 < z < 3.0. We find that the size evolution of a galaxy sample selected this way is on average lower than the findings of other investigations. [ABSTRACT FROM AUTHOR]

ABSTRACT We present spectroscopic and 11-band photometric redshifts for galaxies in the 100- μJy Subaru/ XMM-Newton Deep Field radio source sample. We find good agreement between our redshift distribution and that predicted by the Square Kilometre Array (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 ∼1 mJy 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 active galactic nuclei below the break in the RLF 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. [ABSTRACT FROM AUTHOR]

ABSTRACT To investigate the evolution in the relation between galaxy stellar and central black hole mass, we identify a population of 508 X-ray-selected active galactic nuclei (AGN) at 0.4 < z < 6 residing within host galaxies with stellar masses in the range 1010 M⊙ < M* < 1012 M⊙. From this sample we construct a volume-limited complete sample of 85 AGN with host galaxy stellar masses M* > 1010.5 M⊙, and specific X-ray luminosities LX > 2.35 × 1043 erg s−1 at 0.4 < z < 3. We calculate the Eddington limiting masses of the supermassive black holes (SMBHs) residing at the centre of these galaxies, and observe an increase in the average Eddington limiting black hole mass with redshift. While the black hole mass and Eddington ratio, μ, are degenerate, if we assume that the local MBH - M* relation holds at all redshifts we find that the mean Eddington ratio μ rises from 0.056 ± 0.010 at z= 0.7 to 0.087 ± 0.011 at z= 1.25, with no significant evolution thereafter to z= 3. Alternatively, by assuming that there is no evolution in μ and then that there is maximum possible evolution to the Eddington limit, we quantify the maximum possible evolution in the M*/ MBH ratio as lying in the range 700 < M*/ MBH < 10 000, compared with the local value of M*/ MBH∼ 1000. We furthermore find that the fraction of galaxies which are AGN (with LX > 2.35 × 1043 erg s−1) rises with redshift from 1.2 ± 0.2 per cent at z= 0.7 to 7.4 ± 2.0 per cent at z= 2.5. We use our results to calculate the maximum time-scales for which our sample of AGN can continue to accrete at their observed rates before surpassing the local galaxy-black hole mass relation. We use these time-scales to calculate the total fraction of massive galaxies which will be active (with LX > 2.35 × 1043 erg s−1) since z= 3, finding that at least ∼40 per cent of all massive galaxies will be Seyfert luminosity AGN or brighter during this epoch. Further, we calculate the energy density due to AGN activity in the Universe as 1.0 (±0.3) × 1057 erg Mpc−3 Gyr−1, potentially providing a significant source of energy for AGN feedback on star formation. We also use this method to compute the evolution in the X-ray luminosity density of AGN with redshift, finding that massive galaxy Seyfert luminosity AGN are the dominant source of X-ray emission in the Universe at z < 3. [ABSTRACT FROM AUTHOR]

We construct a sample of extremely red objects (EROs) within the UKIDSS Ultra Deep Survey by combining the Early Data Release with optical data from the Subaru/ XMM–Newton Deep Field. We find a total of 3715 objects over 2013 arcmin2 with and , which is a higher surface density than found by previous studies. This is partly due to our ability to use a small aperture in which to measure colours, but is also the result of a genuine overdensity of objects compared to other fields. We separate our sample into passively evolving and dusty star-forming galaxies using their RJK colours and investigate their radio properties using a deep radio map. The dusty population has a higher fraction of individually detected radio sources and a higher mean radio flux density among the undetected objects, but the passive population has a higher fraction of bright radio sources, suggesting that active galactic nuclei are more prevalent among the passive ERO population. [ABSTRACT FROM AUTHOR]