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We present a set of photometric catalogs primarily aimed at providing the community with a comprehensive database for the study of galaxy populations in the high redshift Universe. The set gathers data from eight JWST NIRCam observational programs, targeting the Abell 2744 (GLASS-JWST, UNCOVER, DDT2756 and GO3990), EGS (CEERS), COSMOS and UDS (PRIMER), and GOODS North and South (JADES and NGDEEP) deep fields, for a total area of $\sim$0.2 sq. degrees. Photometric estimates are obtained by means of well-established techniques, including tailored improvements designed to enhance the performance on the specific dataset. We also include new measurements from HST archival data, thus collecting 16 bands spanning from 0.44 to 4.44 $\mu$m. A grand total of $\sim$530 thousand sources is detected on stacks of NIRCam 3.56 and 4.44 $\mu$m mosaics. We assess the photometric accuracy by comparing fluxes and colors against archival catalogs. We also provide photometric redshift estimates, statistically validated against a large set of robust spectroscopic data. The catalogs are publicly available on the Astrodeep website., Comment: 28 pages, 16 figures; accepted for publication on Astronomy & Astrophysics

Two groundbreaking new facilities will commence operations early in the 2020s and thereafter define much of the broad landscape of US optical-infrared astronomy in the remaining decade. The Large Synoptic Survey Telescope (LSST), perched atop Cerro Pachon in the Chilean Andes, will revolutionize the young field of Time Domain Astronomy through its wide-field, multi-band optical imaging survey. At the same time, the James Webb Space Telescope (JWST), orbiting at the Sun-Earth L2 Lagrange point, will provide stunningly high-resolution views of selected targets from the red end of the optical spectrum to the mid-infrared. However, the spatial resolution of the LSST observations will be limited by atmospheric seeing, while JWST will be limited in its time-domain capabilities. This paper highlights the scientific opportunities lying between these two landmark missions, i.e., science enabled by systems capable of astronomical observations with both high cadence in the time domain and high resolution in the spatial domain. The opportunities range from constraining the late phases of stellar evolution in nearby resolved populations to constraining dark matter distributions and cosmology using lensed transient sources. We describe a system that can deliver the required capabilities., Comment: Science white paper submitted to Astro2020

VANDELS is a uniquely-deep spectroscopic survey of high-redshift galaxies with the VIMOS spectrograph on ESO's Very Large Telescope (VLT). The survey has obtained ultra-deep optical (0.48 < lambda < 1.0 micron) spectroscopy of ~2100 galaxies within the redshift interval 1.0 < z < 7.0, over a total area of ~0.2 sq. degrees centred on the CANDELS UDS and CDFS fields. Based on accurate photometric redshift pre-selection, 85% of the galaxies targeted by VANDELS were selected to be at z>=3. Exploiting the red sensitivity of the refurbished VIMOS spectrograph, the fundamental aim of the survey is to provide the high signal-to-noise ratio spectra necessary to measure key physical properties such as stellar population ages, masses, metallicities and outflow velocities from detailed absorption-line studies. Using integration times calculated to produce an approximately constant signal-to-noise ratio (20 < t_int < 80 hours), the VANDELS survey targeted: a) bright star-forming galaxies at 2.4 < z < 5.5, b) massive quiescent galaxies at 1.0 < z < 2.5, c) fainter star-forming galaxies at 3.0 < z < 7.0 and d) X-ray/Spitzer-selected active galactic nuclei and Herschel-detected galaxies. By targeting two extragalactic survey fields with superb multi-wavelength imaging data, VANDELS will produce a unique legacy data set for exploring the physics underpinning high-redshift galaxy evolution. In this paper we provide an overview of the VANDELS survey designed to support the science exploitation of the first ESO public data release, focusing on the scientific motivation, survey design and target selection., Comment: 19 pages, 9 figures, accepted for publication in MNRAS

The Frontier Fields are a director's discretionary time campaign with HST and the Spitzer Space Telescope to see deeper into the universe than ever before. The Frontier Fields combine the power of HST and Spitzer with the natural gravitational telescopes of massive high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies ever obtained. Six clusters - Abell 2744, MACSJ0416.1-2403, MACSJ0717.5+3745, MACSJ1149.5+2223, Abell S1063, and Abell 370 - were selected based on their lensing strength, sky darkness, Galactic extinction, parallel field suitability, accessibility to ground-based facilities, HST, Spitzer and JWST observability, and pre-existing ancillary data. These clusters have been targeted by the HST ACS/WFC and WFC3/IR with coordinated parallels of adjacent blank fields for over 840 HST orbits. The Spitzer Space Telescope has dedicated > 1000 hours of director's discretionary time to obtain IRAC 3.6 and 4.5 micron imaging to ~26.5, 26.0 ABmag 5-sigma point-source depths in the six cluster and six parallel Frontier Fields. The Frontier Field parallel fields are the second-deepest observations thus far by HST with ~29th ABmag 5-sigma point source depths in seven optical - near-infrared bandpasses. Galaxies behind the Frontier Field cluster lenses experience typical magnification factors of a few, with small regions near the critical curves magnified by factors 10-100. Therefore, the Frontier Field cluster HST images achieve intrinsic depths of ~30-33 magnitudes over very small volumes. Early studies of the Frontier Fields have probed galaxies fainter than any seen before during the epoch of reionization 6 < z < 10, mapped out the cluster dark matter to unprecedented resolution, and followed lensed transient events., Comment: submitted to ApJ; 18 pages; see http://www.stsci.edu/hst/campaigns/frontier-fields/ and http://ssc.spitzer.caltech.edu/warmmission/scheduling/approvedprograms/ddt/frontier/ for data and more information

We report a new analysis of the Hubble Frontier Fields clusters Abell 2744 and MACS 0416 using wavelet decomposition to remove the cluster light, enabling the detection of highly magnified (>50x) galaxies a factor of 10x fainter in luminosity than previous studies. We find 167 galaxies at z > 6, and with this sample we are able to characterize the UV luminosity function to M_UV = -12.5 at z ~ 6, -14 at z ~ 7 and -15 at z ~ 8. We find a steep faint-end slope (alpha <-2), and with our improved statistics at the faint end we reduce the fractional uncertainty on alpha to <2% at z ~ 6 - 7 and 4% at z ~ 8. We also investigate the systematic uncertainty due to the lens modelling by using every available lens model individually and comparing the results; this systematic fractional uncertainty on alpha is <4% at all redshifts. We now directly observe galaxies in the luminosity regime where simulations predict a change in the faint-end slope of the luminosity function, yet our results provide statistically very strong evidence against any turnover in the luminosity range probed, more consistent with simulations in which stars form in lower-mass halos. Thus we find strong support for the extension of the steep luminosity function to M_UV = -13 at z > 6, consistent with the number of faint galaxies needed to reionize the Universe under standard assumptions., Comment: 28 pages, 13 figures, published in ApJ

Galaxies with stellar masses near M* contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present day stellar masses near M*, at 5x10^10 Msol (MW-mass) and 10^11 Msol (M31-mass). We study the typical progenitors of these galaxies using ZFOURGE, a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galaxies out to z~3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far-IR luminosities, and star-formation rates combining our deep multiwavelength imaging with near-IR HST imaging from CANDELS, and far-IR imaging from GOODS-H and CANDELS-H. The typical MW-mass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages, to redder dust-obscured IR-luminous galaxies in intermediate stages, and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of 2-3 lower than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star-formation in present-day M* galaxies requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and star-formation rates imply that the baryonic cold-gas fractions drop as galaxies evolve from high redshift to z~0 and are strongly anticorrelated with an increase in the S\'ersic index. Therefore, the growth of galaxy bulges in M* galaxies corresponds to a rapid decline in the galaxy gas fractions and/or a decrease in the star-formation efficiency., Comment: Accepted for publication in ApJ; 25 pages, emulateapj format

We study the relationship between the structure and star-formation rate (SFR) of X-ray selected low and moderate luminosity active galactic nuclei (AGNs) in the two Chandra Deep Fields, using Hubble Space Telescope imaging from the Cosmic Assembly Near Infrared Extragalactic Legacy Survey (CANDELS) and deep far-infrared maps from the PEP+GOODS-Herschel survey. We derive detailed distributions of structural parameters and FIR luminosities from carefully constructed control samples of galaxies, which we then compare to those of the AGNs. At z~1, AGNs show slightly diskier light profiles than massive inactive (non-AGN) galaxies, as well as modestly higher levels of gross galaxy disturbance (as measured by visual signatures of interactions and clumpy structure). In contrast, at z~2, AGNs show similar levels of galaxy disturbance as inactive galaxies, but display a red central light enhancement, which may arise due to a more pronounced bulge in AGN hosts or due to extinguished nuclear light. We undertake a number of tests of these alternatives, but our results do not strongly favour one interpretation over the other. The mean SFR and its distribution among AGNs and inactive galaxies are similar at z>1.5. At z<1, however, clear and significant enhancements are seen in the SFRs of AGNs with bulge-dominated light profiles. These trends suggest an evolution in the relation between nuclear activity and host properties with redshift, towards a minor role for mergers and interactions at z>1.5., Comment: 25 pages (double-column), 17 Figures, under review at A&A

Chandra data in the COSMOS, AEGIS-XD and 4Ms CDFS are combined with optical/near-IR photometry to determine the rest-frame U-V vs V-J colours of X-ray AGN hosts at mean redshifts 0.40 and 0.85. This combination of colours (UVJ) provides an efficient means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasises differences between AGN split by their UVJ colours. AGN in quiescent galaxies are dominated by spheroids, while star-forming hosts are split between bulges and disks. The UVJ diagram of AGN hosts is then used to set limits on the accretion density associated with evolved and star-forming systems. Most of the black hole growth since z~1 is associated with star-forming hosts. Nevertheless, ~15-20% of the X-ray luminosity density since z~1, is taking place in the quiescent region of the UVJ diagram. For the z~0.40 subsample, there is tentative evidence (2sigma significance), that AGN split by their UVJ colours differ in Eddington ratio. AGN in star-forming hosts dominate at high Eddington ratios, while AGN in quiescent hosts become increasingly important as a fraction of the total population toward low Eddington ratios. At higher redshift, z~0.8, such differences are significant at the 2sigma level only at Eddington ratios >1e-3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of SMBHs at the centres of galaxies. We compare our results with the GALFORM semi-analytic model, which postulates two black hole fuelling modes, the first linked to star-formation and the second occuring in passive galaxies. GALFORM predicts a larger fraction of black hole growth in quiescent galaxies at z<1, compared to the data. Relaxing the strong assumption of the model that passive AGN hosts have zero star-formation rate could reconcile this disagreement., Comment: MNRAS accepted

Testing theories of hierarchical structure formation requires estimating the distribution of galaxy morphologies and its change with redshift. One aspect of this investigation involves identifying galaxies with disturbed morphologies (e.g., merging galaxies). This is often done by summarizing galaxy images using, e.g., the CAS and Gini-M20 statistics of Conselice (2003) and Lotz et al. (2004), respectively, and associating particular statistic values with disturbance. We introduce three statistics that enhance detection of disturbed morphologies at high-redshift (z ~ 2): the multi-mode (M), intensity (I), and deviation (D) statistics. We show their effectiveness by training a machine-learning classifier, random forest, using 1,639 galaxies observed in the H band by the Hubble Space Telescope WFC3, galaxies that had been previously classified by eye by the CANDELS collaboration (Grogin et al. 2011, Koekemoer et al. 2011). We find that the MID statistics (and the A statistic of Conselice 2003) are the most useful for identifying disturbed morphologies. We also explore whether human annotators are useful for identifying disturbed morphologies. We demonstrate that they show limited ability to detect disturbance at high redshift, and that increasing their number beyond approximately 10 does not provably yield better classification performance. We propose a simulation-based model-fitting algorithm that mitigates these issues by bypassing annotation., Comment: 15 pages, 14 figures, accepted for publication in MNRAS

We present a study of the prevalence, strength, and kinematics of ultraviolet FeII and MgII emission lines in 212 star-forming galaxies at z = 1 selected from the DEEP2 survey. We find FeII* emission in composite spectra assembled on the basis of different galaxy properties, indicating that FeII* emission is prevalent at z = 1. In these composites, FeII* emission is observed at roughly the systemic velocity. At z = 1, we find that the strength of FeII* emission is most strongly modulated by dust attenuation, and is additionally correlated with redshift, star-formation rate, and [OII] equivalent width, such that systems at higher redshifts with lower dust levels, lower star-formation rates, and larger [OII] equivalent widths show stronger FeII* emission. We detect MgII emission in at least 15% of the individual spectra and we find that objects showing stronger MgII emission have higher specific star-formation rates, smaller [OII] linewidths, larger [OII] equivalent widths, lower dust attenuations, and lower stellar masses than the sample as a whole. MgII emission strength exhibits the strongest correlation with specific star-formation rate, although we find evidence that dust attenuation and stellar mass also play roles in the regulation of MgII emission. Future integral field unit observations of the spatial extent of FeII* and MgII emission in galaxies with high specific star-formation rates, low dust attenuations, and low stellar masses will be important for probing the morphology of circumgalactic gas., Comment: 29 pages, 22 figures, 2 tables; accepted to ApJ

We have used high-resolution, HST WFC3/IR, near-infrared imaging to conduct a detailed bulge-disk decomposition of the morphologies of ~200 of the most massive (M_star > 10^11 M_solar) galaxies at 12 they are mostly disk-dominated. Interestingly, we find that while most of the quiescent galaxies are bulge-dominated, a significant fraction (25-40%) of the most quiescent galaxies, have disk-dominated morphologies. Thus, our results suggest that the physical mechanisms which quench star-formation activity are not simply connected to those responsible for the morphological transformation of massive galaxies., Comment: Contributed article (4 pages, 2 figures), IAU Symposium 295 on "The intriguing life of massive galaxies", to appear in the proceedings of the IAU XXVIII General Assembly, Beijing, 2012, (Eds: Daniel Thomas, Anna Pasquali, Ignacio Ferreras)

We have used deep, HST, near-IR imaging to study the morphological properties of the most massive galaxies at high z, modelling the WFC3/IR H-band images of the ~200 galaxies in the CANDELS-UDS field with 1 < z_phot < 3, and stellar masses M_star > 10^11 M_sun. We have used both single-Sersic and bulge+disk models, have investigated the errors/biases introduced by uncertainties in the background and the PSF, and have obtained formally-acceptable model fits to >90% of the galaxies. Our results indicate that these massive galaxies at 1 < z < 3 lie both on and below the local size-mass relation, with a median R_e~2.6 kpc, a factor of ~2.3 smaller than comparably-massive local galaxies. Moreover, we find that bulge-dominated objects in particular show evidence for a growing bimodality in the size-mass relation with increasing z, and by z > 2 the compact bulges display effective radii a factor ~4 smaller than local ellipticals of comparable mass. These trends appear to extend to the bulge components of disk-dominated galaxies, and vice versa. We also find that, while such massive galaxies at low z are bulge-dominated, at 1 < z < 2 they are predominantly mixed bulge+disk systems, and by z > 2 they are mostly disk-dominated. The majority of the disk-dominated galaxies are actively forming stars, but this is also true for many of the bulge-dominated systems. Interestingly, however, while most of the quiescent galaxies are bulge-dominated, we find that a significant fraction (25-40%) of the most quiescent galaxies have disk-dominated morphologies. Thus, while our results show that the massive galaxy population is undergoing dramatic changes at this crucial epoch, they also suggest that the physical mechanisms which quench star-formation activity are not simply connected to those responsible for the morphological transformation of massive galaxies into present-day giant ellipticals., Comment: 39 pages, 19 figures, 2 tables, submitted to MNRAS

We investigate galactic-scale outflowing winds in 72 star-forming galaxies at z~1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering SiII, CIV, FeII, MgII, and MgI lines in the rest-frame ultraviolet. Using GALEX, HST, and Spitzer imaging, we examine galaxies on a per-object basis in order to understand both the prevalence of galactic winds at z~1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from the centroids of FeII interstellar absorption lines, span the interval [-217, +155] km/s. We find that ~40% (10%) of the sample exhibits blueshifted FeII lines at the 1-sigma (3-sigma) level. We also measure maximal outflow velocities using the profiles of the FeII and MgII lines, and show that MgII frequently traces higher velocity gas than FeII. Quantitative morphological parameters derived from the HST imaging suggest that mergers are not a prerequisite for driving outflows. More face-on galaxies also show stronger winds than highly-inclined systems, consistent with the canonical picture of winds emanating perpendicular to galactic disks. Using star-formation rates calculated from GALEX data, and areas estimated from HST imaging, we detect a ~3-sigma correlation between outflow velocity and star-formation rate surface density, but only a weak (~1-sigma) trend between outflow velocity and star-formation rate. Higher resolution data are needed in order to test the scaling relations between outflow velocity and both star-formation rate and star-formation rate surface density predicted by theory., Comment: 34 pages, 25 figures, accepted for publication in ApJ

We present the Arizona CDFS Environment Survey (ACES), a recently-completed spectroscopic redshift survey of the Chandra Deep Field South (CDFS) conducted using IMACS on the Magellan-Baade telescope. In total, the survey targeted 7277 unique sources down to a limiting magnitude of R = 24.1, yielding 5080 secure redshifts across the ~30' x 30' extended CDFS region. The ACES dataset delivers a significant increase to both the spatial coverage and the sampling density of the spectroscopic observations in the field. Combined with previously-published, spectroscopic redshifts, ACES now creates a highly-complete survey of the galaxy population at R < 23, enabling the local galaxy density (or environment) on relatively small scales (~1 Mpc) to be measured at z < 1 in one of the most heavily-studied and data-rich fields in the sky. Here, we describe the motivation, design, and implementation of the survey and present a preliminary redshift and environment catalog. In addition, we utilize the ACES spectroscopic redshift catalog to assess the quality of photometric redshifts from both the COMBO-17 and MUSYC imaging surveys of the CDFS., Comment: resubmitted to MNRAS; 12 pages, 12 figures, and 3 tables; updated redshift catalog available at http://mur.ps.uci.edu/~cooper/ACES/

We present the recent merger history of massive galaxies in a spectroscopically-confirmed proto-cluster at z=1.62. Using HST WFC3 near-infrared imaging from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), we select cluster galaxies and z ~ 1.6 field galaxies with M_star >= 3 x 10^10 M_sun, and determine the frequency of double nuclei or close companions with projected separations less than 20 kpc co-moving and stellar mass ratios between 1:1 and roughly 10:1. We find that four out of five spectroscopically-confirmed massive proto-cluster galaxies have double nuclei, and 42 +13/-25 % of all M_star >= 3 x 10^10 M_sun cluster candidates are either in close pair systems or have double nuclei. In contrast, only 4.5 +/- 2.6% of the field galaxies are in close pair/double nuclei systems. The implied merger rate per massive galaxy in the proto-cluster is 3-10 times higher than the merger rate of massive field galaxies at z ~ 1.6, depending upon the assumed mass ratios. Close pairs in the cluster have minor merger stellar mass ratios (M_primary:M_satellite ~ 6:1), while the field pairs are typically major mergers with stellar mass ratios between 1:1 and 4:1. At least half of the cluster mergers are dissipationless, as indicated by their red colors and low 24 micron fluxes. Two of the double-nucleated cluster members have X-ray detected AGN with L_x > 10^43 erg/s, and are strong candidates for dual or offset super-massive black holes. We conclude that the massive z = 1.62 proto-cluster galaxies are undergoing accelerated assembly relative to the field population, and discuss the implications for galaxy evolution in proto-cluster environments., Comment: 9 paper, 6 color figure, 1 table; submitted to ApJ

We discuss the structural and morphological properties of galaxies in a z=1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (< 1kpc), massive galaxies compared to CANDELS field galaxies at z=1.6. As a result the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z~1.6 to the present, growing as (1+z)^(-0.6+/-0.1). If this result is generalizable, then it implies that physical processes associated with the denser cluster region seems to have caused accelerated size growth in quiescent galaxies prior to z=1.6 and slower subsequent growth at z<1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z=1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z<1 clusters., Comment: Accepted for publication in ApJ. 14 pages in emulateapj format. Replacement includes improvements from referee report, and updates and additions to references

We report on the evolution of the number density and size of early-type galaxies from z~2 to z~0. We select a sample of 563 massive (M>10^{10} Msun), passively evolving (SSFR<10^{-2} Gyr^{-1}) and morphologically spheroidal galaxies at 01.2 and z<1.2, respectively). We measure a significant evolution of the mass-size relation of early-type galaxies, with the fractional increment that is almost independent on the stellar mass. Early-type galaxies (ETGs) formed at z>1 appear to be preferentially small, and the evolution of the mass-size relation at z<1 is driven by both the continuous size growth of the compact galaxies and the appearance of new ETGs with large sizes. We also find that the number density of all passive early-type galaxies increases rapidly, by a factor of 5, from z~2 to z~1, and then more mildly by another factor of 1.5 from z~1 to z~0. We interpret these results as the evidence that the bulk of the ETGs are formed at 1

We describe the effect of AGN light on host galaxy optical and UV-optical colours, as determined from X-ray-selected AGN host galaxies at z~1, and compare the AGN host galaxy colours to those of a control sample matched to the AGN sample in both redshift and stellar mass. We identify as X-ray-selected AGNs 8.7 +4/-3 per cent of the red-sequence control galaxies, 9.8 +/-3 per cent of the blue-cloud control galaxies, and 14.7 +4/-3 per cent of the green-valley control galaxies. The nuclear colours of AGN hosts are generally bluer than their outer colours, while the control galaxies exhibit redder nuclei. AGNs in blue-cloud host galaxies experience less X-ray obscuration, while AGNs in red-sequence hosts have more, which is the reverse of what is expected from general considerations of the interstellar medium. Outer and integrated colours of AGN hosts generally agree with the control galaxies, regardless of X-ray obscuration, but the nuclear colours of unobscured AGNs are typically much bluer, especially for X-ray luminous objects. Visible point sources are seen in many of these, indicating that the nuclear colours have been contaminated by AGN light and that obscuration of the X-ray radiation and visible light are therefore highly correlated. Red AGN hosts are typically slightly bluer than red-sequence control galaxies, which suggests that their stellar populations are slightly younger. We compare these colour data to current models of AGN formation. The unexpected trend of less X-ray obscuration in blue-cloud galaxies and more in red-sequence galaxies is problematic for all AGN feedback models, in which gas and dust is thought to be removed as star formation shuts down. [See paper for full abstract.], Comment: Accepted to MNRAS. 19 pages, 14 figures, 1 table; table, four figures (4, 6, 11, 13) revised to reflect corrected values for one of our objects; results unchanged

We assess the effects of simulated active galactic nuclei (AGNs) on the colour and morphology measurements of their host galaxies. To test the morphology measurements, we select a sample of galaxies not known to host AGNs and add a series of point sources scaled to represent specified fractions of the observed V band light detected from the resulting systems; we then compare morphology measurements of the simulated systems to measurements of the original galaxies. AGN contributions >20 per cent bias most of the morphology measurements tested, though the extent of the apparent bias depends on the morphological characteristics of the original galaxies. We test colour measurements by adding to non-AGN galaxy spectra a quasar spectrum scaled to contribute specified fractions of the rest-frame B band light detected from the resulting systems. A quasar fraction of 5 per cent can move the NUV-r colour of an elliptical galaxy from the UV-optical red sequence to the green valley, and 20 per cent can move it into the blue cloud. Combining the colour and morphology results, we find that a galaxy/AGN system with an AGN contribution >20 per cent may appear bluer and more bulge-dominated than the underlying galaxy. We conclude that (1) bulge-dominated, E/S0/Sa, and early-type morphology classifications are accurate for red AGN host galaxies and may be accurate for blue host galaxies, unless the AGN manifests itself as a well-defined point source; and (2) although highly unobscured AGNs, such as the quasar used for our experiments, can significantly bias the measured colours of AGN host galaxies, it is possible to identify such systems by examining optical images of the hosts for the presence of a point source and/or measuring the level of nuclear obscuration., Comment: 18 pages, 19 figures, 1 table. Accepted for publication in MNRAS

We present near-IR images, obtained with the Hubble Space Telescope (HST) and the WFC3/IR camera, of six passive and massive galaxies at redshift 1.3

We use morphological information of X-ray selected AGN hosts to set limits on the fraction of the accretion density of the Universe at z~1 that is not likely to be associated with major mergers. Deep X-ray observations are combined with high resolution optical data from the Hubble Space Telescope in the AEGIS, GOODS North and GOODS South fields to explore the morphological breakdown of X-ray sources in the redshift interval 0.51e44 erg/s) compared to predictions for the stochastic fueling of massive black holes in disk galaxies., Comment: Accepted for publication in MNRAS

We explore the role of AGN in establishing and/or maintaining the bimodal colour distribution of galaxies by quenching their star-formation and hence, causing their transition from the blue to the red cloud. Important tests for this scenario include (i) the X-ray properties of galaxies in the transition zone between the two clouds and (ii) the incidence of AGN in post-starbursts, i.e. systems observed shortly after (<1Gyr) the termination of their star-formation. We perform these tests by combining deep Chandra observations with multiwavelength data from the AEGIS survey. Stacking the X-ray photons at the positions of galaxies (0.4

We analyze star formation (SF) as a function of stellar mass (M_*) and redshift z in the All Wavelength Extended Groth Strip International Survey (AEGIS), for star-forming field galaxies with M_* >~ 10^10 M_sun out to z=1.1. The data indicate that the high specific SF rates (SFR) of many less massive galaxies do not represent late, irregular or recurrent, starbursts in evolved galaxies. They rather seem to reflect the onset (initial burst) of the dominant SF episode of galaxies, after which SF gradually declines on Gyr timescales to z=0 and forms the bulk of a galaxy's M_*. With decreasing mass, this onset of major SF shifts to decreasing z for an increasing fraction of galaxies (staged galaxy formation). This process may be an important component of the ``downsizing'' phenomenon. We find that the predominantly gradual decline of SFR (Noeske et al. 2007, this volume) can be reproduced by exponential SF histories (tau models), if less massive galaxies have systematically longer e-folding times tau, and a later onset of SF (z_f). Our model can provide a first parametrization of SFR as a function of M_* and z, and quantify mass-dependences of tau and z_f, from direct observations of M_* and SFR up to z>1. The observed evolution of SF in galaxies can plausibly reflect the dominance of gradual gas exhaustion. The data are also consistent with the history of cosmological accretion onto Dark Matter halos., Comment: 5 pages, 2 figures, emulateapj; ApJ Letters, accepted; AEGIS special issue; proof-level corrections added; removed former footnote 10 (erroneous)

We analyze star formation (SF) as a function of stellar mass (M*) and redshift z in the All Wavelength Extended Groth Strip International Survey (AEGIS). For 2905 field galaxies, complete to 10^10(10^10.8) Msun at z<0.7(1), with Keck spectroscopic redshifts out to z=1.1, we compile SF rates (SFR) from emission lines, GALEX, and Spitzer MIPS 24 micron photometry, optical-NIR M* measurements, and HST morphologies. Galaxies with reliable signs of SF form a distinct "main sequence (MS)", with a limited range of SFR at a given M* and z (1 sigma < +-0.3 dex), and log(SFR) approximately proportional to log(M*). The range of log(SFR) remains constant to z>1, while the MS as a whole moves to higher SFR as z increases. The range of SFR along the MS constrains the amplitude of episodic variations of SF, and the effect of mergers on SFR. Typical galaxies spend ~67(95)% of their lifetime since z=1 within a factor of <~ 2(4) of their average SFR at a given M* and z. The dominant mode of the evolution of SF since z~1 is apparently a gradual decline of the average SFR in most individual galaxies, not a decreasing frequency of starburst episodes, or a decreasing factor by which SFR are enhanced in starbursts. LIRGs at z~1 seem to mostly reflect the high SFR typical for massive galaxies at that epoch. The smooth MS may reflect that the same set of few physical processes governs star formation prior to additional quenching processes. A gradual process like gas exhaustion may play a dominant role., Comment: 5 pages, 1 figure, emulateapj; ApJ Letters, accepted; AEGIS special issue; proof-level corrections added; title changed

As part of the "All Wavelength Extended Groth Strip International Survey" (AEGIS), we describe the panchromatic characterization of an X-ray luminous active galactic nucleus (AGN) in a merging galaxy at z=1.15. This object is detected at infrared (8mic, 24mic, 70mic, 160mic), submillimeter (850mic) and radio wavelengths, from which we derive a bolometric luminosity L_bol ~ 9x10^12 Lsol. We find that the AGN clearly dominates the hot dust emission below 40mic but its total energetic power inferred from the hard X-rays is substantially less than the bolometric output of the system. About 50% of the infrared luminosity is indeed produced by a cold dust component that probably originates from enshrouded star formation in the host galaxy. In the context of a coeval growth of stellar bulges and massive black holes, this source might represent a ``transition'' object sharing properties with both quasars and luminous starbursts. Study of such composite galaxies will help address how the star formation and disk-accretion phenomena may have regulated each other at high redshift and how this coordination may have participated to the build-up of the relationship observed locally between the masses of black holes and stellar spheroids., Comment: Accepted for publication in ApJL (AEGIS Special Edition) - 5 pages, 1 table, 3 figures

The All-wavelength Extended Groth Strip International Survey (AEGIS) team presents broad-band spectral energy distributions (SEDs), from X-ray to radio wavelengths, for 71 galaxies spanning the redshift range 0.55-1.16 (~0.7). Galaxies with secure redshifts were selected from a small (22 arcminute-square) sub-section of the Keck/DEIMOS galaxy redshift survey in the Extended Groth Strip field that has also been targeted for deep panchromatic imaging by Chandra (X-ray), GALEX (ultraviolet), Canada-France-Hawaii Telescope (optical), Hubble Space Telescope (optical/near infrared), Palomar Observatory (near infrared), Spitzer (mid/far infrared), and the Very Large Array (radio.) The absolute magnitude of the typical galaxy in our sample is M_B=-19.82. The ultraviolet to mid-infrared portion of their spectral energy distributions (SEDs) are found to be bracketed by two stellar-only model SEDs: an early burst followed by passive evolution and a constant star-formation rate since early times; this suggests that few of these galaxies are undergoing major starbursts. Approximately half the galaxies show a mid- to far-infrared excess relative to the model SEDs, consistent with thermal emission from interstellar dust. Two objects have power-law SEDs, indicating that they are dominated by active galactic nuclei; both are detected in X-rays. The galaxies are grouped by rest-frame color,quantitative optical morphology, and [OII] emission line strength (possible indicator of star formation). On average, the panchromatic SEDs of the galaxies, from the ultraviolet to the infrared, follow expected trends: redder SEDs are associated with red U-B, early-type morphology, and low [OII] emission, and vice versa for blue SEDs., Comment: 7 page, 3 figures, submitted to ApJL. Version with high-resolution images: http://aegis.ucolick.org/papers/konidaris.seds.2006.pdf. Author list fixed

We visually and quantitatively determine the host galaxy morphologies of 94 intermediate redshift (0.2 < z < 1.2) active galactic nuclei (AGN), selected using Chandra X-ray and Spitzer mid-infrared data in the Extended Groth Strip. Using recently developed morphology measures, the second-order moment of the brightest 20% of a galaxy's flux (M_{20}) and the Gini coefficient, we find that X-ray-selected AGN mostly reside in E/S0/Sa galaxies (53^{+11}_{-10}%), while IR-selected AGN show no clear preference for host morphology. X-ray-selected AGN hosts are members of close pairs more often than the field population by a factor of 3.3+/-1.4, but most of these pair members appear to be undisturbed early-type galaxies and do not tend to show direct evidence of gravitational perturbations or interactions. Thus, the activation mechanism for AGN activity remains unknown, even for pair members., Comment: 11 pages, 2 figures, 1 table, accepted for publication in ApJL

We report on the results of a visual search for galaxy-scale strong gravitational lenses over 650 arcmin^2 of HST/ACS imaging in the DEEP2-EGS field. In addition to a previously-known Einstein Cross (the "Cross," HST J141735+52264, with z_lens=0.8106 and a published z_source=3.40), we identify two new strong galaxy-galaxy lenses with multiple extended arcs. The first, HST J141820+52361 (the ``Dewdrop''; z_lens=0.5798, lenses two distinct extended sources into two pairs of arcs z_source=0.while), 9818 the second, HST J141833+52435 (the ``Anchor''; z_lens=0.4625), produces a single pair of arcs (source redshift not yet known). All three definite lenses are fit well by simple singular isothermal ellipsoid models including external shear. Using the three-dimensional line-of-sight (LOS) information on galaxies from the DEEP2 data, we calculate the convergence and shear contributions, assuming singular isothermal sphere halos truncated at 200 h^-1 kpc. These are also compared against three-dimensional local-density estimates. We find that even strong lenses in demonstrably underdense local environments may be considerably affected by LOS contributions, which in turn, may be underestimates of the effect of large scale structure., Comment: ApJ Letters, submitted. Part of the AEGIS ApJL Special Issue. 4 Figures, 1 Table. For a version with full-resolution figures, please see http://www.slac.stanford.edu/~pjm/HAGGLeS/astroph/legs.pdf

We present the quantitative rest-frame B morphological evolution and galaxy merger fractions at 0.2 < z < 1.2 as observed by the All-wavelength Extended Groth Strip International Survey (AEGIS). We use the Gini coefficent and M_20 to identify major mergers and classify galaxy morphology for a volume-limited sample of 3009 galaxies brighter than 0.4 L_B^*, assuming pure luminosity evolution of 1.3 M_B per unit redshift. We find that the merger fraction remains roughly constant at 10 +/- 2% for 0.2 < z < 1.2. The fraction of E/S0/Sa increases from 21+/- 3% at z ~ 1.1 to 44 +/- 9% at z ~ 0.3, while the fraction of Sb-Ir decreases from 64 +/- 6% at z ~ 1.1 to 47 +/- 9% at z ~ 0.3. The majority of z < 1.2 Spitzer MIPS 24 micron sources with L(IR) > 10^11 L_sun are disk galaxies, and only ~ 15% are classified as major merger candidates. Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence at z ~ 1.1, while E/S0/Sa makeup over 90% of the red sequence at z ~ 0.3. Approximately 2% of our full sample are red mergers. We conclude (1) the galaxy merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star-formation rate density since z ~ 1 is a result of declining star-formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ~ 1.2., Comment: 24 pages, including 3 tables and 18 color figures; accepted to the Astrophysical Journal; high resolution version available at http://www.noao.edu/noao/staff/lotz/lotz_mergers.pdf

We apply a new approach to quantifying galaxy morphology and identifying galaxy mergers to the rest-frame far-ultraviolet images of 82 z ~ 4 Lyman break galaxies (LBGs) and 55 1.2 < z < 1.8 emission-line galaxies in the GOODS and Ultra Deep Fields. We compare the distributions of the Gini coefficient (G), second-order moment of the brightest 20% of galaxy light (M20), and concentration (C) for high-redshift and low-redshift galaxies with average signal to noise per pixel > 2.5 and Petrosian radii > 0.3 arcsec. Ten of the 82 LBGs have M20 >= -1.1 and possess bright double or multiple nuclei, implying a major-merger fraction of star-forming galaxies ~ 10-25% at M_{FUV} < -20, depending on our incompleteness corrections. Galaxies with bulge-like morphologies (G >= 0.55, M20 < -1.6) make up ~ 30% of the z ~ 4 LBG sample, while the remaining ~ 50% have G and M20 values higher than expected for smooth bulges and disks and may be star-forming disks, minor-mergers or post-mergers. The star-forming z ~ 1.5 galaxy sample has a morphological distribution which is similar to the UDF z ~ 4 LBGs, with an identical fraction of major-merger candidates but fewer spheroids. The observed morphological distributions are roughly consistent with current hierarchical model predictions for the major-merger rates and minor-merger induced starbursts at z ~ 1.5 and ~4. We also examine the rest-frame FUV-NUV and FUV-B colors as a function of morphology and find no strong correlations at either epoch., Comment: accepted by the Astrophysical Journal; 19 pages, including 13 figures and 1 table

We present the results of a deep narrow-band [OII] 3727 \AA emission-line search for faint ($g <$ 27), star-forming galaxies in the field of the $z=0.37$ MS1512.4+3647 cluster. We find no evidence for an over-density of emission-line sources relative to the field at $z \sim$ 0.4 (Hogg et al. 1998), and therefore conclude that the MS1512.4+3647 sample is dominated by field [OII] emission-line galaxies which lie along the $\sim$ 180 Mpc line of sight immediately in front and behind the cluster. This is surprising, given that the previously surveyed $z=0.41$ cluster Abell 851 has 3-4 times the field emission-line galaxy density (Martin et al. 2000). We find that the MS1512.4+3647 sample is deficient in galaxies with intermediate colors (1.0 $< g-i <$ 2.0) and implied star-formation exponential decay timescales $\tau \sim$ 100 Myr - 1 Gyr that dominate the Abell 851 emission-line galaxy population. Instead, the majority of [OII] emission-line galaxies surrounding the MS1512.4+3647 cluster are blue ($g-i \leq 1.0$) and forming stars in bursts with $\tau < $ 100 Myr. In both samples, galaxies with the shortest star-formation timescales are preferentially among the faintest star-forming objects. Their i luminosities are consistent with young stellar populations $\sim 10^8 - 10^9 \Msun$, although an additional factor of ten in stellar mass could be hiding in underlying old stellar populations. We discuss the implications for the star-formation histories of dwarf galaxies in the field and rich clusters., Comment: 26 pages, including 5 tables and 13 figures; accepted for publication in the Astrophysical Journal

The specific globular cluster frequencies (S_N) for 24 dwarf elliptical (dE) galaxies in the Virgo and Fornax Clusters and the Leo Group imaged with the Hubble Space Telescope are presented. Combining all available data, we find that for nucleated dEs --- which are spatially distributed like giant ellipticals in galaxy clusters --- S_N(dE,N)=6.5 +- 1.2 and S_N increases with M_V, while for non-nucleated dEs --- which are distributed like late-type galaxies --- S_N(dE,noN)=3.1 +- 0.5 and there is little or no trend with M_V. The S_N values for dE galaxies are thus on average significantly higher than those for late-type galaxies, which have S_N < 1. This suggests that dE galaxies are more akin to giant Es than to late-type galaxies. If there are dormant or stripped irregulars hiding among the dE population, they are likely to be among the non-nucleated dEs. Furthermore, the similarities in the properties of the globular clusters and in the spatial distributions of dE,Ns and giant Es suggest that neither galaxy mass or galaxy metallicity is responsible for high values of S_N. Instead, most metal-poor GCs may have formed in dwarf-sized fragments that merged into larger galaxies., Comment: 12 pages (uses aaspp4.sty), 2 figures, 1 table, to appear in the Astrophysical Journal

We present near-IR images of six passive galaxies (SSFR< 10(exp -2)/ Gyr) at redshift 1.3 < z < 2.4 with stellar mass M approximately 10(exp 11) solar M, selected from the Great Observatories Origins Deep Survey (GOODS), obtained with the Hubble Space Telescope (HST) and the WFC3/IR camera. These images provide the deepest and highest angular resolution view of the optical rest-frame morphology of such systems to date. We find that the light profile of these galaxies is generally regular and well described by a Sersic model with index typical of today's spheroids. We confirm the existence of compact and massive early-type galaxies at z approximately 2: four out of six galaxies have r(sub e) approximately 1 kpc or less. The images reach limiting surface brightness mu approximates 26.5 mag/square arcsec in the F160W bandpass; yet there is no evidence of a faint halo in the galaxies of our sample, even in their stacked image. We also find very weak "morphological k-correction" in the galaxies between the rest-frame UV (from the ACS z-band), and the rest-frame optical (WFC3 H-band): the visual classification, Sersic indices and physical sizes of these galaxies are independent or only mildly dependent on the wavelength, within the errors. The presence of an active nucleus is suspected in two out of six galaxies (33%), opening the intriguing possibility that a large, presently unaccounted population of AGN is hosted in these galaxies, possibly responsible for the cessation of star formation.