Search

In the first billion years after the Big Bang, sources of ultraviolet (UV) photons are believed to have ionized intergalactic hydrogen, rendering the Universe transparent to UV radiation. Galaxies brighter than the characteristic luminosity $L^{*}$ do not provide enough ionizing photons to drive this cosmic reionization. Fainter galaxies are thought to dominate the photon budget; however they are surrounded by neutral gas that prevents the escape of the Lyman-$\alpha$ photons, which has been the dominant way to identify them so far. JD1 was previously identified as a triply-imaged galaxy with a magnification factor of 13 provided by the foreground cluster Abell 2744, and a photometric redshift of $z\sim10$. Here we report the spectroscopic confirmation of this very low luminosity ($\sim0.05 L^{*}$) galaxy at $z=9.79$, observed 480 Myr after the Big Bang, by means of the identification of the Lyman break and redward continuum, as well as multiple $\gtrsim4\sigma$ emission lines, with the Near-InfraRed Spectrograph (NIRSpec) and Near-InfraRed Camera (NIRCam) instruments. The combination of the James Webb Space Telescope (JWST) and gravitational lensing shows that this ultra-faint galaxy ($M_{\rm UV}=-17.35$) -- with a luminosity typical of the sources responsible for cosmic reionization -- has a compact ($\sim$150 pc) and complex morphology, low stellar mass (10$^{7.19}$ M$_\odot$), and subsolar ($\sim$0.6 $Z_{\odot}$) gas-phase metallicity., Comment: Matched to the published Nature version of the article. 19 pages, 4 main figures, 1 supplementary figure, 1 supplementary tables. This version includes an updated version of the NIRSpec spectrum and NIRCam photometry

The Near Infrared Camera for the James Webb Space Telescope (JWST) is delivering the imagery that astronomers have hoped for ever since JWST was proposed back in the 1990s. In the Commissioning Period that extended from right after launch to early 2022 July, NIRCam has been subjected to a number of performance tests and operational checks. The camera is exceeding prelaunch expectations in virtually all areas, with very few surprises discovered in flight. NIRCam also delivered the imagery needed by the Wavefront Sensing Team for use in aligning the telescope mirror segments.

Finding and characterising the first galaxies that illuminated the early Universe at cosmic dawn is pivotal to understand the physical conditions and the processes that led to the formation of the first stars. In the first few months of operations, imaging from the James Webb Space Telescope (JWST) have been used to identify tens of candidates of galaxies at redshift (z) greater than 10, less than 450 million years after the Big Bang. However, none of these candidates has yet been confirmed spectroscopically, leaving open the possibility that they are actually low-redshift interlopers. Here we present spectroscopic confirmation and analysis of four galaxies unambiguously detected at redshift 10.3, Comment: 32 pages, 8 figures, accepted to Nature Astronomy

Galaxy protoclusters, which will eventually grow into the massive clusters we see in the local universe, are usually traced by locating overdensities of galaxies. Large spectroscopic surveys of distant galaxies now exist, but their sensitivity depends mainly on a galaxy's star formation activity and dust content rather than its mass. Tracers of massive protoclusters that do not rely on their galaxy constituents are therefore needed. Here we report observations of Lyman-$\alpha$ absorption in the spectra of a dense grid of background galaxies, which we use to locate a substantial number of candidate protoclusters at redshifts 2.2-2.8 via their intergalactic gas. We find that the structures producing the most absorption, most of which were previously unknown, contain surprisingly few galaxies compared to the dark matter content of their analogs in cosmological simulations. Nearly all are expected to be protoclusters, and we infer that half of their expected galaxy members are missing from our survey because they are unusually dim at rest-frame ultraviolet wavelengths. We attribute this to an unexpectedly strong and early influence of the protocluster environment on the evolution of these galaxies that reduced their star formation or increased their dust content., Comment: Published in Nature. The version of record is available at https://www.nature.com/articles/s41586-022-04681-6 or view-only at https://rdcu.be/cPIIX

Galaxy protoclusters, which will eventually grow into the massive clusters we see in the local Universe, are usually traced by locating overdensities of galaxies

A key obstacle to developing a satisfying theory of galaxy evolution is the difficulty in extending analytic descriptions of early structure formation into full nonlinearity, the regime in which galaxy growth occurs. Extant techniques, though powerful, are based on approximate numerical methods whose Monte Carlo-like nature hinders intuition building. Here, we develop a new solution to this problem and its empirical validation. We first derive closed-form analytic expectations for the evolution of fixed percentiles in the real-space cosmic density distribution, {\it averaged over representative volumes observers can track cross-sectionally\}. Using the Lagrangian forms of the fluid equations, we show that percentiles in $\delta$---the density relative to the median---should grow as $\delta(t)\propto\delta_{0}^{\alpha}\,t^{\beta}$, where $\alpha\equiv2$ and $\beta\equiv2$ for Newtonian gravity at epochs after the overdensities transitioned to nonlinear growth. We then use 9.5 sq. deg. of Carnegie-Spitzer-IMACS Redshift Survey data to map {\it galaxy\} environmental densities over $0.2, Comment: 13 pages, 12 figures, submitted to Monthly Notices of the Royal Astronomical Society, 23 August 2019, and accepted for publication, 9 January 2020. Some more typo(s) fixed

We introduce LATIS, the Ly$\alpha$ Tomography IMACS Survey, a spectroscopic survey at Magellan designed to map the z=2.2-2.8 intergalactic medium (IGM) in three dimensions by observing the Ly$\alpha$ forest in the spectra of galaxies and QSOs. Within an area of 1.7 deg${}^2$, we will observe approximately half of $\gtrsim L^*$ galaxies at z=2.2-3.2 for typically 12 hours, providing a dense network of sightlines piercing the IGM with an average transverse separation of 2.5 $h^{-1}$ comoving Mpc (1 physical Mpc). At these scales, the opacity of the IGM is expected to be closely related to the dark matter density, and LATIS will therefore map the density field in the $z \sim 2.5$ universe at $\sim$Mpc resolution over the largest volume to date. Ultimately LATIS will produce approximately 3800 spectra of z=2.2-3.2 galaxies that probe the IGM within a volume of $4 \times 10^6 h^{-3}$ Mpc${}^3$, large enough to contain a representative sample of structures from protoclusters to large voids. Observations are already complete over one-third of the survey area. In this paper, we describe the survey design and execution. We present the largest IGM tomographic maps at comparable resolution yet made. We show that the recovered matter overdensities are broadly consistent with cosmological expectations based on realistic mock surveys, that they correspond to galaxy overdensities, and that we can recover structures identified using other tracers. LATIS is conducted in Canada-France-Hawaii Telescope Legacy Survey fields, including COSMOS. Coupling the LATIS tomographic maps with the rich data sets collected in these fields will enable novel studies of environment-dependent galaxy evolution and the galaxy-IGM connection at cosmic noon.

Late bloomers are massive ($M_* >10^{10}\,M_\odot$) galaxies at $z, 27 pages, 16 figures, 4 tables, 1 ancillary data file (.xml input file to generate GALACTICUS SAM results). Accepted to ApJ. Revises previous (submitted) version; results unchanged

We present the Morphology-Density and Morphology-Radius relations (T-Sigma and T-R, respectively) obtained from the WINGS database of galaxies in nearby clusters. Aiming to achieve the best statistics, we exploit the whole sample of galaxies brighter than MV=-19.5 (5,504 objects), stacking up the 76 clusters of the WINGS survey altogether. Using this global cluster sample, we find that the T-Sigma relation holds only in the inner cluster regions (R, 21 pages, 17 figures, 7 tables, accepted for publication in MNRAS, online material at: ftp://ftp.oapd.inaf.it/pub/fasano/maps.pdf

Modern data empower observers to describe galaxies as the spatially and biographically complex objects they are. We illustrate this through case studies of four, $z\sim1.3$ systems based on deep, spatially resolved, 17-band + G102 + G141 Hubble Space Telescope grism spectrophotometry. Using full spectrum rest-UV/-optical continuum fitting, we characterize these galaxies' observed $\sim$kpc-scale structures and star formation rates (SFRs) and reconstruct their history over the age of the universe. The sample's diversity---passive to vigorously starforming; stellar masses $\log M_*/M_\odot=10.5$ to $11.2$---enables us to draw spatio-temporal inferences relevant to key areas of parameter space (Milky Way- to super-Andromeda-mass progenitors). Specifically, we find signs that bulge mass-fractions ($B/T$) and SF history shapes/spatial uniformity are linked, such that higher $B/T$s correlate with "inside-out growth" and central specific SFRs that peaked above the global average for all starforming galaxies at that epoch. Conversely, the system with the lowest $B/T$ had a flat, spatially uniform SFH with normal peak activity. Both findings are consistent with models positing a feedback-driven connection between bulge formation and the switch from rising to falling SFRs ("quenching"). While sample size forces this conclusion to remain tentative, this work provides a proof-of-concept for future efforts to refine or refute it: JWST, WFIRST, and the 30-m class telescopes will routinely produce data amenable to this and more sophisticated analyses. These samples---spanning representative mass, redshift, SFR, and environmental regimes---will be ripe for converting into thousands of sub-galactic-scale empirical windows on what individual systems actually looked like in the past, ushering in a new dialog between observation and theory., Comment: 18 pp, 15 figs, 3 tables (main text); 5 pp, 5 figs, 1 table (appendix); Submitted to AAS Journals 1 October 2017

Exploiting the data of the Grism Lens-Amplified Survey from Space (GLASS), we characterize the spatial distribution of star formation in 76 high star forming galaxies in 10 clusters at 0.3< z, Comment: ApJ in press (16 pages, 8 figures)

International audience; We present the results of a systematic search for Lyα emitters (LAEs) at $6\lesssim z\lesssim 7.6$ using the HST WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our total volume over this redshift range is $\sim 8\times {10}^{5}$ Mpc(3), comparable to many of the narrowband surveys despite their larger area coverage. We find two LAEs at z = 6.38 and 6.44 with line luminosities of ${L}_{\mathrm{Ly}\alpha }\sim 4.7\times {10}^{43}$ erg s(−)(1), putting them among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule out almost all lower-redshift contaminants. The WISP LAEs have a high number density of $7.7\times {10}^{-6}$ Mpc(−)(3). We argue that the LAEs reside in megaparsec-scale ionized bubbles that allow the Lyα photons to redshift out of resonance before encountering the neutral intergalactic medium. We discuss possible ionizing sources and conclude that the observed LAEs alone are not sufficient to ionize the bubbles.

We have learned much about galaxy evolution since z = 2, and something to even higher redshifts. How can it be that we know so little about! the star formation histories (SFHs) of individual galaxies? Although great progress has been made accumulating huge samples with only rudimentary properties, progress in galaxy evolution means connecting what we've learned to detailed measurements of the life-histories of specific –- not just representative –- systems.

Exploiting the slitless spectroscopy taken as part of the Grism Lens-Amplified Survey from Space (GLASS), we present an extended analysis of the spatial distribution of star formation in 76 galaxies in 10 clusters at 0.3< z, Comment: ApJ in press (22 pages, 21 figures)

We present near-infrared emission line counts and luminosity functions from the HST WFC3 Infrared Spectroscopic Parallels (WISP) program for 29 fields (0.037 deg^2) observed using both the G102 and G141 grisms. Altogether we identify 1048 emission line galaxies with observed equivalent widths greater than 40 Angstroms, 467 of which have multiple detected emission lines. The WISP survey is sensitive to fainter flux levels (3-5x10^-17 ergs/s/cm^2) than the future space near-infrared grism missions aimed at baryonic acoustic oscillation cosmology (1-4x10^-16 ergs/s/cm^2), allowing us to probe the fainter emission line galaxies that the shallower future surveys may miss. Cumulative number counts of 0.7, Comment: 18 pages, 14 figures, Accepted by ApJ

Spectroscopic observations of Hα and Hβ emission lines of 128 star-forming galaxies in the redshift range 0.75 ≤ z ≤ 1.5 are presented. These data were taken with slitless spectroscopy using the G102 and G141 grisms of the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of the WFC3 Infrared Spectroscopic Parallel survey. Interstellar dust extinction is measured from stacked spectra that cover the Balmer decrement (Hα/Hβ). We present dust extinction as a function of Hα luminosity (down to 3 × 1041 erg s-1), galaxy stellar mass (reaching 4 × 108 M, and rest-frame Hα equivalent width. The faintest galaxies are two times fainter in Hα luminosity than galaxies previously studied at z ∼ 1.5. An evolution is observed where galaxies of the same Hα luminosity have lower extinction at higher redshifts, whereas no evolution is found within our error bars with stellar mass. The lower Hα luminosity galaxies in our sample are found to be consistent with no dust extinction. We find an anti-correlation of the [O III] λ5007/Hα flux ratio as a function of luminosity where galaxies with L Hα < 5 × 1041 erg s-1 are brighter in [O III] λ5007 than Hα. This trend is evident even after extinction correction, suggesting that the increased [O III] λ5007/Hα ratio in low-luminosity galaxies is likely due to lower metallicity and/or higher ionization parameters. © 2013. The American Astronomical Society. All rights reserved..

Knowledge of galaxy evolution rests on cross-sectional observations of different objects at different times. Understanding of galaxy evolution rests on longitudinal interpretations of how these data relate to individual objects moving through time. The connection between the two is often assumed to be clear, but we use a simple "physics-free" model to show that it is not, and that exploring its nuances can yield new insights. Comprising nothing more than $2094$ loosely constrained lognormal star formation histories (SFHs), the model faithfully reproduces the following data it was not designed to match: stellar mass functions at $z\leq8$; the slope of the star formation rate/stellar mass relation (the SF "Main Sequence") at $z\leq6$; the mean ${\rm sSFR}(\equiv{\rm SFR}/M_*)$ of low-mass galaxies at $z\leq7$; "fast-" and "slow-track" quenching; downsizing; and a correlation between formation timescale and ${\rm sSFR}(M_*; t)$ similar to results from simulations that provides a natural connection to bulge growth. We take these findings---which suggest that quenching is the natural downturn of all SFHs affecting galaxies at rates/times correlated with their densities---to mean that: (1) models in which galaxies are diversified on Hubble timescales by something like initial conditions rival the dominant grow-and-quench framework as good descriptions of the data; or (2) absent spatial information, many metrics of galaxy evolution are too undiscriminating---if not inherently misleading---to confirm a unique explanation. We outline future tests of our model but stress that, even if ultimately incorrect, it illustrates how exploring different paradigms can aid learning and, we hope, more detailed modeling efforts., 25 pages, 18 figures (including appendices); Accepted to ApJ (ApJ, 832, 7A). This version incorporates minor revisions from the refereeing process, including the addition of one new figure ("C1") and appendix ("C"). All original results are unchanged

We reexamine the systematic properties of local galaxy populations, using published surveys of star formation, structure, and gas content. After recalibrating star formation measures, we are able to reliably measure specific star formation rates well below the "main sequence" of star formation vs mass. We find an unexpectedly large population of galaxies with star formation rates intermediate between vigorously star-forming main sequence galaxies and passive galaxies, and with gas content disproportionately high for their star formation rates. Several lines of evidence suggest that these quiescent galaxies form a distinct population rather than a low star formation tail of the main sequence. We demonstrate that a tight main sequence, evolving with epoch, is a natural outcome of most histories of star formation and has little astrophysical significance, but that the quiescent population requires additional astrophysics to explain its properties. Using a simple model for disk evolution based on the observed dependence of star formation on gas content in local galaxies, and assuming simple histories of cold gas inflow, we show that the evolution of galaxies away from the main sequence can be attributed to the depletion of gas due to star formation after a cutoff in gas inflow. The quiescent population is composed of galaxies in which the density of disk gas has fallen below a threshold for disk stability. The evolution of galaxies beyond the quiescent state to gas exhaustion requires another process, probably wind-driven mass loss. The SSFR distribution of the quiescent and passive implies that the timescale of this process must be greater than a few Gyrs but less than a few tens of Gyrs. The environmental dependence of the galaxy populations is consistent with recent theory suggesting that cold gas inflows into galaxies are truncated at earlier times in denser environments., Comment: 18 pages, 21 figures, submitted to ApJ Figure 3 replaced with correct file

Using deep Hubble Frontier Fields imaging and slitless spectroscopy from the Grism Lens-Amplified Survey from Space, we analyze 2200 cluster and 1748 field galaxies at $0.2\leq z\leq0.7$ to determine the impact of environment on galaxy size and structure at $\log M_*/M_\odot>7.8$, an unprecedented limit at these redshifts. Based on simple assumptions-$r_e=f(M_*)$-we find no significant differences in half-light radii ($r_e$) between equal-mass cluster or field systems. More complex analyses-$r_e=f(M_*,U-V,n,z,\Sigma$)-reveal local density $(\Sigma$) to induce only a $7\% \pm 3\%$ ($95\%$ confidence) reduction in $r_e$ beyond what can be accounted for by $U-V$ color, Sersic index ($n$), and redshift ($z$) effects.Almost any size difference between galaxies in high- and low-density regions is thus attributable to their different distributions in properties other than environment. Indeed, we find a clear color-$r_e$ correlation in low-mass passive cluster galaxies ($\log M_*/M_\odot, Comment: The accepted version. The catalog is available through the GLASS web page (http://glass.astro.ucla.edu), or https://www.astr.tohoku.ac.jp/~mtakahiro/Publication/Morishita17/

WINGS is a wide-field multi-wavelength survey of 76 X-ray selected clusters at low redshift. The WINGS database has been used for a variety of cluster and cluster galaxy studies, investigating galaxy star formation, morphologies, structure, stellar mass functions and other properties. We present the recent wider-field extension of WINGS, OMEGAWINGS, conducted with OmegaCAM@VST and AAOmega@AAT. We show two of our latest results regarding jellyfish galaxies and galaxy sizes. OMEGAWINGS has allowed the first systematic search of galaxies with signs of ongoing ram pressure stripping (jellyfishes), yielding a catalog of \(\sim\) 240 galaxies in 41 clusters. We discuss the first results obtained from this sample and the prospects for integral field data. Finally, we summarize our results regarding the discovery of compact massive galaxies at low redshift, their properties, dependence on environment and the implications for the evolution of galaxy sizes from high- to low-z.

We present coarse but robust star formation histories (SFHs) derived from spectro-photometric data of the Carnegie-Spitzer-IMACS Survey, for 22,494 galaxies at 0.3, Comment: 17 pages, 10 figures; accepted by ApJ; version 2 - no substantive changes; clarifications and corrections

We present the morphological catalog of galaxies in nearby clusters of the WINGS survey (Fasano et al. 2006). The catalog contains a total number of 39923 galaxies, for which we provide the automatic estimates of the morphological type applying the purposely devised tool MORPHOT to the V-band WINGS imaging. For ~3000 galaxies we also provide visual estimates of the morphological types. A substantial part of the paper is devoted to the description of the MORPHOT tool, whose application is limited, at least for the moment, to the WINGS imaging only. The approach of the tool to the automation of morphological classification is a non parametric and fully empiri- cal one. In particular, MORPHOT exploits 21 morphological diagnostics, directly and easily computable from the galaxy image, to provide two independent classifications: one based on a Maximum Likelihood (ML), semi-analytical technique, the other one on a Neural Network (NN) machine. A suitably selected sample of ~1000 visually clas- sified WINGS galaxies is used to calibrate the diagnostics for the ML estimator and as a training set in the NN machine. The final morphological estimator combines the two techniques and proves to be effective both when applied to an additional test sample of ~1000 visually classified WINGS galaxies and when compared with small samples of SDSS galaxies visually classified by Fukugita et al. (2007) and Nair et al. (2010). Finally, besides the galaxy morphology distribution (corrected for field contamination) in the WINGS clusters, we present the ellipticity ({\epsilon}), color (B-V) and Sersic index (n) distributions for different morphological types, as well as the morphological fractions as a function of the clustercentric distance (in units of R200).

Exploiting the capabilities of four different surveys --- the Padova-Millennium Galaxy and Group Catalogue (PM2GC), the WIde-field Nearby Galaxy-cluster Survey (WINGS), the IMACS Cluster Building Survey (ICBS) and the ESO Distant Cluster Survey (EDisCS) --- we analyze the galaxy stellar mass distribution as a function of local density in mass-limited samples, in the field and in clusters from low (z>0.04) to high (z

The Inamori-Magellan Areal Camera and Spectrograph (IMACS) is a wide-field, multipurpose imaging spectrograph on the Magellan-Baade telescope at Las Campanas Observatory. IMACS has two channels—f/2 and f/4, each with an 8K × 8K pixel mosaic of CCD detectors, that service the widest range of capabilities of any major spectrograph. These include wide-field imaging at two scales, 0.20'' pixel-1 and 0.11'' pixel-1, single-object and multislit spectroscopy, integral-field spectroscopy with two 5'' × 7'' areas sampled at 0.20'' pixel-1 (Durham IFU), a multiobject echelle (MOE) capable of N ~ 10 simultaneous full-wavelength R ≈ 20,000 spectra, the Maryland-Magellan Tunable Filter (MMTF), and an image-slicing reformatter for dense-pack multislit work (GISMO). Spectral resolutions of 8 < R < 5000 are available through a combination of prisms, grisms, and gratings, and most modes are instantly available in any given IMACS configuration. IMACS has a spectroscopic efficiency over 50% in f/2 multislit mode (instrument only) and, by the AΩ figure of merit (telescope primary surface area times instrument field of view ), IMACS scores 5.7 m2 deg2, compared with 3.1 for VIMOS on VLT3 and with 2.0 for DEIMOS on Keck2. IMACS is the most versatile, and—for wide-field optical spectroscopy—the most powerful spectrograph on the planet.

We present the galaxy stellar mass function (MF) and its evolution in clusters from z~0.8 to the current epoch, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS) (0.04 10^11 M' does not evolve, but below M*~10^10.8 M' the MF at high redshift is flat, while in the Local Universe it flattens out at lower masses. The population of M* = 10^10.2 - 10^10.8 M' galaxies must have grown significantly between z=0.8 and z=0. We analyze the MF of different morphological types (ellipticals, S0s and late-types), and find that also each of them evolves with redshift. All types have proportionally more massive galaxies at high- than at low-z, and the strongest evolution occurs among S0 galaxies. Examining the morphology-mass relation (the way the proportion of galaxies of different morphological types changes with galaxy mass), we find it strongly depends on redshift. At both redshifts, ~40% of the stellar mass is in elliptical galaxies. Another ~43% of the mass is in S0 galaxies in local clusters, while it is in spirals in distant clusters. To explain the observed trends, we discuss the importance of those mechanisms that could shape the MF. We conclude that mass growth due to star formation plays a crucial role in driving the evolution. It has to be accompanied by infall of galaxies onto clusters, and the mass distribution of infalling galaxies might be different from that of cluster galaxies. However, comparing with high-z field samples, we do not find conclusive evidence for such an environmental mass segregation. Our results suggest that star formation and infall change directly the MF of late-type galaxies in clusters and, indirectly, that of early-type galaxies through subsequent morphological transformations.

We present the ellipticity distribution and its evolution for early-type galaxies in clusters from z~0.8 to z~0, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS)(0.04 M_B+1.208z>-21. Analyzing this sample, we do not recover exactly the same results of the mass-limited sample. Hence the selection criteria are crucial to characterize the galaxy properties: the choice of the magnitude-delimited sample implies the loss of many less massive galaxies and so it biases the final results. Moreover, although we are adopting the same selection criteria, our results in the magnitude-delimited sample are also not in agreement with those of Holden et al.(2009). This is due to the fact that our and their low-z samples have a different magnitude distribution because the Holden et al.(2009) sample suffers from incompleteness at faint magnitudes.

Massive quiescent galaxies at z>1 have been found to have small physical sizes, hence to be superdense. Several mechanisms, including minor mergers, have been proposed for increasing galaxy sizes from high- to low-z. We search for superdense massive galaxies in the WIde-field Nearby Galaxy-cluster Survey (WINGS) of X-ray selected galaxy clusters at 0.04 =1.61+/-0.29kpc, a median Sersic index = 3.0+/-0.6, and very old stellar populations with a median mass-weighted age of 12.1+/-1.3Gyr. We calculate a number density of 2.9x10^-2Mpc^-3 for superdense galaxies in local clusters, and a hard lower limit of 1.3x10^-5Mpc^-3 in the whole comoving volume between z = 0.04 and z = 0.07. We find a relation between mass, effective radius and luminosity-weighted age in our cluster galaxies, which can mimic the claimed evolution of the radius with redshift, if not properly taken into account. We compare our data with spectroscopic high-z surveys and find that -when stellar masses are considered- there is consistency with the local WINGS galaxy sizes out to z~2, while a discrepancy of a factor of 3 exists with the only spectroscopic z>2 study. In contrast, there is strong evidence for a large evolution in radius for the most massive galaxies with M*>4x10^11Msol compared to similarly massive galaxies in WINGS, i.e. the BCGs., Comment: 14 pages, 7 figures, 3 tables, accepted for pubblication in ApJ

We observed two fields near M32 with the Advanced Camera for Surveys/High Resolution Channel (ACS/HRC) on board the Hubble Space Telescope (HST). The main field, F1, is 1.8 arcmin from the center of M32; the second field, F2, constrains the M31 background, and is 5.4 arcmin distant. Each field was observed for 16-orbits in each of the F435W (narrow B) and F555W (narrow V) filters. The duration of the observations allowed RR Lyrae stars and other short-period variables to be detected. A population of RR Lyrae stars determined to belong to M32 would prove the existence of an ancient population in that galaxy, a subject of some debate. We detected 17 RR Lyrae variables in F1 and 14 in F2. A 1-sigma upper limit of 6 RR Lyrae variables belonging to M32 is inferred from these two fields alone. Use of our two ACS/WFC parallel fields provides better constraints on the M31 background, however, and implies that $7_{-3}^{+4}$ (68 % confidence interval) RR Lyrae variables in F1 belong to M32. We have therefore found evidence for an ancient population in M32. It seems to be nearly indistinguishable from the ancient population of M31. The RR Lyrae stars in the F1 and F2 fields have indistinguishable mean V-band magnitudes, mean periods, distributions in the Bailey diagram and ratios of RRc to RR(tot) types. However, the color distributions in the two fields are different, with a population of red RRab variables in F1 not seen in F2. We suggest that these might be identified with the detected M32 RR Lyrae population, but the small number of stars rules out a definitive claim., 19 pages, 18 figures, accepted ApJ

We present the star formation rate (SFR) and starburst fraction (SBF) for a sample of field galaxies from the ICBS intermediate-redshift cluster survey. We use [O II] and Spitzer 24 micron fluxes to measure SFRs, and 24 micron fluxes and H-delta absorption to measure of SBFs, for both our sample and a present-epoch field sample from the Sloan Digital Sky Survey (SDSS) and Spitzer Wide-area Infrared Extragalactic (SWIRE) survey. We find a precipitous decline in the SFR since z=1, in agreement with other studies, as well as a corresponding rapid decline in the fraction of galaxies undergoing long-duration moderate-amplitude starbursts. We suggest that the change in both the rate and mode of star formation could result from the strong decrease since z=1 of gas available for star formation., ApJ Letters in press

We quantify the evolution of the spiral, S0 and elliptical fractions in galaxy clusters as a function of cluster velocity dispersion ($\sigma$) and X-ray luminosity ($L_X$) using a new database of 72 nearby clusters from the WIde-Field Nearby Galaxy-cluster Survey (WINGS) combined with literature data at $z=0.5-1.2$. Most WINGS clusters have $\sigma$ between 500 and 1100 $\rm km s^{-1}$, and $L_X$ between 0.2 and $5 \times 10^{44} \rm erg/s$. The S0 fraction in clusters is known to increase with time at the expense of the spiral population. We find that the spiral and S0 fractions have evolved more strongly in lower $\sigma$, less massive clusters, while we confirm that the proportion of ellipticals has remained unchanged. Our results demonstrate that morphological evolution since $z=1$ is not confined to massive clusters, but is actually more pronounced in low mass clusters, and therefore must originate either from secular (intrinsic) evolution and/or from environmental mechanisms that act preferentially in low-mass environments, or both in low- and high-mass systems. We also find that the evolution of the spiral fraction perfectly mirrors the evolution of the fraction of star-forming galaxies. Interestingly, at low-z the spiral fraction anticorrelates with $L_X$. Conversely, no correlation is observed with $\sigma$. Given that both $\sigma$ and $L_X$ are tracers of the cluster mass, these results pose a challenge for current scenarios of morphological evolution in clusters., Comment: ApJ Letters in press - This version has a revised division between ellipticals and S0s, that leads to slightly higher S0 and lower elliptical fractions

We present results from a blind, spectroscopic survey for redshift ~5.7 Lyman-alpha-emitting galaxies using the Inamori Magellan Areal Camera and Spectrograph. A total of ~200 square arcminutes were observed in the COSMOS and LCIRS fields using a narrowband filter, which transmits between atmospheric emission lines at 8190 A, and a mask with 100 longslits. This observing technique provides higher emission-line sensitivity than narrowband imaging and probes larger volumes than strong lensing. We find 170 emission-line galaxies and identify their redshifts spectroscopically. We confirm three Lyman-alpha emitting galaxies (LAEs), the first discovered using multislit-narrowband spectroscopy. Their line profiles are narrow, but fitted models suggest instrinsic, unattenuated widths 400 km/s FWHM. The red wing of the line profiles present features consistent with galactic winds. The star formation rates of these galaxies are at least 5-7 Msun/yr and likely a factor of two higher. We estimate the number density of L .ge. 5e42 erg/s LAEs is 9.0(+12,-4)e-5 Mpc-3 at redshift 5.7 and constrain the Schechter function parameters describing this population. Galaxies fainter than our detection limit may well be the primary source of ionizing photons at redshift ~ 6. We argue, however, that the break luminosity L* is not yet well constrained. If this break luminosity is near our detection limit, and somewhat lower than previous estimates, then the detected LAE population could be responsible for ionizing the intergalactic gas at redshift ~6. We discuss the potential of multislit-narrowband spectroscopy for deeper emission-line surveys.

The largest galaxies, and in particular central galaxies in clusters, offer unique insight into understanding the mechanism for the growth of nuclear black holes. We present Hubble Space Telescope kinematics for NGC1399, the central galaxy in Fornax. We find the best-fit model contains a black hole of 5.1 +-0.7 x 10^8 Msun (at a distance of 21.1 Mpc), a factor of over 2 below the correlation of black hole mass and velocity dispersion. We also find a dramatic signature for central tangential anisotropy. The velocity profiles on adjacent sides 0.5" away from the nucleus show strong bimodality, and the central spectrum shows a large drop in the dispersion. Both of these observations point to an orbital distribution that is tangentially biased. The best-fit orbital model suggests a ratio of the tangential to radial internal velocity dispersions of three. This ratio is the largest seen in any galaxy to date and will provide an important measure for the mode by which the central black hole has grown., Comment: 9 pages, accepted for publication in the Astrophysical Journal

We combine the results from several HST investigations of the central structure of early-type galaxies to generate a large sample of parameterized surface photometry. The studies included were those that used the "Nuker law" to characterize the inner light distributions of the galaxies. The sample comprises WFPC1 and WFPC2 V band observations published earlier by our group, R band WFPC2 photometry of Rest et al., NICMOS H band photometry by Ravindranath et al. and Quillen et al., and the BCG WFPC2 I band photometry of Laine et al. The distribution of the logarithmic slopes of the central profiles strongly affirms that the central structure of elliptical galaxies with Mv < -19 is bimodal, based on both parametric and non-parametric analysis. At the HST resolution limit, most galaxies are either power-law systems, which have steep cusps in surface brightness, or core systems, which have shallow cusps interior to a steeper envelope brightness distribution. A rapid transition between the two forms occurs over the luminosity range -22 < Mv < -20, with cores dominating at the highest luminosities, and power-laws at the lowest. There are a few "intermediate" systems that have both cusp slopes and total luminosities that fall within the core/power-law transition, but they are rare and do not fill in the overall bimodal distribution of cusp slopes. These results are inconsistent with the Ferrarese et al. Virgo Cluster Survey (VCS) analysis. However, using galaxies common to the VCS samples, we demonstrate that the VCS models of the cusps are either a poor match to the observations or consist of forms fitted to the galaxy envelopes and extrapolated inward to the HST resolution limit.

We search for and characterize substructures in the projected distribution of galaxies observed in the wide field CCD images of the 77 nearby clusters of the WIde-field Nearby Galaxy-cluster Survey (WINGS). This sample is complete in X-ray flux in the redshift range 0.04, Comment: A&A accepted - figure 6 is available from http://adlibitum.oats.inaf.it/ramella/WINGSfigs

We give an overview of the Grism Lens Amplified Survey from Space (GLASS), a large Hubble Space Telescope program aimed at obtaining grism spectroscopy of the fields of ten massive clusters of galaxies at redshift z=0.308-0.686, including the Hubble Frontier Fields (HFF). The Wide Field Camera 3 yields near infrared spectra of the cluster cores, covering the wavelength range 0.81-1.69mum through grisms G102 and G141, while the Advanced Camera for Surveys in parallel mode provides G800L spectra of the infall regions of the clusters. The WFC3 spectra are taken at two almost orthogonal position angles in order to minimize the effects of confusion. After summarizing the scientific drivers of GLASS, we describe the sample selection as well as the observing strategy and data processing pipeline. We then utilize MACSJ0717.5+3745, a HFF cluster and the first one observed by GLASS, to illustrate the data quality and the high-level data products. Each spectrum brighter than H_AB=23 is visually inspected by at least two co-authors and a redshift is measured when sufficient information is present in the spectra. Furthermore, we conducted a thorough search for emission lines through all the GLASS WFC3 spectra with the aim of measuring redshifts for sources with continuum fainter than H_AB=23. We provide a catalog of 139 emission-line based spectroscopic redshifts for extragalactic sources, including three new redshifts of multiple image systems (one probable, two tentative). In addition to the data itself we also release software tools that are helpful to navigate the data., ApJ in press. GLASS data available at https://archive.stsci.edu/prepds/glass/ . More info on GLASS available at http://glass.physics.ucsb.edu/

In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z=0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z=1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses., Published in the 6 March 2015 issue of Science; 17 pages, 7 figures, and 3 tables including Supplementary Materials

In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.

Since z~1, the stellar mass density locked in low mass groups and clusters has grown by a factor of ~8. Here we make the first statistical measurements of the stellar mass content of low mass X-ray groups at 0.5, Comment: 6 pages, 4 figures, accepted to ApJ Letters

We present spatially resolved gas-phase metallicity for a system of three galaxies at z=1.85 detected in the Grism Lens-Amplified Survey from Space (GLASS). The combination of HST's diffraction limit and strong gravitational lensing by the cluster MACS J0717+3745 results in a spatial resolution of ~200-300 pc, enabling good spatial sampling despite the intrinsically small galaxy sizes. The galaxies in this system are separated by 50-200 kpc in projection and are likely in an early stage of interaction, evidenced by relatively high specific star formation rates. Their gas-phase metallicities are consistent with larger samples at similar redshift, star formation rate, and stellar mass. We obtain a precise measurement of the metallicity gradient for one galaxy and find a shallow slope compared to isolated galaxies at high redshift, consistent with a flattening of the gradient due to gravitational interaction. An alternative explanation for the shallow metallicity gradient and elevated star formation rate is rapid recycling of metal-enriched gas, but we find no evidence for enhanced gas-phase metallicities which should result from this effect. Notably, the measured stellar masses log(M/Msun) = 7.2-9.1 probe to an order of magnitude below previous mass-metallicity studies at this redshift. The lowest mass galaxy has properties similar to those expected for Fornax at this redshift, indicating that GLASS is able to directly study the progenitors of local group dwarf galaxies on spatially resolved scales. Larger samples from the full GLASS survey will be ideal for studying the effects of feedback, and the time evolution of metallicity gradients. These initial results demonstrate the utility of HST spectroscopy combined with gravitational lensing for characterizing resolved physical properties of galaxies at high redshift., Comment: AJ in press. The GLASS website is at http://glass.physics.ucsb.edu

This is the first paper of a series that will present data and scientific results from the WINGS project, a wide-field, multiwavelength imaging and spectroscopic survey of galaxies in 77 nearby clusters. The sample was extracted from the ROSAT catalogs with constraints on the redshift (0.0420). The global goal of the WINGS project is the systematic study of the local cosmic variance of the cluster population and of the properties of cluster galaxies as a function of cluster properties and local environment. This data collection will allow to define a local 'Zero-Point' reference against which to gauge the cosmic evolution when compared to more distant clusters. The core of the project consists of wide-field optical imaging of the selected clusters in the B and V bands. We have also completed a multi-fiber, medium resolution spectroscopic survey for 51 of the clusters in the master sample. In addition, a NIR (JK) survey of ~50 clusters and an H_alpha + UV survey of some 10 clusters are presently ongoing, while a very-wide-field optical survey has also been programmed. In this paper we briefly outline the global objectives and the main characteristics of the WINGS project. Moreover, the observing strategy and the data reduction of the optical imaging survey (WINGS-OPT) are presented. We have achieved a photometric accuracy of ~0.025mag, reaching completeness to V~23.5. Field size and resolution (FWHM) span the absolute intervals (1.6-2.7)Mpc and (0.7-1.7)kpc, respectively, depending on the redshift and on the seeing. This allows the planned studies to get a valuable description of the local properties of clusters and galaxies in clusters., Comment: 24 pages, 15 figures, Accepted by Astronomy and Astrophysics

We present optical, near-IR, and radio follow up of sixteen Swift bursts, including our discovery of nine afterglows and a redshift determination for three. These observations, supplemented by data from the literature, provide an afterglow recovery rate of 60% in the optical/near-IR, much higher than in previous missions (BeppoSAX, HETE-2, INTEGRAL, and IPN). The optical/near-IR afterglows of Swift events are on average 1.7 mag fainter at t=12 hr than those of previous missions. The X-ray afterglows are similarly fainter compared to those of pre-Swift bursts. In the radio the limiting factor is the VLA threshold and the detection rate for Swift bursts is similar to that for past missions. The redshift distribution of pre-Swift bursts peaked at z~1, whereas the five Swift bursts with measured redshifts are distributed evenly between 1.3 and 3.2. From these results we conclude that (i) the pre-Swift distributions were biased in favor of bright events and low redshift events, (ii) the higher sensitivity and accurate positions of Swift result in a better representation of the true burst redshift and brightness distributions (which are higher and dimmer, respectively), and (iii) as many as 1/3 of the bursts can be optically dark, as a result of a high redshift and/or dust extinction. We remark that the apparent lack of low redshift, low luminosity Swift bursts, and the lower event rate compared to pre-launch estimates (90 vs. 150 per year), are the result of a threshold that is similar to that of BATSE. In view of these inferences, afterglow observers may find it advisable to make significant changes in follow up strategies of Swift events. [abridged]

We investigate the effect of a small contamination of hot, old, metal-poor starlight on the inferred stellar populations of early-type galaxies in the core of the Coma Cluster. We find that the required correction to the Balmer and metal absorption-line strengths for old, metal-poor stars does not significantly affect the inferred age of the stellar population when the Hbeta strength is large. Intermediate-aged populations are therefore still needed to explain enhanced Balmer-line strengths in early-type galaxies. This gives us increased confidence in our age estimates for these objects. For galaxies with weak Balmer-line strengths corresponding to very old populations (t>10 Gyr), however, a correction for hot stars may indeed alter the inferred age, as previously suggested. Finally, the inferred metallicity [Z/H] will always be higher after any correction for old, metal-poor starlight than without, but the enhancement ratios [E/Fe] will strengthen only slightly., 8 pages, 3 figures (2 in color); accepted for publication in MNRAS