Upcoming space-based surveys such as Euclid and WFIRST-AFTA plan to measure baryonic acoustic oscillations in order to study dark energy. These surveys will use IR slitless grism spectroscopy to measure redshifts of a large number of galaxies over a significant redshift range. In this paper, we use the Wide Field Camera 3 Infrared Spectroscopic Parallel Survey (WISP) to estimate the expected number of H alpha emitters observable by these future surveys. WISP is an ongoing Hubble Space Telescope slitless spectroscopic survey, covering the 0.8-1.65 mu m wavelength range and allowing the detection of H alpha emitters up to z similar to 1.5 and [O III] emitters to z similar to 2.3. We derive the H alpha-[O III] bivariate line luminosity function (LLF) for WISP galaxies at z similar to 1 using a maximum likelihood estimator that properly accounts for uncertainties in line luminosity measurements and we demonstrate how it can be used to derive the H alpha luminosity function by exclusively fitting [O III] data. Using the z similar to 2 [O III] LLF and assuming that the relation between H alpha and [O III] luminosity does not change significantly over the redshift range, we predict the H alpha number counts at z similar to 2-the upper end of the redshift range of interest for future surveys. For the redshift range 0.7 < z < 2, we expect similar to 3000 galaxies deg(-2) for a flux limit of 3 x 10(-16) erg s(-1) cm(-2) (the proposed depth of the Euclid galaxy redshift survey) and similar to 20,000 galaxies deg(-2) for a flux limit of similar to 10(-16) erg s(-1) cm(-2) (the baseline depth of the WFIRST galaxy redshift survey).

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 10 massive clusters of galaxies at redshift z = 0.308-0.686, including the Hubble Frontier Fields (HFF). The Wide Field Camera 3 (WFC3) yields nearinfrared spectra of the cluster cores covering the wavelength range 0.81-1.69 mu m 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 MACS J0717.5+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 of 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.

We present a census of Ly alpha emission at z greater than or similar to 7, utilizing deep near-infrared Hubble Space Telescope grism spectroscopy from the first six completed clusters of the Grism Lens-Amplified Survey from Space (GLASS). In 24/159 photometrically selected galaxies we detect emission lines consistent with Ly alpha in the GLASS spectra. Based on the distribution of signal-to-noise ratios and on simulations, we expect the completeness and the purity of the sample to be 40%-100% and 60%-90%, respectively. For the objects without detected emission lines we show that the observed (not corrected for lensing magnification) 1 sigma flux limits reach 5 x 10(-18) erg s(-1) cm(-2) per position angle over the full wavelength range of GLASS (0.8-1.7 mu m). Based on the conditional probability of Ly alpha emission measured from the ground at z similar to 7, we would have expected 12-18 Ly alpha emitters. This is consistent with the number of detections, within the uncertainties, confirming the drop in Ly alpha emission with respect to z similar to 6. Deeper follow-up spectroscopy, here exemplified by Keck spectroscopy, is necessary to improve our estimates of completeness and purity. and to confirm individual candidates as true Ly alpha emitters. These candidates include a promising source at z = 8.1. The spatial extent of Ly alpha in a deep stack of the most convincing Ly alpha emitters with < z > = 7.2 is consistent with that of the rest-frame UV continuum. Extended Ly alpha emission, if present, has a surface brightness below our detection limit, consistent with the properties of lower-redshift comparison samples. From the stack we estimate upper limits on rest-frame UV emission line ratios and find f(C IV)/f(Ly alpha) less than or similar to 0.32 and f(C III])/f(Ly alpha) less than or similar to 0.23, in good agreement with other values published in the literature.

We present the first study of the spatial distribution of star formation in z similar to 0.5 cluster galaxies. The analysis is based on data taken with the Wide Field Camera 3 as part of the Grism Lens-Amplified Survey from Space (GLASS). We illustrate the methodology by focusing on two clusters (MACS 0717.5+3745 and MACS 1423.8 + 2404) with different morphologies (one relaxed and one merging) and use foreground and background galaxies as a field control sample. The cluster+field sample consists of 42 galaxies with stellar masses in the range 10(8)-10(11) M-circle dot and star formation rates in the range 1-20 M-circle dot yr(-1). Both in clusters and in the field, H alpha is more extended than the rest-frame UV continuum in 60% of the cases, consistent with diffuse star formation and inside-out growth. In similar to 20% of the cases, the H alpha emission appears more extended in cluster galaxies than in the field, pointing perhaps to ionized gas being stripped and/or star formation being enhanced at large radii. The peak of the H alpha emission and that of the continuum are offset by less than 1 kpc. We investigate trends with the hot gas density as traced by the X-ray emission, and with the surface mass density as inferred from gravitational lens models, and find no conclusive results. The diversity of morphologies and sizes observed in H alpha illustrates the complexity of the environmental processes that regulate star formation. Upcoming analysis of the full GLASS data set will increase our sample size by almost an order of magnitude, verifying and strengthening the inference from this initial data set.

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. I and galaxy sizes. OMEGAWINGS has allowed the first systematic search of galaxies with signs of ongoing ram pressure stripping (jellyfishes), yielding a catalog of similar to 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.

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 < 0.7. We use 85 foreground and background galaxies in the same redshift range as a field sample. The samples are well matched in stellar mass (10(8)-10(11) M-circle dot) and star formation rate (0.550 M-circle dot yr(-1)). We visually classify galaxies in terms of broad band morphology, Ha morphology, and likely physical process acting on the galaxy. Most Ha emitters have a spiral morphology (41% +/- 8% in clusters, 51% +/- 8% in the field), followed by mergers/interactions (28% +/- 8%, 31% +/- 7%, respectively) and early-type galaxies (remarkably as high as 29% +/- 8% in clusters and 15% +/- 6% in the field). A diversity of Ha morphologies is detected, suggesting a diversity of physical processes. In clusters, 30% +/- 8% of the galaxies present a regular morphology, mostly consistent with star formation diffused uniformly across the stellar population (mostly in the disk component, when present). The second most common morphology (28% +/- 8%) is asymmetric/jellyfish, consistent with ram-pressure stripping or other non-gravitational processes in 18% +/- 8% of the cases. Ram-pressure stripping appears significantly less prominent in the field (2% +/- 2%), where the most common morphology/mechanism appears to be consistent with minor gas-rich mergers or clump accretion. This work demonstrates that while environment-specific mechanisms affect galaxy evolution at this redshift, they are diverse and their effects are subtle. A full understanding of this complexity requires larger samples and detailed and spatially resolved physical models.

Using deep Hubble Frontier Fields imaging and slitless spectroscopy from the Grism Survey from Space, we study 2200 cluster and 1748 field galaxies at 0.2 <= z <= 0.7 to determine the impact of environment on galaxy size and structure at stellar masses logM(*)/M-circle dot > 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 (S) to induce only a 7% +/- 3% (95% confidence) reduction in re 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-re correlation in low-mass passive cluster galaxies (logM(*)/M-circle dot < 9.8) such that bluer systems have larger radii, with the bluest having sizes consistent with equal-mass star-forming galaxies. We take this as evidence that large-re low-mass passive cluster galaxies are recently acquired systems that have been environmentally quenched without significant structural transformation (e.g., by ram pressure stripping or starvation). Conversely, similar to 20% of small-r(e) low-mass passive cluster galaxies appear to have been in place since z greater than or similar to 3. Given the consistency of the small-r(e) galaxies' stellar surface densities (and even colors) with those of systems more than ten times as massive, our findings suggest that clusters mark places where galaxy evolution is accelerated for an ancient base population spanning most masses, with late-time additions quenched by environment-specific mechanisms mainly restricted to the lowest masses.

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 <= 8; the slope of the star formation rate/stellar mass relation (the SFR "Main Sequence") at z <= 6; the mean sSFR(equivalent to SFR/M-*) of low-mass galaxies at z <= 7; "fast-" and "slow-track" quenching; downsizing; and a correlation between formation timescale and 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.

Exploiting the data of the Grism Lens-Amplified Survey from Space (GLASS), we characterize the spatial distribution of star formation in 76 highly active star-forming galaxies in 10 clusters at 0.3 < z < 0.7. All of these galaxies are likely restricted to first infall. In a companion paper, we contrast the properties of field and cluster galaxies, whereas here we correlate the properties of H alpha emitters to a number of tracers of the cluster environment to investigate its role in driving galaxy transformations. H alpha emitters are found in the clusters out to 0.5 virial radii, the maximum radius covered by GLASS. The peak of the H alpha emission is offset with respect to the peak of the UV continuum. We decompose these offsets into a radial and a tangential component. The radial component points away from the cluster center in 60% of the cases, with 95% confidence. The decompositions agree with cosmological simulations; that is, the H alpha emission offset correlates with galaxy velocity and ram-pressure stripping signatures. Trends between H alpha emitter properties and surface mass density distributions and X-ray emissions emerge only for unrelaxed clusters. The lack of strong correlations with the global environment does not allow us to identify a unique environmental effect originating from the cluster center. In contrast, correlations between H alpha morphology and local number density emerge. We conclude that local effects, uncorrelated to the cluster-centric radius, play a more important role in shaping galaxy properties.

We reexamine the 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 that of the so-called "main sequence" of star formation versus mass. We find an unexpectedly large population of quiescent galaxies with star formation rates intermediate between the main sequence and passive populations and with disproportionately high star formation rates. We demonstrate that a tight main sequence 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 of gas inflow. The quiescent population is composed of galaxies in which the density of disk gas has fallen below a threshold for star formation probably set by disk stability. The evolution of galaxies beyond the quiescent state to gas exhaustion and the end of star formation requires another process, probably wind-driven mass loss. The environmental dependence of the three galaxy populations is consistent with recent numerical modeling, which indicates that cold gas inflows into galaxies are truncated at earlier epochs in denser environments.