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Register a new userThe Grism Lens-Amplified Survey from Space (GLASS). XII. Spatially Resolved Galaxy Star Formation Histories and True Evolutionary Paths at z > 1
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L.E. Abramson
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Modern data empower observers to describe galaxies as the spatially and biographically complex objects they are. We illustrate this through case studies of four, $zsim1.3$ 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 samples 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.
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We present the first study of the spatial distribution of star formation in z~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 (MACS0717.5+3745 and MACS1423.8+2404) with different morphologies (one relaxed and one merging) and use foreground and background galaxies as field control sample. The cluster+field sample consists of 42 galaxies with stellar masses in the range 10^8-10^11 M_sun, and star formation rates in the range 1-20 M_sun/yr. 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 ~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 process that regulate star formation. Upcoming analysis of the full GLASS dataset will increase our sample size by almost an order of magnitude, verifying and strengthening the inference from this initial dataset.
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.
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_sun) and star formation rate (0.5-50 M_sun/yr). We visually classify galaxies in terms of broad-band morphology, Halpha morphology and likely physical process acting on the galaxy. Most Halpha 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 Halpha 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 subtle. A full understanding of this complexity requires larger samples and detailed and spatially resolved physical models.
We present a catalogue of 22755 objects with slitless, optical, Hubble Space Telescope (HST) spectroscopy from the Grism Lens-Amplified Survey from Space (GLASS). The data cover $sim$220 sq. arcmin to 7-orbit ($sim$10 ks) depth in 20 parallel pointings of the Advanced Camera for Surveys G800L grism. The fields are located 6 away from 10 massive galaxy clusters in the HFF and CLASH footprints. Thirteen of the fields have ancillary HST imaging from these or other programs to facilitate a large number of applications, from studying metal distributions at $zsim0.5$, to quasars at $zsim4$, to the star formation histories of hundreds of galaxies in between. The spectroscopic catalogue has a median redshift of $langle zrangle=0.6$ with a median uncertainty of $Delta z / (1+z)lesssim2%$ at $rm F814Wlesssim23$ AB. Robust continuum detections reach a magnitude fainter. The 5 $sigma$ limiting line flux is $f_{rm lim}approx5times10^{-17}rm~erg~s^{-1}~cm^{-2}$ and half of all sources have 50% of pixels contaminated at $lesssim$1%. All sources have 1- and 2-D spectra, line fluxes/uncertainties and identifications, redshift probability distributions, spectral models, and derived narrow-band emission line maps from the Grism Redshift and Line Analysis tool (GRIZLI). We provide other basic sample characterisations, show data examples, and describe sources and potential investigations of interest. All data and products will be available online along with software to facilitate their use.
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 <0.7. All 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 this offsets into a radial and tangential component. The radial compo- nent points away from the cluster center in 60% of the cases, with 95% confidence. The decompositions agree with cosmological simulations, i.e. 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, correla- tions 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.
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