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Register a new userThe Grism Lens-Amplified Survey from Space (GLASS). XI. Detection of CIV in Multiple Images of $z=6.11$ Ly$alpha$ Emitter Behind RXCJ2248.7-4431
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The CIII] and CIV rest-frame UV emission lines are powerful probes of the ionizations states of galaxies. They have furthermore been suggested as alternatives for spectroscopic redshift confirmation of objects at the epoch of reionization ($z>6$), where the most frequently used redshift indicator, Ly$alpha$, is attenuated by the high fraction of neutral hydrogen in the inter-galactic medium. However, currently only very few confirmations of carbon UV lines at these high redshifts exist, making it challenging to quantify these claims. Here, we present the detection of CIV$lambdalambda$1548,1551AA in HST slitless grism spectroscopy obtained by GLASS of a Ly$alpha$ emitter at $z=6.11$ multiply imaged by the massive foreground galaxy cluster RXJ2248. The CIV emission is detected at the 3--5$sigma$ level in two images of the source, with marginal detection in two other images. We do not detect significant CIII]$lambdalambda$1907,1909AA emission implying an equivalent width EW$_textrm{CIII]}<20$AA (1$sigma$) and $textrm{CIV/CIII}>0.7$ (2$sigma$). Combined with limits on the rest-frame UV flux from the HeII$lambda$1640AA emission line and the OIII]$lambdalambda$1661,1666AA doublet, we put constraints on the metallicity and the ionization state of the galaxy. The estimated line ratios and equivalent widths do not support a scenario where an AGN is responsible for ionizing the carbon atoms. SED fits including nebular emission lines imply a source with a mass of log(M/M$_odot)sim9$, SFR of around 10M$_odot$/yr, and a young stellar population $<50$Myr old. The source shows a stronger ionizing radiation field than objects with detected CIV emission at $z<2$ and adds to the growing sample of low-mass (log(M/M$_odot)lesssim9$) galaxies at the epoch of reionization with strong radiation fields from star formation.
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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.
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.
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.
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.
[abbreviated] We present a census of Lyalpha emission at $zgtrsim7$ utilizing deep near infrared HST 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 Lyalpha 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 reaches $5times10^{-18}$erg/s/cm$^{2}$ per position angle over the full wavelength range of GLASS (0.8-1.7$mu$m). Based on the conditional probability of Lyalpha emission measured from the ground at $zsim7$ we would have expected 12-18 Lyalpha emitters. This is consistent with the number of detections, within the uncertainties, confirming the drop in Lyalpha emission with respect to $zsim6$. These candidates include a promising source at $z=8.1$. The spatial extent of Lyalpha in a deep stack of the most convincing Lyalpha emitters with $langle zrangle=7.2$ 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 $f_textrm{CIV} / f_textrm{Ly${alpha}$} lesssim 0.32$ and $f_textrm{CIII]} / f_textrm{Ly$alpha$} lesssim 0.23$ in good agreement with other values published in the literature.
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