THE GRISM LENS-AMPLIFIED SURVEY FROM SPACE (GLASS). I. SURVEY OVERVIEW AND FIRST DATA RELEASE

Abstract

We give an overview of the Grism Lens Amplified Survey from Space (GLASS), a\nlarge Hubble Space Telescope program aimed at obtaining grism spectroscopy of\nthe fields of ten massive clusters of galaxies at redshift z=0.308-0.686,\nincluding the Hubble Frontier Fields (HFF). The Wide Field Camera 3 yields near\ninfrared spectra of the cluster cores, covering the wavelength range\n0.81-1.69mum through grisms G102 and G141, while the Advanced Camera for\nSurveys in parallel mode provides G800L spectra of the infall regions of the\nclusters. The WFC3 spectra are taken at two almost orthogonal position angles\nin order to minimize the effects of confusion. After summarizing the scientific\ndrivers of GLASS, we describe the sample selection as well as the observing\nstrategy and data processing pipeline. We then utilize MACSJ0717.5+3745, a HFF\ncluster and the first one observed by GLASS, to illustrate the data quality and\nthe high-level data products. Each spectrum brighter than H_AB=23 is visually\ninspected by at least two co-authors and a redshift is measured when sufficient\ninformation is present in the spectra. Furthermore, we conducted a thorough\nsearch for emission lines through all the GLASS WFC3 spectra with the aim of\nmeasuring redshifts for sources with continuum fainter than H_AB=23. We provide\na catalog of 139 emission-line based spectroscopic redshifts for extragalactic\nsources, including three new redshifts of multiple image systems (one probable,\ntwo tentative). In addition to the data itself we also release software tools\nthat are helpful to navigate the data.