The Hubble Space Telescope ACS Grism Parallel Survey. II. First Results and a Catalog of Faint Emission-Line Galaxies at z ≤ 1.6

Abstract

We present the first results from the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Grism Parallel Survey, a large program obtaining deep, slitless ACS grism spectroscopy of high-latitude HST parallel fields. We report on 11 high Galactic latitude fields here, each with grism integration times of more than 12 ks. We identify 601 compact emission-line galaxies at z ~5×10-18 ergs cm-2 s-1 (3 σ). We determine redshifts by cross-correlation of the target spectra with template spectra, followed by visual inspection. We measure star formation rates from the observed [O II] λ3727, [O III] λ5007, and Hα line fluxes. Follow-up observations with the Keck telescope of one of the survey fields confirms our classification and redshifts with σ(z)~=0.02. This is one of the deepest emission-line surveys to date, covering a total area of 121 arcmin2. The rough estimate of the comoving number density of emission-line galaxies in our survey at 0.3