The Gemini Deep Deep Survey. II. Metals in Star‐forming Galaxies at Redshift 1.3 < z < 2

Abstract

The goal of the Gemini Deep Deep Survey (GDDS) is to study an unbiased sample of K 1.3. The selected objects have colors typical of irregular and Sbc galaxies. Strong [O II] emission indicates high star formation activity in the H II regions (star formation rate ~13-106 M☉ yr-1). The high signal-to-noise ratio composite spectrum shows strong ISM Mg II and Fe II absorption, together with weak Mn II and Mg I lines. The Fe II column density, derived using the curve of growth analysis, is log N = 15.54. This is considerably larger than typical values found in damped Lyα systems (DLAs) along QSO sight lines, where only 10 of 87 (~11%) have log N ≥ 15.2. High Fe II column densities are observed in the z = 2.72 Lyman break galaxy cB58 (log N 15.25) and in gamma-ray burst host galaxies (log N ~ 14.8-15.9). Given our measured Fe II column density and assuming a moderate iron dust depletion (δFe ~ 1 dex), we derive an optical dust extinction of AV ~ 0.6. If the H I column density is log N 0.2. The high completeness of the GDDS sample implies that these results are typical of star-forming galaxies in the 1 < z < 2 redshift range, an epoch that has heretofore been particularly challenging for observational programs.