Shards: a global view of the star formation activity at z ~ 0.84 and z ~ 1.23

Abstract

In this paper, we present a comprehensive analysis of star-forming galaxies (SFGs) at intermediate redshifts (z ~ 1). We combine the ultra-deep optical spectro-photometric data from the Survey for High-z Absorption Red and Dead Sources (SHARDS) with deep UV-to-FIR observations in the GOODS-N field. Exploiting two of the 25 SHARDS medium-band filters, F687W17 and F823W17, we select [O II] emission line galaxies at z ~ 0.84 and z ~ 1.23 and characterize their physical properties. Their rest-frame equivalent widths (EWrf([O ii])), line fluxes, luminosities, star formation rates (SFRs), and dust attenuation properties are investigated. The evolution of EW_rf([O II]) closely follows the SFR density evolution of the universe, with a trend of EW_rf([O II]) ∞ (1 + z)^3 up to redshift z ≃1, followed by a possible flattening. The SF properties of the galaxies selected on the basis of their [O II] emission are compared with complementary samples of SFGs selected by their MIR and FIR emission, and also with a general mass-selected sample of galaxies at the same redshifts. We demonstrate observationally that the UVJ diagram (or, similarly, a cut in the specific SFR) is only partially able to distinguish the quiescent galaxies from the SFGs. The SFR–M_* relation is investigated for the different samples, yielding a logarithmic slope ~1, in good agreement with previous results. The dust attenuations derived from different SFR indicators (UV(1600), UV(2800), [O II], IR) are compared and show clear trends with respect to both the stellar mass and total SFR, with more massive and highly star-forming galaxies being affected by stronger dust attenuation.