INVESTIGATING Hα, UV, AND IR STAR-FORMATION RATE DIAGNOSTICS FOR A LARGE SAMPLE OF z ∼ 2 GALAXIES

We use a sample of 262 spectroscopically confirmed star-forming galaxies at redshifts 2.08 <= z <= 2.51 to compare Ha, ultraviolet (UV), and IR star formation rate (SFR) diagnostics and to investigate the dust properties of the galaxies. At these redshifts, the H alpha line shifts to the K-s band. By comparing K-s-band photometry to underlying stellar population model fits to other UV, optical, and near-infrared data, we infer the H alpha flux for each galaxy. We obtain the best agreement between H alpha- and UV-based SFRs if we assume that the ionized gas and stellar continuum are reddened by the same value and that the Calzetti attenuation curve is applied to both. Aided with MIPS 24 mu m data, we find that an attenuation curve steeper than the Calzetti curve is needed to reproduce the observed IR/UV ratios of galaxies younger than 100 Myr. Furthermore, using the bolometric SFR inferred from the UV and mid-IR data (SFRIR+SFRUV), we calculated the conversion between the H alpha luminosity and SFR to be (7.5 +/- 1.3) x 10(-42) for a Salpeter initial mass function, which is consistent with the Kennicutt conversion. The derived conversion factor is independent of any assumption of the dust correction and is robust to stellar population model uncertainties.