Hα Observations of a Large Sample of Galaxies atz∼ 2: Implications for Star Formation in High‐Redshift Galaxies

Using H-alpha spectra of 114 rest-frame UV-selected galaxies at z~2, wecompare inferred star formation rates (SFRs) with those determined from the UVcontinuum luminosity. After correcting for extinction using standard techniquesbased on the UV continuum slope, we find excellent agreement between theindicators, with = 31 Msun/yr and = 29 Msun/yr. The agreementbetween the indicators suggests that the UV luminosity is attenuated by antypical factor of ~4.5 (with a range from no attenuation to a factor of ~100for the most obscured object in the sample), in good agreement with estimatesof obscuration from X-ray, radio and mid-IR data. The H-alpha luminosity isattenuated by a factor of ~1.7 on average, and the maximum H-alpha attenuationis a factor of ~5. In agreement with X-ray and mid-IR studies, we find that theSFR increases with increasing stellar mass and at brighter K magnitudes, to ~ 60 Msun/yr for galaxies with K<20; the correlation between Kmagnitude and SFR is much stronger than the correlation between stellar massand SFR. All galaxies in the sample have SFRs per unit area Sigma_SFR in therange observed in local starbursts. We compare the instantaneous SFRs and thepast average SFRs as inferred from the ages and stellar masses, finding thatfor most of the sample, the current SFR is an adequate representation of thepast average. There is some evidence that the most massive galaxies (M_star>10^11 Msun) have had higher SFRs in the past.Comment: 14 pages, 7 figures, 1 table. Accepted for publication in Ap