FMOS near-IR spectroscopy of<i>Herschel</i>-selected galaxies: star formation rates, metallicity and dust attenuation at<i>z</i>∼ 1

Abstract

We investigate the properties (e.g. star formation rate, dust attenuation, stellar mass and metallicity) of a sample of infrared (IR) luminous galaxies at z ∼ 1 via near-IR spectroscopy with Subaru-FMOS. Our sample consists of Herschel SPIRE and Spitzer MIPS selected sources in the COSMOS field with photometric redshifts in the range of 0.7 < zphot < 1.8, which have been targeted in two pointings (0.5 deg2) with FMOS. We find a modest success rate for emission-line detections, with candidate Hα emission lines detected for 57 of 168 SPIRE sources (34 per cent). By stacking the near-IR spectra we directly measure the mean Balmer decrement for the Hα and Hβ lines, finding a value of 〈E(B − V)〉 = 0.51 ± 0.27 for 〈LIR〉 = 1012 L⊙ sources at 〈z〉 = 1.36. By comparing star formation rates estimated from the IR and from the dust-uncorrected Hα line we find a strong relationship between dust attenuation and star formation rate. This relation is broadly consistent with that previously seen in star-forming galaxies at z ∼ 0.1. Finally, we investigate the metallicity via the N2 ratio, finding that z ∼ 1 IR-selected sources are indistinguishable from the local mass–metallicity relation. We also find a strong correlation between dust attenuation and metallicity, with the most metal-rich IR sources experiencing the largest levels of dust attenuation.