FMOS near-IR spectroscopy of Herschel selected galaxies: star formation
  rates, metallicity and dust attenuation at z~1
  We investigate the properties (e.g. star formation rate, dust attentuation,
stellar mass and metallicity) of a sample of infrared luminous galaxies at z
\sim 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 0.7 < z-phot < 1.8, which have been targeted
in 2 pointings (0.5 sq. deg.) with FMOS. We find a modest success rate for
emission line detections, with candidate H{\alpha} 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 H{\alpha} and H{\beta}
lines, finding a value of <E(B-V)> = 0.51\pm0.27 for <LIR> = 10^12 Lsol sources
at <z> = 1.36. By comparing star formation rates estimated from the IR and from
the dust uncorrected H{\alpha} 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 attentuation and metallicity, with the
most metal-rich IR-sources experiencing the largest levels of dust attenuation.
