THE FMOS-COSMOS SURVEY OF STAR-FORMING GALAXIES AT <i>z</i> ∼ 1.6. I. Hα-BASED STAR FORMATION RATES AND DUST EXTINCTION

Abstract

We present the first results from a near-IR spectroscopic survey of the\nCOSMOS field, using the Fiber Multi-Object Spectrograph on the Subaru\ntelescope, designed to characterize the star-forming galaxy population at\n$1.4&lt;z&lt;1.7$. The high-resolution mode is implemented to detect H$\\alpha$ in\nemission between $1.6{\\rm -}1.8 \\mathrm{\\mu m}$ with $f_{\\rm\nH\\alpha}\\gtrsim4\\times10^{-17}$ erg cm$^{-2}$ s$^{-1}$. Here, we specifically\nfocus on 271 sBzK-selected galaxies that yield a H$\\alpha$ detection thus\nproviding a redshift and emission line luminosity to establish the relation\nbetween star formation rate and stellar mass. With further $J$-band\nspectroscopy for 89 of these, the level of dust extinction is assessed by\nmeasuring the Balmer decrement using co-added spectra. We find that the\nextinction ($0.6\\lesssim A_\\mathrm{H\\alpha} \\lesssim 2.5$) rises with stellar\nmass and is elevated at high masses compared to low-redshift galaxies. Using\nthis subset of the spectroscopic sample, we further find that the differential\nextinction between stellar and nebular emission\n\\hbox{$E_\\mathrm{star}(B-V)/E_\\mathrm{neb}(B-V)$} is 0.7--0.8, dissimilar to\nthat typically seen at low redshift. After correcting for extinction, we derive\nan H$\\alpha$-based main sequence with a slope ($0.81\\pm0.04$) and normalization\nsimilar to previous studies at these redshifts.\n