The FMOS-COSMOS survey of star-forming galaxies at z ~ 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 COSMOS field, using the Fiber Multi-Object Spectrograph on the Subaru telescope, designed to characterize the star-forming galaxy population at $1.4<z<1.7$. The high-resolution mode is implemented to detect H$\hat{I}\pm$ in emission between $1.6-1.8\hat{\mathrm{I}}¼\mathrm{m}$ with $f_{\mathrm{H}\hat{\mathrm{I}}\pm }\gtrsim 4\times 10^{-17}$ erg cm${}^{-2}$ s${}^{-1}$. Here, we specifically focus on 271 sBzK-selected galaxies that yield a H$\hat{I}\pm$ detection thus providing a redshift and emission line luminosity to establish the relation between star formation rate and stellar mass. With further $J$-band spectroscopy for 89 of these, the level of dust extinction is assessed by measuring the Balmer decrement using co-added spectra. We find that the extinction ($0.6\lesssim A_{\mathrm{H}\hat{\mathrm{I}}\pm }\lesssim 2.5$) rises with stellar mass and is elevated at high masses compared to low-redshift galaxies. Using this subset of the spectroscopic sample, we further find that the differential extinction between stellar and nebular emission \hbox{$E_{\mathrm{star}}(B-V)/E_{\mathrm{neb}}(B-V)$} is 0.7--0.8, dissimilar to that typically seen at low redshift. After correcting for extinction, we derive an H$\hat{I}\pm$-based main sequence with a slope ($0.81\pm 0.04$) and normalization similar to previous studies at these redshifts.

6 pages, 4 figures, and 1 table. Published in ApJ Letters