SPT 0538–50: PHYSICAL CONDITIONS IN THE INTERSTELLAR MEDIUM OF A STRONGLY LENSED DUSTY STAR-FORMING GALAXY AT<i>z</i>= 2.8

Abstract

We present observations of SPT-S J053816-5030.8, a gravitationally-lensed\ndusty star forming galaxy (DSFG) at z = 2.7817, first discovered at millimeter\nwavelengths by the South Pole Telescope. SPT 0538-50 is typical of the\nbrightest sources found by wide-field millimeter-wavelength surveys, being\nlensed by an intervening galaxy at moderate redshift (in this instance, at z =\n0.441). We present a wide array of multi-wavelength spectroscopic and\nphotometric data on SPT 0538-50, including data from ALMA, Herschel PACS and\nSPIRE, Hubble, Spitzer, VLT, ATCA, APEX, and the SMA. We use high resolution\nimaging from HST to de-blend SPT 0538-50, separating DSFG emission from that of\nthe foreground lens. Combined with a source model derived from ALMA imaging\n(which suggests a magnification factor of 21 +/- 4), we derive the intrinsic\nproperties of SPT 0538-50, including the stellar mass, far-IR luminosity, star\nformation rate, molecular gas mass, and - using molecular line fluxes - the\nexcitation conditions within the ISM. The derived physical properties argue\nthat we are witnessing compact, merger-driven star formation in SPT 0538-50,\nsimilar to local starburst galaxies, and unlike that seen in some other DSFGs\nat this epoch.\n