KECK-I MOSFIRE SPECTROSCOPY OF COMPACT STAR-FORMING GALAXIES AT<i>z</i>≳ 2: HIGH VELOCITY DISPERSIONS IN PROGENITORS OF COMPACT QUIESCENT GALAXIES

Abstract

We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13 compact star-forming galaxies (SFGs) at redshift 2 z 2.5 with star formation rates of SFR 100 M yr -1 and masses of log(M/M ) 10.8. Their high integrated gas velocity dispersions of int = 230 +40 -30 km s -1 , as measured from emission lines of H and [O iii], and the resultant M - int relation and M -M dyn all match well to those of compact quiescent galaxies at z 2, as measured from stellar absorption lines. Since log(M /M dyn ) = -0.06 0.2 dex, these compact SFGs appear to be dynamically relaxed and evolved, i.e., depleted in gas and dark matter (<13 +17 -13 %), and present larger int than their non-compact SFG counterparts at the same epoch. Without infusion of external gas, depletion timescales are short, less than 300 Myr. This discovery adds another link to our new dynamical chain of evidence that compact SFGs at z 2 are already losing gas to become the immediate progenitors of compact quiescent galaxies by z 2.