Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z$\gtrsim$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 $2\le z\le 2.5$ with star formation rates of SFR$\sim$100M${}_{\odot }$ y${}^{-1}$ and masses of log(M/M${}_{\odot }$)$\sim 10.8$. Their high integrated gas velocity dispersions of $\ddot{I}{ƒ}_{\mathrm{int}}$=230${}_{-30}^{+40}$ km s${}^{-1}$, as measured from emission lines of H${}_{\hat{I}}\pm$ and [OIII], and the resultant M${}_{\star }-\ddot{I}{ƒ}_{\mathrm{int}}$ relation and M${}_{\star }$$-$M${}_{\mathrm{dyn}}$ all match well to those of compact quiescent galaxies at $z\sim 2$, as measured from stellar absorption lines. Since log(M${}_{\star }$/M${}_{\mathrm{dyn}}$)$=-0.06\pm 0.2$ dex, these compact SFGs appear to be dynamically relaxed and more evolved, i.e., more depleted in gas and dark matter ($<$13${}_{-13}^{+17}$\%) than their non-compact SFG counterparts at the same epoch. Without infusion of external gas, depletion timescales are short, less than $\sim$300 Myr. This discovery adds another link to our new dynamical chain of evidence that compact SFGs at $z\gtrsim 2$ are already losing gas to become the immediate progenitors of compact quiescent galaxies by $z\sim 2$.

12 pages, 7 figures, submitted to ApJ