Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z$\gtrsim$2: High velocity dispersions in progenitors of compact quiescent galaxies

TL;DR

This study uses Keck-I MOSFIRE spectroscopy to show that compact star-forming galaxies at z~2 have high velocity dispersions and are likely the progenitors of compact quiescent galaxies, indicating advanced dynamical evolution.

Contribution

It provides the first detailed dynamical analysis of compact SFGs at z~2, linking their properties to those of quiescent galaxies and suggesting rapid gas depletion.

Findings

High gas velocity dispersions (~230 km/s) in compact SFGs.

Compact SFGs have similar dynamical and stellar mass relations as quiescent galaxies.

Short gas depletion timescales (<300 Myr) imply rapid evolution into quiescent galaxies.

Abstract

We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13 compact star-forming galaxies (SFGs) at redshift $2\leq z \leq2.5$ with star formation rates of SFR$\sim$100M$_{\odot}$ y$^{-1}$ and masses of log(M/M$_{\odot}$)$\sim10.8$. Their high integrated gas velocity dispersions of $\sigma_{\rm{int}}$=230$^{+40}_{-30}$ km s$^{-1}$, as measured from emission lines of H$_{\alpha}$ and [OIII], and the resultant M$_{\star}-\sigma_{\rm{int}}$ relation and M$_{\star}$$-$M$_{\rm{dyn}}$ all match well to those of compact quiescent galaxies at $z\sim2$, as measured from stellar absorption lines. Since log(M$_{\star}$/M$_{\rm{dyn}}$)$=-0.06\pm0.2$ dex, these compact SFGs appear to be dynamically relaxed and more evolved, i.e., more depleted in gas and dark matter ($<$13$^{+17}_{-13}$\%) 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 $z\gtrsim2$ are already losing gas to become the immediate progenitors of compact quiescent galaxies by $z\sim2$.