Keck-I mosfire spectroscopy of compact star-forming galaxies at z ≳ 2: High velocity dispersions in progenitors of compact quiescent galaxies

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 σ_int km s^-1, as measured from emission lines of Hα and [O III], and the resultant M _∗-σ_int relation and M _&sstarf;-Mdyn 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%), and present larger σ_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.