Physical properties of compact star-forming galaxies at $z\sim2-3$

Abstract

We present a study on the physical properties of compact star-forming galaxies (cSFGs) with $M_{*}\geq10^{10}M_{\odot}$ and $2\leq z\leq3$ in the COSMOS and GOODS-S fields. We find that massive cSFGs have a comoving number density of $(1.0\pm0.1)\times10^{-4}~{\rm Mpc}^{-3}$. The cSFGs are distributed at nearly the same locus on the main sequence as extended star-forming galaxies (eSFGs) and dominate the high-mass end. On the rest-frame $U-V$ vs. $V-J$ and $U-B$ vs. $M_{\rm B}$ diagrams, cSFGs are mainly distributed at the middle of eSFGs and compact quiescent galaxies (cQGs) in all colors, but are more inclined to "red sequence" than "green valley" galaxies. We also find that cSFGs have distributions similar to cQGs on the nonparametric morphology diagrams. The cQGs and cSFGs have larger $Gini$ and smaller $M_{20}$, while eSFGs have the reverse. About one-third of cSFGs show signatures of postmergers, and almost none of them can be recognized as disks. Moreover, those visually extended cSFGs all have lower $Gini$ coefficients ($Gini<0.4$), indicating that the $Gini$ coefficient could be used to clean out noncompact galaxies in a sample of candidate cSFGs. The X-ray-detected counterparts are more frequent among cSFGs than that in eSFGs and cQGs, implying that cSFGs have previously experienced violent gas-rich interactions(such as major mergers or disk instabilities), which could trigger both star formation and black hole growth in an active phase.