An ALMA Survey of Submillimeter Galaxies in the Extended Chandra Deep Field South: Near-infrared morphologies and stellar sizes

Abstract

We analyse HST WFC3/$H_{160}$-band observations of a sample of 48 ALMA-detected submillimeter galaxies (SMGs) in the Extended Chandra Deep Field South field, to study their stellar morphologies and sizes. We detect 79$\pm$17% of the SMGs in the $H_{160}$-band imaging with a median sensitivity of 27.8 mag, and most (80%) of the non-detections are SMGs with 870$\hat{I}¼$m fluxes of $S_{870}<$3 mJy. With a surface brightness limit of $\hat{I}{¼}_H\sim$26 mag arcsec${}^{-2}$, we find that 82$\pm$9% of the $H_{160}$-band detected SMGs at $z=$ 1-3 appear to have disturbed morphologies, meaning they are visually classified as either irregulars or interacting systems, or both. By determining a Sérsic fit to the $H_{160}$ surface-brightness profiles we derive a median Sérsic index of $n=$1.2$\pm$0.3 and a median half-light radius of $r_e=$4.4${}_{-0.5}^{+1.1}$ kpc for our SMGs at $z=$1-3. We also find significant displacements between the positions of the $H_{160}$-component and 870$\hat{I}¼$m emission in these systems, suggesting that the dusty star-burst regions and less-obscured stellar distribution are not co-located. We find significant differences in the sizes and the Sérsic index between our $z=$2-3 SMGs and $z\sim$2 quiescent galaxies, suggesting a major transformation of the stellar light profile is needed in the quenching processes if SMGs are progenitors of the red-and-dead $z\sim$2 galaxies. Given the short-lived nature of SMGs, we postulate that the majority of the $z=$2-3 SMGs with $S_{870}\gtrsim$2 mJy are early/mid-stage major mergers.

ApJ in press, 32 pages, 13 figures