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 \mu m fluxes of S _ { 870 } < 3 mJy .
With a surface brightness limit of \mu _ { 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 ^ { +1.1 } _ { -0.5 } kpc for our SMGs at z = 1–3 .
We also find significant displacements between the positions of the H _ { 160 } -component and 870 \mu 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 .