Revealing the Stellar Mass and Dust Distributions of Submillimeter Galaxies at Redshift 2

We combine high-resolution ALMA and HST/CANDELS observations of 20 submillimeter galaxies (SMGs), predominantly from the AS2UDS survey at z ~= 2, with bright rest-frame optical counterparts (Ks <~ 22.9) to investigate the resolved structural properties of their dust and stellar components. We derive two-dimensional stellar-mass distributions that are inferred from spatial mass-to-light ratio (M / L*) corrections based on rest-frame optical colors. Due to the high central column densities of dust in our SMGs, our mass distributions likely represent a lower limit to the true central mass density. The centroid positions between the inferred stellar-mass and the dust distributions agree within 1.1 kpc, indicating an overall good spatial agreement between the two components. The majority of our sources exhibit compact dust configurations relative to the stellar component (with a median ratio of effective radii R(e,dust) / R(e,*) = 0.6). This ratio does not change with specific star formation rate over the factor of 30 spanned by our targets, sampling the locus of “normal” main-sequence galaxies up to the starburst regime, log( sSFR / sSFR(MS)) >= 0.5. Unlike typical spiral galaxies in the local universe, our results imply that massive SMGs are experiencing centrally enhanced star formation. The sizes and stellar densities of our SMGs are in agreement with those of the passive population at z = 1.5, which is consistent with these systems being the descendants of z ~= 2 SMGs