Implications Of Increased Central Mass Surface Densities For The Quenching Of Low-Mass Galaxies

We use the Cosmic Assembly Deep Near-infrared Extragalactic Legacy Survey data to study the relationship between quenching and the stellar mass surface density within the central radius of 1 kpc (sigma(1)) of low-mass galaxies (stellar mass M (*) less than or similar to 10(9.5) M (circle dot)) at 0.5 <= z < 1.5. Our sample is mass complete down to similar to 10(9) M (circle dot) at 0.5 <= z < 1.0. We compare the mean sigma(1) of star-forming galaxies (SFGs) and quenched galaxies (QGs) at the same redshift and M (*). We find that low-mass QGs have a higher sigma(1) than low-mass SFGs, similar to galaxies above 10(10) M (circle dot). The difference of sigma(1) between QGs and SFGs increases slightly with M (*) at M (*) less than or similar to 10(10) M (circle dot) and decreases with M (*) at M (*) greater than or similar to 10(10) M (circle dot). The turnover mass is consistent with the mass where quenching mechanisms transition from internal to environmental quenching. At 0.5 <= z < 1.0, we find that sigma(1) of galaxies increases by about 0.25 dex in the green valley (i.e., the transition region from star forming to fully quenched), regardless of their M (*). Using the observed specific star formation rate gradient in the literature as a constraint, we estimate that the quenching timescale (i.e., time spent in the transition) of low-mass galaxies is a few (similar to 4) Gyr at 0.5 <= z < 1.0. The mechanisms responsible for quenching need to gradually quench star formation in an outside-in way, i.e., preferentially ceasing star formation in outskirts of galaxies while maintaining their central star formation to increase sigma(1). An interesting and intriguing result is the similarity of the growth of sigma(1) in the green valley between low-mass and massive galaxies, which suggests that the role of internal processes in quenching low-mass galaxies is a question worthy of further investigation.