Galaxy Sizes Since z=2 from the Perspective of Stellar Mass Distribution within Galaxies

How stellar mass assembles within galaxies is still an open question. We present measurements of the stellar mass distribution on kiloparsec-scales for similar to 5500 galaxies with stellar masses above log(M*/M-circle dot) >= 9.8 up to redshift 2.0. We create stellar mass maps from Hubble Space Telescope observations by means of the pixel-by-pixel spectral energy distribution fitting method. These maps are used to derive radii encompassing 20%, 50%, and 80% (r(20), r(50), and r(80)) of the total stellar mass from the best-fit Sersic models. The reliability and limitations of the structural parameter measurements are checked extensively using a large sample (similar to 3000) of simulated galaxies. The size-mass relations and redshift evolution of r(20), r(50), and r(80) are explored for star-forming and quiescent galaxies. At fixed mass, the star-forming galaxies do not show significant changes in their r(20), r(50), and r(80) sizes, indicating self-similar growth. Only above the pivot stellar mass of log(M*/M-circle dot) similar or equal to 10.5 does r(80) evolve as r(80) proportional to (1 + z)(-0.85 +/- 0.20), indicating that mass builds up in the outskirts of these systems (inside-out growth). The Sersic values also increase for the massive star-forming galaxies toward late cosmic time. Massive quiescent galaxies show stronger size evolution at all radii, in particular, the r(20) sizes. For these massive galaxies, Sersic values remain almost constant since at least z similar to 1.3, indicating that the strong size evolution is related to the changes in the outer parts of these galaxies. We make all the structural parameters publicly available.