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 ∼5500 galaxies with stellar masses above $\mathrm{log}({M}_{* }/{M}_{\odot })\geqslant 9.8$ 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% (r₂₀, r₅₀, and r₈₀) of the total stellar mass from the best-fit Sérsic models. The reliability and limitations of the structural parameter measurements are checked extensively using a large sample (∼3000) of simulated galaxies. The size-mass relations and redshift evolution of r₂₀, r₅₀, and r₈₀ are explored for star-forming and quiescent galaxies. At fixed mass, the star-forming galaxies do not show significant changes in their r₂₀, r₅₀, and r₈₀ sizes, indicating self-similar growth. Only above the pivot stellar mass of $\mathrm{log}({M}_{* }/{M}_{\odot })\simeq 10.5$ does r₈₀ evolve as r₈₀ ∝ (1 + z)^-0.85±0.20, indicating that mass builds up in the outskirts of these systems (inside-out growth). The Sérsic 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 r₂₀ sizes. For these massive galaxies, Sérsic values remain almost constant since at least z ∼ 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.