Color Gradients and Half-mass Radii of Galaxies Out to z = 2 in the CANDELS/3D-HST Fields: Further Evidence for Important Differences in the Evolution of Mass-weighted and Light-weighted Sizes
Tim B. Miller, Pieter van Dokkum, Lamiya Mowla
Abstract
Abstract Recent studies have indicated that the ratio between half-mass and half-light radii, r mass / r light , varies significantly as a function of stellar mass and redshift, complicating the interpretation of the ubiquitous r light − M * relation. To investigate, in this study we construct the light and color profiles of ∼3000 galaxies at 1 < z < 2 with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo>></mml:mo> <mml:mn>10.25</mml:mn> </mml:math> using imcascade , a Bayesian implementation of the Multi-Gaussian Expansion (MGE) technique. imcascade flexibly represents galaxy profiles using a series of Gaussians, free of any a priori parameterization. We find that both star-forming and quiescent galaxies have, on average, negative color gradients. For star-forming galaxies, we find steeper gradients that evolve with redshift and correlate with dust content. Using the color gradients as a proxy for gradients in the M / L ratio, we measure half-mass radii for our sample of galaxies. There is significant scatter in individual r mass / r light ratios, which is correlated with variation in the color gradients. We find that the median r mass / r light ratio evolves from 0.75 at z = 2 to 0.5 at z = 1, consistent with previous results. We characterize the r mass − M * relation, and we find that it has a shallower slope and shows less redshift evolution than the r light − M * relation. This applies both to star-forming and quiescent galaxies. We discuss some of the implications of using r mass instead of r light , including an investigation of the size−inclination bias and a comparison to numerical simulations.