Intrinsic shape variation of quiescent galaxies from redshift 2.5 to 0.5

Abstract

According to the standard inside-out galaxy formation scenario, galaxies first form a dense core and then gradually assemble their outskirts. This implies that galaxies with similar central stellar mass densities might have evolutionary links. We use the UVJ color-color diagram to select quiescent galaxies in the redshift interval from 0.5 to 2.5 and classify them into different subsamples based on their central stellar mass densities, stellar mass, morphological type and redshift. We then infer the intrinsic axis ratios $\mu_{B/A}$ and $\mu_{C/A}$ of different subsamples based on the apparent axis ratio $q$ distributions, where A, B, and C refers to, respectively, the major, intermediate and minor axis of a triaxial ellipsoidal model. We find that 1) massive quiescent galaxies have typical intrinsic shapes similarly close to thick oblate structures, with $\mu_{B/A} \gtrsim 0.9$, regardless of stellar mass, redshift, or central stellar mass densities, and 2) galaxies at higher redshift are systematically thinner than their lower-redshift counterparts, and 3) when splitting the sample into early type and late type with Sersic indices, ETGs at higher redshift are slightly more prolate (smaller average $\mu_{B/A}$) than those at lower redshift. Minor mergers of galaxies may have played important roles in the structural evolution of quiescent galaxies found in this work.