Intrinsic shape variation of quiescent galaxies from redshift 2.5 to 0.5

TL;DR

This study investigates the intrinsic shapes of quiescent galaxies across redshifts 0.5 to 2.5, revealing that higher redshift galaxies are thinner and that massive galaxies are generally thick oblate structures, with minor mergers influencing their evolution.

Contribution

It provides the first comprehensive analysis of intrinsic galaxy shapes across a wide redshift range, linking shape evolution to galaxy formation processes.

Findings

Massive quiescent galaxies are predominantly thick oblate structures.

Galaxies at higher redshift are systematically thinner.

Early-type galaxies at higher redshift are more prolate than at lower redshift.

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.