Morphology and structure of extremely red objects at $z\sim1$ in the CANDELS-COSMOS field

TL;DR

This study investigates the structural and morphological differences of extremely red galaxies at z~1 in the CANDELS-COSMOS field, revealing distinct sizes, structures, and evolutionary implications for passive and star-forming types.

Contribution

It provides detailed measurements of sizes and morphologies of EROs at z~1, distinguishing old passive from dusty star-forming galaxies, and suggests different evolutionary pathways.

Findings

OGs are more compact and elliptical-like with higher concentration.

DGs are heterogeneous with bulges, disks, and irregular features.

Minor mergers likely influence OGs' structure, secular evolution affects DGs.

Abstract

Using high-resolution HST/Wide Field Camera 3 F125W imaging from the CANDELS-COSMOS field, we report the the structural and morphological properties of Extremely Red Objects (EROs) at $z\sim1$. Based on the UVJ color criteria, we separate EROs into two types: old passive galaxies (OGs) and dusty star-forming galaxies (DGs). For a given stellar mass, we find that the mean size of OGs (DGs) is smaller by a factor of $\sim2$ (1.5) than that of present-day early-type (late-type) galaxies at rest-frame optical wavelength. We derive the average effective radii of OGs and DGs, corresponding to $2.09\pm1.13$ kpc and $3.27\pm1.14$ kpc, respectively. Generally, The DGs are heterogeneous, with mixed features including bulges, disks, and irregular structures, with relatively high $M_{\rm 20}$, small size and low $G$, while OGs are elliptical-like compact morphologies with lower $M_{\rm 20}$, larger size and higher $G$, indicating the more concentrated and symmetric spatial extent of stellar population distribution in OGs than DGs. The findings imply that OGs and DGs have different evolutionary processes, and the minor merger scenario is the most likely mechanism for the structural properties of OGs. However, the size evolution of DGs is possibly due to the secular evolution of galaxies.