Imaging of Three Possible Low Redshift Analogs to High Redshift Compact Red Galaxies

TL;DR

This study investigates three low-redshift compact galaxies as analogs to high-redshift massive red galaxies, revealing faint outer structures and young stellar populations, suggesting size evolution occurs through minor mergers over a few billion years.

Contribution

It provides high-resolution imaging evidence of outer structures in low-redshift analogs, supporting the idea that size growth is driven by minor mergers rather than major stochastic events.

Findings

Presence of faint outer structures in all three galaxies

Young stellar populations (~2-4 Gyr) consistent with recent accretion

Outer structures likely formed through minor mergers

Abstract

As part of a larger program to identify and characterize possible low-redshift analogs to massive compact red galaxies found at high redshift, we have examined the morphologies of three low-redshift compact galaxies drawn from the sample of Trujillo et al. (2009). Using deeper and higher resolution images, we have found faint and relatively extensive outer structures in addition to the compact cores identified in the earlier measurements. One object appears to have a small companion that may be involved in an ongoing minor merger of the sort that could be responsible for building up the outer parts of these galaxies. The ages of the dominant stellar populations in these objects are found to be around 2--4 Gyr, in good agreement with the previous estimates. The presence of diffuse outer structures in these galaxies indicates that truly compact and massive red galaxies are exceedingly rare at low redshift. The relatively young stellar populations suggest that the accretion of the extensive outer material must occur essentially universally on relatively short timescales of few billion years or less. These results confirm and extend previous suggestions that the driving mechanism behind the size evolution of high redshift compact galaxies cannot be highly stochastic processes such as major mergers, which would inevitably leave a non-negligible fraction of survivors at low redshift.