COMPACT QUIESCENT GALAXIES AT INTERMEDIATE REDSHIFTS,

Abstract

From several searches of the area common to the Sloan Digital Sky Survey and the United Kingdom Infrared Telescope Infrared Deep Sky Survey, we have selected 22 luminous galaxies between $z \sim$ 0.4 and $z \sim$ 0.9 that have colors and sizes similar to those of the compact quiescent galaxies at $z>2$. By exploring structural parameters and stellar populations, we found that most of these galaxies actually formed most of their stars at $z<2$ and are generally less compact than those found at $z > 2$. Several of these young objects are disk-like or possibly prolate. This lines up with several previous studies which found that massive quiescent galaxies at high redshifts often have disk-like morphologies. If these galaxies were to be confirmed to be disk-like, their formation mechanism must be able to account for both compactness and disks. On the other hand, if these galaxies were to be confirmed to be prolate, the fact that prolate galaxies do not exist in the local universe would indicate that galaxy formation mechanisms have evolved over cosmic time. We also found five galaxies forming over 80% of their stellar masses at $z>2$. Three of these galaxies appear to have been modified to have spheroid-like morphologies, in agreement with the scenario of "inside-out" buildup of massive galaxies. The remaining galaxies, SDSS\,J014355.21+133451.4 and SDSS\,J115836.93+021535.1, have truly old stellar populations and disk-like morphologies. These two objects would be good candidates for nearly unmodified compact quiescent galaxies from high redshifts that are worth future study.