Discovery of Nine Intermediate Redshift Compact Quiescent Galaxies in the Sloan Digital Sky Survey

Abstract

We identify nine galaxies with dynamical masses of M_dyn>10^10 M_sol as photometric point sources, but with redshifts between z=0.2 and z=0.6, in the Sloan Digital Sky Survey (SDSS) spectro-photometric database. All nine galaxies have archival Hubble Space Telescope (HST) images. Surface brightness profile fitting confirms that all nine galaxies are extremely compact (with circularized half-light radii between 0.4 and 6.6 kpc and the median value of 0.74 kpc) for their velocity dispersion (110<sigma<340 km/s; median sigma=178 km/s). From the SDSS spectra, three systems are dominated by very young stars; the other six are older than ~1 Gyr (two are E+A galaxies). The three young galaxies have disturbed morphologies and the older systems have smooth profiles consistent with a single Sersic function. All nine lie below the z~0 velocity dispersion-half-light radius relation. The most massive system - SDSSJ123657.44+631115.4 - lies right within the locus for massive compact z>1 galaxies and the other eight objects follow the high-redshift dynamical size-mass relation.

Accepted for publication in the Astrophysical Journal Letters