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 >~ 10¹⁰ M _⊙ 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 images. Surface brightness profile fitting confirms that all nine galaxies are extremely compact (0.4 < R _{e, c} < 6.6 kpc with the median R _{e, c} = 0.74 kpc) for their velocity dispersion (110 < σ < 340 km s^-1 median σ = 178 km s^-1). 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-Sérsic 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.