Expected number of massive galaxy relics in the present day universe

Abstract

The number of present day massive galaxies that have survived untouched since their formation at high-z is an important observational constraint to the hierarchical galaxy formation models. Using three different semianalytical models based on the Millenium simulation, we quantify the expected fraction and number densities of the massive galaxies that form at z > 2 and have evolved in stellar mass less than 10% and 30%. We find that only a small fraction of the massive galaxies that already formed at z ∼ 2 have remained almost unaltered since their formation (<2% with δM */M * < 0.1 and <8% with δM */M * < 0.3). These fractions correspond to the following number densities of massive relics in the present day universe: ∼1.2 × 10-6 Mpc-3 for δM */M * < 0.1 and ∼5.7 × 10-6 Mpc -3 for δM */M * < 0.3. The observed number of relic candidates found in the nearby universe is rather uncertain today (with uncertainties up to a factor of ∼100), preventing us from establishing firm conclusions about the ability of current theoretical expectations to predict such an important number. © 2013. The American Astronomical Society. All rights reserved.