Superdense massive galaxies in the nearby universe

Abstract

Superdense massive galaxies (re 1 kpc; M 1011M) were common in the early universe (z ≳ 1.5). Within some hierarchical merging scenarios, a non-negligible fraction (1%-10%) of these galaxies is expected to survive since that epoch, retaining their compactness and presenting old stellar populations in the present universe. Using the NYU Value-Added Galaxy Catalog from the Sloan Digital Sky Survey Data Release 6, we find only a tiny fraction of galaxies (0.03%) with re ≲ 1.5 kpc and M ≳ 8 × 1010M in the local universe (z < 0.2). Surprisingly, they are relatively young (2 Gyr) and metal-rich ([Z/H] 0.2). The consequences of these findings within the current two competing size evolution scenarios for the most massive galaxies ("dry" mergers vs. "puffing up" due to quasar activity) are discussed. © 2009. The American Astronomical Society. All rights reserved..