Superdense massive galaxies in the Nearby Universe

TL;DR

This study investigates the rarity and properties of superdense massive galaxies in the nearby universe, finding they are extremely uncommon, relatively young, and metal-rich, challenging existing size evolution models.

Contribution

The paper provides the first large-scale observational evidence that superdense massive galaxies are exceedingly rare in the local universe and characterizes their properties.

Findings

Only ~0.03% of local galaxies are superdense and massive.

These galaxies are surprisingly young (~2 Gyr) and metal-rich.

Results challenge current size evolution scenarios for massive galaxies.

Abstract

Superdense massive galaxies (r_e~1 kpc; M~10^{11} Msun) 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 SDSS Data Release 6 we find only a tiny fraction of galaxies (~0.03%) with r_e<1.5 kpc and M_*>8x10^{10} Msun in the local Universe (z<0.2). Surprinsingly, 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.