SIMBAD references

Superdense massive galaxies (r_e∼ 1 kpc; M ∼ 10¹¹ M_{x2609}) 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 r_e≲ 1.5 kpc and M_{sstarf} ≳ 8x10¹⁰ M_{x2609} 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.