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Superdense massive galaxies (rₑ~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 rₑ8x10^10 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.
Trujillo et al. (Fri,) studied this question.
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