Early-type galaxies have been the predominant morphological class for massive galaxies since only z ∼ 1

Abstract

Present-day massive galaxies are composed mostly of early-type objects. It is\nunknown whether this was also the case at higher redshifts. In a hierarchical\nassembling scenario the morphological content of the massive population is\nexpected to change with time from disk-like objects in the early Universe to\nspheroid-like galaxies at present. In this paper we have probed this\ntheoretical expectation by compiling a large sample of massive\n(M_{stellar}>10^{11} h_{70}^{-2} M_{Sun}$) galaxies in the redshift interval 0\n< z < 3. Our sample of 1082 objects comprises 207 local galaxies selected from\nSDSS plus 875 objects observed with the HST belonging to the POWIR/DEEP2 and\nGNS surveys. 639 of our objects have spectroscopic redshifts. Our morphological\nclassification is performed as close as possible to the optical restframe\naccording to the photometric bands available in our observations both\nquantitatively (using the Sersic index as a morphological proxy) and\nqualitative (by visual inspection). Using both techniques we find an enormous\nchange on the dominant morphological class with cosmic time. The fraction of\nearly-type galaxies among the massive galaxy population has changed from\n~20-30% at z~3 to ~70% at z=0. Early type galaxies have been the predominant\nmorphological class for massive galaxies since only z~1.\n