Pieter G. van Dokkum, Joel Leja, Erica June Nelson, Shannon Patel, Rosalind E. Skelton, Ivelina Momcheva, Gabrial Brammer, Katherine E. Whitaker, Britt Lundgren, Mattia Fumagalli, Charlie Conroy, Natascha Förster Schreiber, Marijn Franx, Mariska Kriek, Ivo Labbé, Danilo Marchesini, Hans-Walter Rix, Arjen van der Wel, Stijn Wuyts
Galaxies with the mass of the Milky Way dominate the stellar mass density of the Universe but it is uncertain how and when they were assembled. Here we study progenitors of these galaxies out to z~2.5, using data from the 3D-HST and CANDELS Treasury surveys. We find that galaxies with present-day stellar masses of log(M)~10.7 M_sun built ~90% of their stellar mass since z~2.5, with most of the star formation occurring before z~1. In marked contrast to the assembly history of massive elliptical galaxies, the centers and outer parts of the galaxies built up at roughly the same rate between z~2.5 and z~1. We therefore conclude that a "standard" model for the formation of spiral galaxies, with the bulge assembling first and the disk building around it, is probably not correct. Instead, bulges (and black holes) likely formed in lockstep with disks, through bar instabilities, clump migration or other processes. We find that after z~1 the growth in the central regions gradually stopped and the disk continued to build, consistent with recent studies of the gas distributions in z~1 galaxies and the properties of many spiral galaxies today.
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http://arxiv.org/abs/1304.2391
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