Guillermo Barro, S. M. Faber, Pablo G. Perez-Gonzalez, David C. Koo, Christina C. Williams, Dale D. Kocevski, Jonathan R. Trump, Mark Mozena, Elizabeth McGrath, Arjen van der Wel, Stijn Wuyts, Eric F. Bell, Darren J. Croton, Avishai Dekel, M. L. N. Ashby, Henry C. Ferguson, Adriano Fontana, Mauro Giavalisco, Norman A. Grogin, Yicheng Guo, Nimish P. Hathi, Philip F. Hopkins, Kuang-Han Huang, Anton M. Koekemoer, Jeyhan S. Kartaltepe, Kyoung-Soo Lee, Jeffrey A. Newman, Lauren A. Porter, Joel R. Primack, Russell E. Ryan, David Rosario, Rachel S. Somerville
We combine high-resolution HST/WFC3 images with multi-wavelength photometry to track the evolution of structure and activity of massive (log(M*) > 10) galaxies at redshifts z = 1.4 - 3 in two fields of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We detect compact, star-forming galaxies (cSFGs) whose number densities, masses, sizes, and star formation rates qualify them as likely progenitors of compact, quiescent, massive galaxies (cQGs) at z = 1.5 - 3. At z > 2 most cSFGs have specific star-formation rates (sSFR = 10^-9 yr^-1) half that of typical, massive SFGs at the same epoch, and host X-ray luminous AGN 30 times (~30%) more frequently. These properties suggest that cSFGs are formed by gas-rich processes (mergers or disk-instabilities) that induce a compact starburst and feed an AGN, which, in turn, quench the star formation on dynamical timescales (few 10^8 yr). The cSFGs are continuously being formed at z = 2 - 3 and fade to cQGs by z = 1.5. After this epoch, cSFGs are rare, thereby truncating the formation of new cQGs. Meanwhile, down to z = 1, existing cQGs continue to enlarge to match local QGs in size, while less-gas-rich mergers and other secular mechanisms shepherd (larger) SFGs as later arrivals to the red sequence. In summary, we propose two evolutionary scenarios of QG formation: an early (z > 2), fast-formation path of rapidly-quenched cSFGs that evolve into cQGs that later enlarge within the quiescent phase, and a slow, late-arrival (z < 2) path for SFGs to form QGs without passing through a compact state.
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http://arxiv.org/abs/1206.5000
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