G. Barro, University of California - Santa Cruz
S. M. Faber, University of California - Santa Cruz
P. G. Pérez-González, Universidad Complutense de Madrid, Spain
C. Pacifici, Yonsei University Observatory, South Korea
J. R. Trump, Pennsylvania State University
D. C. Koo, University of California - Santa Cruz
S. Wuyts, Max-Planck-Institut für extraterrestrische Physik, Germany
Y. Guo, University of California - Santa Cruz
E. Bell, University of Michigan
A. Dekel, Hebrew University, Israel
L. Porter, University of California - Santa Cruz
J. Primack, University of California - Santa Cruz
H. Ferguson, Space Telescope Science Institute
M. L. N. Ashby, Harvard-Smithsonian Center for Astrophysics
K. Caputi, University of Groningen, Netherlands
D. Ceverino, Universidad Autónoma de Madrid, Spain
D. Croton, Swinburne University of Technology, Australia
G. G. Fazio, Harvard-Smithsonian Center for Astrophysics
M. Giavalisco, University of Massachusetts
L. Hsu, Max-Planck-Institut für extraterrestrische Physik, Germany
Dalibor D. Kocevski, University of KentuckyFollow
A. Koekemoer, Space Telescope Science Institute
P. Kurcynski, Rutgers University
P. Kollipara, University of California - Santa Cruz
J. Lee, Yonsei University Observatory, South Korea
D. H. McIntosh, University of Missouri - Kansas City
E. McGrath, Colby College
C. Moody, University of California - Santa Cruz
R. Somerville, Rutgers University
C. Papovich, Texas A&M University
M. Salvato, Max-Planck-Institut für extraterrestrische Physik, Germany
P. Santini, INAF-Osservatorio Astronomico di Roma, Italy
T. Tal, University of California - Santa Cruz
A. van der Wel, Max-Planck-Institut für Astronomie, Germany
C. C. Williams, University of Massachusetts
S. P. Willner, Harvard-Smithsonian Center for Astrophysics
A. Zolotov, Hebrew University, Israel


We analyze the star-forming and structural properties of 45 massive (log(M/M ) >10) compact star-forming galaxies (SFGs) at 2 < z < 3 to explore whether they are progenitors of compact quiescent galaxies at z ~ 2. The optical/NIR and far-IR Spitzer/Herschel colors indicate that most compact SFGs are heavily obscured. Nearly half (47%) host an X-ray-bright active galactic nucleus (AGN). In contrast, only about 10% of other massive galaxies at that time host AGNs. Compact SFGs have centrally concentrated light profiles and spheroidal morphologies similar to quiescent galaxies and are thus strikingly different from other SFGs, which typically are disk-like and sometimes clumpy or irregular. Most compact SFGs lie either within the star formation rate (SFR)-mass main sequence (65%) or below it (30%), on the expected evolutionary path toward quiescent galaxies. These results show conclusively that galaxies become more compact before they lose their gas and dust, quenching star formation. Using extensive HST photometry from CANDELS and grism spectroscopy from the 3D-HST survey, we model their stellar populations with either exponentially declining (τ) star formation histories (SFHs) or physically motivated SFHs drawn from semianalytic models (SAMs). SAMs predict longer formation timescales and older ages ~2 Gyr, which are nearly twice as old as the estimates of the τ models. Both models yield good spectral energy distribution fits, indicating that the systematic uncertainty in the age due to degeneracies in the SFH is of that order of magnitude. However, SAM SFHs better match the observed slope and zero point of the SFR-mass main sequence. Contrary to expectations, some low-mass compact SFGs (log(M/M ) =10-10.6) have younger ages but lower specific SFRs than that of more massive galaxies, suggesting that the low-mass galaxies reach the red sequence faster. If the progenitors of compact SFGs are extended SFGs, state-of-the-art SAMs show that mergers and disk instabilities (DIs) are both able to shrink galaxies, but DIs are more frequent (60% versus 40%) and form more concentrated galaxies. We confirm this result via high-resolution hydrodynamic simulations.

Document Type


Publication Date


Notes/Citation Information

Published in The Astrophysical Journal, v. 791, no. 1, article 52, p. 1-23.

© 2014. The American Astronomical Society. All rights reserved.

Reproduced by permission of the AAS.

Digital Object Identifier (DOI)

Funding Information

Support for Program number HST-GO-12060 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. G.B. acknowledges support from NSF grant AST-08-08133. P.G.P.-G. acknowledges support from grant AYA2012-31277-E. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM), partnered with the University of California Observatories at Santa Cruz (UCO/Lick, UCSC). C.P. acknowledges the support by the KASI-Yonsei Joint Research Program for the Frontiers of Astronomy and Space Science funded by the Korea Astronomy and Space Science Institute. J.L. acknowledges the support by the National Research Foundation of Korea through the SRC grant to the Center for Galaxy Evolution Research and the Doyak grant (No. 20090078756).

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