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Published April 20, 2017 | Submitted + Published
Journal Article Open

Constraints on Quenching of Z ≲ 2 Massive Galaxies from the Evolution of the Average Sizes of Star-forming and Quenched Populations in COSMOS


We use >9400 log(m/M☉) > 10 quiescent and star-forming galaxies at z ≾ 2 in COSMOS/UltraVISTA to study the average size evolution of these systems, with focus on the rare ultra-massive population at log(m/M_☉) > 11.4. The large 2 square degree survey area delivers a sample of ~400 such ultra-massive systems. Accurate sizes are derived using a calibration based on high-resolution images from the Hubble Space Telescope. We find that at these very high masses, the size evolution of star-forming and quiescent galaxies is almost indistinguishable in terms of normalization and power-law slope. We use this result to investigate possible pathways of quenching massive m > M^* galaxies at z < 2. We consistently model the size evolution of quiescent galaxies from the star-forming population by assuming different simple models for the suppression of star formation. These models include an instantaneous and delayed quenching without altering the structure of galaxies and a central starburst followed by compaction. We find that instantaneous quenching reproduces the observed mass-size relation of massive galaxies at z > 1 well. Our starburst+compaction model followed by individual growth of the galaxies by minor mergers is preferred over other models without structural change for log(m/M_☉) > 11.0 galaxies at z > 0.5. None of our models is able to meet the observations at m > M^* and z < 1 without significant contribution of post-quenching growth of individual galaxies via mergers. We conclude that quenching is a fast process in galaxies with m ≥ 10^(11) M_ ⊙, and that major mergers likely play a major role in the final steps of their evolution.

Additional Information

© 2017 American Astronomical Society. Received 2016 July 15. Accepted 2017 March 23. Published 2017 April 17. We would like to thank Dan Masters, Charles Steinhardt, Behnam Darvish, and Bahram Mobasher for valuable discussions. Furthermore, we would like to thank the referee for valuable feedback that greatly improved this manuscript. A.F. acknowledges support from the Swiss National Science Foundation. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under ESO programme ID 179.A-2005 and on data products produced by TERAPIX and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. This work is based on observations taken by the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

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Published - Constraints_on_Quenching_of_Z ≲ 2_Massi...ing_and_Quenched_Populations_in_COSMOS.pdf

Submitted - 1703.09234.pdf


Constraints_on_Quenching_of_Z ≲ 2_Massi...ing_and_Quenched_Populations_in_COSMOS.pdf
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