The Role of Quenching Time in the Evolution of the Mass-size Relation of Passive Galaxies from the Wisp Survey

June 2016 • 2016ApJ...824...68Z

Authors • Zanella, A. • Scarlata, C. • Corsini, E. M. • Bedregal, A. G. • Dalla Bontà, E. • Atek, H. • Bunker, A. J. • . Colbert, J. • Dai, Y. S. • Henry, A. • Malkan, M. • Martin, C. • Rafelski, M. • Rutkowski, M. J. • Siana, B. • Teplitz, H.

Abstract • We analyze how passive galaxies at z ∼ 1.5 populate the mass-size plane as a function of their stellar age, to understand if the observed size growth with time can be explained with the appearance of larger quenched galaxies at lower redshift. We use a sample of 32 passive galaxies extracted from the Wide Field Camera 3 Infrared Spectroscopic Parallel (WISP) survey with spectroscopic redshift 1.3 ≲ z ≲ 2.05, specific star formation rates lower than 0.01 Gyr^-1, and stellar masses above 4.5 × 10¹⁰ M _⊙. All galaxies have spectrally determined stellar ages from fitting of their rest-frame optical spectra and photometry with stellar population models. When dividing our sample into young (age ≤2.1 Gyr) and old (age >2.1 Gyr) galaxies we do not find a significant trend in the distributions of the difference between the observed radius and that predicted by the mass-size relation. This result indicates that the relation between the galaxy age and its distance from the mass-size relation, if it exists, is rather shallow, with a slope α ≳ -0.6. At face value, this finding suggests that multiple dry and/or wet minor mergers, rather than the appearance of newly quenched galaxies, are mainly responsible for the observed time evolution of the mass-size relation in passive galaxies.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

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James Colbert

Associate Scientist

Harry Teplitz

Senior Scientist