On the gas content, star formation efficiency, and environmental quenching of massive galaxies in protoclusters at z ≈ 2.0-2.5

J. A. Zavala, C. M. Casey, N. Scoville, J. B. Champagne, Y. Chiang, H. Dannerbauer, P. Drew, H. Fu, J. Spilker, L. Spitler, K. V. Tran, E. Treister, S. Toft

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    We present ALMA Band 6 (ν = 233 GHz, λ = 1.3 mm) continuum observations toward 68 "normal" star-forming galaxies within two Coma-like progenitor structures at z = 2.10 and 2.47, from which ISM masses are derived, providing the largest census of molecular gas mass in overdense environments at these redshifts. Our sample comprises galaxies with a stellar mass range of 1 × 109 M-4 × 1011 M⊙; with a mean M ≈ 6 × 1010 M. Combining these measurements with multiwavelength observations and spectral energy distribution modeling, we characterize the gas mass fraction and the star formation efficiency, and infer the impact of the environment on galaxies' evolution. Most of our detected galaxies (≳70%) have star formation efficiencies and gas fractions similar to those found for coeval field galaxies and in agreement with the field scaling relations. However, we do find that the protoclusters contain an increased fraction of massive, gas-poor galaxies, with low gas fractions (f gas ≲ 6%-10%) and red rest-frame ultraviolet/optical colors typical of post-starburst and passive galaxies. The relatively high abundance of passive galaxies suggests an accelerated evolution of massive galaxies in protocluster environments. The large fraction of quenched galaxies in these overdense structures also implies that environmental quenching takes place during the early phases of cluster assembly, even before virialization. From our data, we derive a quenching efficiency of q ≈ 0.45 and an upper limit on the quenching timescale of τ q < 1 Gyr.

    Original languageEnglish
    Article number183
    Number of pages15
    JournalAstrophysical Journal
    Issue number2
    Publication statusPublished - 18 Dec 2019

    Bibliographical note

    Copyright 2019 The American Astronomical Society. First published in the Astrophysical journal, 887(2), 183, 2019, published by IOP Publishing. The original publication is available at http://www.doi.org/10.3847/1538-4357/ab5302. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


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