ZFOURGE: using composite spectral energy distributions to characterize galaxy populations at 1 < z < 4

Ben Forrest, Kim Vy H. Tran, Adam Broussard, Jonathan H. Cohn, Robert C. Kennicutt, Casey Papovich, Rebecca Allen, Michael Cowley, Karl Glazebrook, Glenn G. Kacprzak, Lalitwadee Kawinwanichakij, Themiya Nanayakkara, Brett Salmon, Lee R. Spitler, Caroline M. S. Straatman

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    21 Citations (Scopus)
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    We investigate the properties of galaxies as they shut off star formation over the 4 billion years surrounding peak cosmic star formation. To do this, we categorize ∼7000 galaxies from 1 < z < 4 into 90 groups based on the shape of their spectral energy distributions (SEDs) and build composite SEDs with R ∼ 50 resolution. These composite SEDs show a variety of spectral shapes and also show trends in parameters such as color, mass, star formation rate, and emission-line equivalent width. Using emission-line equivalent widths and strength of the 4000 Å break, D(4000), we categorize the composite SEDs into five classes: extreme emission line, star-forming, transitioning, post-starburst, and quiescent galaxies. The transitioning population of galaxies shows modest Hα emission (EWREST ∼ 40 Å) compared to more typical star-forming composite SEDs at log10(M/M⊙) ∼ 10.5 (EWREST ∼ 80 Å). Together with their smaller sizes (3 kpc vs. 4 kpc) and higher Sérsic indices (2.7 vs. 1.5), this indicates that morphological changes initiate before the cessation of star formation. The transitional group shows a strong increase of over 1 dex in number density from z ∼ 3 to z ∼ 1, similar to the growth in the quiescent population, while post-starburst galaxies become rarer at z ≲ 1.5. We calculate average quenching timescales of 1.6 Gyr at z ∼ 1.5 and 0.9 Gyr at z ∼ 2.5 and conclude that a fast-quenching mechanism producing post-starbursts dominated the quenching of galaxies at early times, while a slower process has become more common since z ∼ 2.

    Original languageEnglish
    Article number131
    Pages (from-to)1-25
    Number of pages25
    JournalAstrophysical Journal
    Issue number2
    Publication statusPublished - 20 Aug 2018

    Bibliographical note

    Copyright 2018 The American Astronomical Society. First published in the Astrophysical journal, 863(2), 131, 2018, published by IOP Publishing. The original publication is available at http://www.doi.org/10.3847/1538-4357/aad232. 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.


    • galaxies: evolution
    • galaxies: high-redshift


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