Publication: Optically faint massive Balmer break galaxies at z > 3 in the CANDELS/GOODS fields
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2019-05-10
Authors
Barro, Guillermo
Domínguez Sánchez, Helena
Eliche Moral, M. Carmen
Hernán Caballero, Antonio
Rodríguez Muñoz, Lucía
Esquej, Pilar
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IOP Publishing LTD
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Abstract
We present a sample of 33 Balmer break galaxies (BBGs) selected as Hubble Space Telescope/F160W dropouts in the deepest CANDELS/GOODS fields (H >/~ 27.3 mag) but relatively bright in Spitzer/IRAC ([3.6], [4.5] < 24.5 mag), implying red colors (median and quartiles: {H - [3.6]} = 3.1^(3.4)_(2.8) mag ). Half of these BBGs are newly identified sources. Our BBGs are massive ({ log (M/ M_(☉))} = 10.8_(10.4)^( 11.0)), high-redshift ({z} = 4.8_(4.4)^(5.1)), dusty ({A(V)} = 2.0_(1.5)^(2.0) mag) galaxies. The spectral energy distributions (SEDs) of half of our sample indicate that they are star-forming galaxies with typical specific star formation rates (SFRs) of 0.5–1.0 Gyr^(−1), qualifying them as main-sequence (MS) galaxies at 3 < z < 6. One-third of these SEDs indicate the presence of prominent emission lines (Hβ + [O III], Hα + [N II]) boosting the IRAC fluxes and red colors. Approximately 20% of the BBGs are very dusty (A (V) ∼ 2.5 mag) starbursts with strong mid-to-far-infrared detections and extreme SFRs (SFR > 10^(3) M_(☉) yr^(−1)) that place them above the MS. The rest, 30%, are post-starbursts or quiescent galaxies located >2σ below the MS with mass-weighted ages older than 700 Myr. Only two of the 33 galaxies are X-ray-detected active galactic nuclei (AGNs) with optical/near-infrared SEDs dominated by stellar emission, but the presence of obscured AGNs in the rest of the sources cannot be discarded. Our sample accounts for 8% of the total number density of log(M / M_(☉)) > 10 galaxies at z > 3, but it is a significant contributor (30%) to the general population of red log(M / M_(☉) > 11 galaxies at 4 < z < 6. Finally, our results point out that one of every 30 massive log (M / M_(☉) > 11 galaxies in the local universe was assembled in the first 1.5 Gyr after the big bang, a fraction that is not reproduced by state-of-the-art galaxy formation simulations.
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© 2019. The American Astronomical Society. We acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grants AYA2015-63650-P and BES-2013-065772. N.C. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant No. AYA2016- 75808-R, which is partly funded by the European Regional Development Fund (ERDF). 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). This research has made use of the software packages SExtractor, IRAF (Tody 1993), DAOPHOT routine, and STILTS (http://www.starlink.ac.uk/stilts/) software, provided by Mark Taylor of Bristol University, England. This work also employed Astropy, a community-developed core Python package for astronomy (Astropy Collaboration et al. 2013); APLpy, an open-source plotting package for Python (Robitaille & Bressert 2012); Matplotlib (Hunter 2007) and Numpy; and Photutils (Bradley et al. 2016).