The galaxy stellar mass function at 3.5 ≤z≤ 7.5 in the CANDELS/UDS, GOODS-South, and HUDF fields

Abstract

Context. The form and evolution of the galaxy stellar mass function (GSMF) at high redshifts provide crucial information on star formation history and mass assembly in the young Universe, close or even prior to the epoch of reionization. Aims. We used the unique combination of deep optical/near-infrared/mid-infrared imaging provided by HST, Spitzer, and the VLT in the CANDELS-UDS, GOODS-South, and HUDF fields to determine the GSMF over the redshift range 3.5 ≤ z ≤ 7.5. Methods. We used the HST WFC3/IR near-infrared imaging from CANDELS and HUDF09, reaching H 27−28.5 over a total area of 369 arcmin 2 , in combination with associated deep HST ACS optical data, deep Spitzer IRAC imaging from the SEDS programme, and deep Y and K-band VLT Hawk-I images from the HUGS programme, to select a galaxy sample with high-quality photometric redshifts. These have been calibrated with more than 150 spectroscopic redshifts in the range 3.5 ≤ z ≤ 7.5, resulting in an overall precision of σ z /(1 + z) ∼ 0.037. With this database we have determined the low-mass end of the high-redshift GSMF with unprecedented precision, reaching down to masses as low as M * ∼ 10 9 M at z = 4 and ∼6 × 10 9 M at z = 7. Results. We find that the GSMF at 3.5 ≤ z ≤ 7.5 depends only slightly on the recipes adopted to measure the stellar masses, namely the photometric redshifts, the star formation histories, the nebular contribution, or the presence of AGN in the parent sample. The low-mass end of the GSMF is steeper than has been found at lower redshifts, but appears to be unchanged over the redshift range probed here. Meanwhile the high-mass end of the GSMF appears to evolve primarily in density, although there is also some evidence of evolution in characteristic mass. Our results are very different from previous mass function estimates based on converting UV galaxy luminosity functions into mass functions via tight mass-to-light relations. Integrating our evolving GSMF over mass, we find that the growth of stellar mass density is barely consistent with the time-integral of the star formation rate density over cosmic time at z > 4. Conclusions. These results confirm the unique synergy of the CANDELS+HUDF, HUGS, and SEDS surveys for the discovery and study of moderate/low-mass galaxies at high redshifts, and reaffirm the importance of space-based infrared selection for the unbiased measurement of the evolving GSMF in the young Universe.

The Impossibly Early Galaxy Problem

“…However, recent infrared observations by the CANDELS collaboration (Duncan et al 2014;Grazian et al 2015) and SPLASH ) provide a much larger sample of high redshift galaxies with stellar mass estimates, and can now be used to estimate the halo-mass function at~-z 6 8.…”

Star Formation in Galaxies at z ∼ 4–5 from the SMUVS Survey: A Clear Starburst/Main-sequence Bimodality for Hα Emitters on the SFR–M* Plane

“…For the M 9.2 log 10.8 10 *   objects we directly adopted our derived SFR ("Hα excess" galaxies) or SFR upper limits (for the other galaxies). To account for the contribution of lower-mass galaxies, we considered that the extrapolation of the GSMF at z=4-5 Grazian et al 2015) indicates that we should expect ∼5 times more galaxies with M 8 log 9.2 10 *  < than with M log 9.2 10 *  . And according to Figure 2, the 8 log M 9.2 10 *  < objects should have on average SFR that are about 1 dex lower than the more massive galaxies.…”

GALAXY CANDIDATES AT z ∼ 10 IN ARCHIVAL DATA FROM THE BRIGHTEST OF REIONIZING GALAXIES (BORG[z8]) SURVEY

“…In addition to constraining the shape of the LF, the brightest high-z candidates identified by HST observations are also ideal targets for follow-up observations to infer stellar population properties such as ages and stellar masses (Stark et al 2009;Labbé et al 2010Labbé et al , 2015Grazian et al 2015), ionization state of the IGM (Muñoz & Loeb 2011), and spectroscopic redshift. For the latter, confirmation of photometric candidates relies typically on detection of a Lyman break in the galaxy continuum, (e.g., Malhotra et al 2005) and/or of emission lines, primarily Lyα (e.g., Stark et al 2010;Pentericci et al 2011Pentericci et al , 2014Caruana et al 2012;Schenker et al 2012;Treu et al 2012Treu et al , 2013Finkelstein et al 2013;Tilvi et al 2014;Vanzella et al 2014) or other UV lines such as C III] or C IV (Stark et al 2015a(Stark et al , 2015b.…”