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

¹ INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio, Italy
e-mail: andrea.grazian@oa-roma.inaf.it
² SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ Harvard-Smithsonian Center for Astrophysics 60 Garden Street, Cambridge, MA 02138, USA
⁵ UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064, USA
⁶ Kapteyn Astronomical Institute, University of Groningen, 9700 AV Groningen, The Netherlands
⁷ California Institute of Technology, Pasadena, CA 91125, USA
⁸ Center for Astrophysics and Planetary Science, Racah Institute of Physics, The Hebrew University, 91904 Jerusalem, Israel
⁹ NOAO, 950 N. Cherry Avenue, Tucson, AZ 85719, USA
¹⁰ Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, USA
¹¹ Max Planck Institute for extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching bei Munchen, Germany
¹² Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003, USA
¹³ Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, USA
¹⁴ Physics Department Purdue University, 525 Northwestern Avenue West Lafayette, IN 47907, USA
¹⁵ Kavli Institute for Particle Astrophysics & Cosmology, Physics Department, and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
¹⁶ Department of Physics and Astronomy, UC Riverside, 900 University Ave, Riverside, CA 92521, USA
¹⁷ INAF–Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
¹⁸ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
¹⁹ INAF–Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, 35122 Padova, Italy
²⁰ University of Bologna, Department of Physics and Astronomy (DIFA), V.le Berti Pichat 6/2, 40127 Bologna, Italy
²¹ INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy

Received: 4 August 2014
Accepted: 25 November 2014

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 arcmin², 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^∗ ~ 10⁹ M_⊙ at z = 4 and ~6 × 10⁹ 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.