The COSMOS2015 galaxy stellar mass function

Thirteen billion years of stellar mass assembly in ten snapshots^⋆

¹ Aix-Marseille Univ., CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France
e-mail: iary.davidzon@lam.fr
² INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
³ Sub-department of Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁴ Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
⁵ Sorbonne Universités, UPMC University Paris 6 and CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis bd Arago, 75014 Paris, France
⁶ Department of Physics, University of Zagreb, Bijenička cesta 32, 10002 Zagreb, Croatia
⁷ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
⁸ Academia Sinica Institute of Astronomy and Astrophysics, PO Box 23-141, 10617 Taipei, Taiwan, PR China
⁹ Centre de Recherche Astrophysique de Lyon, Université de Lyon, Université Lyon 1, CNRS, Observatoire de Lyon, 9 avenue Charles André, 69561 Saint-Genis Laval Cedex, France
¹⁰ Laboratoire AIM Paris-Saclay, UMR 7158, CEA, CNRS, Université Paris VII, CE-SACLAY, Bât. 709, 91191 Gif-sur-Yvette, France
¹¹ Dark Cosmology Centre, Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen O, Denmark
¹² Institute for Astronomy, 2680 Woodlawn Drive Honolulu, HI 96822-1839, USA
¹³ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
¹⁴ Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
¹⁵ Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, The University of Tokyo, Kashiwa, 277-8583 Chiba, Japan

Received: 10 January 2017
Accepted: 17 May 2017

Abstract

We measure the stellar mass function (SMF) and stellar mass density of galaxies in the COSMOS field up to z ~ 6. We select them in the near-IR bands of the COSMOS2015 catalogue, which includes ultra-deep photometry from UltraVISTA-DR2, SPLASH, and Subaru/Hyper Suprime-Cam. At z> 2.5 we use new precise photometric redshifts with error σ_z = 0.03(1 + z) and an outlier fraction of 12%, estimated by means of the unique spectroscopic sample of COSMOS (~100 000 spectroscopic measurements in total, more than one thousand having robust z_spec> 2.5). The increased exposure time in the DR2, along with our panchromatic detection strategy, allow us to improve the completeness at high z with respect to previous UltraVISTA catalogues (e.g. our sample is >75% complete at 10¹⁰ ℳ_⊙ and z = 5). We also identify passive galaxies through a robust colour–colour selection, extending their SMF estimate up to z = 4. Our work provides a comprehensive view of galaxy-stellar-mass assembly between z = 0.1 and 6, for the first time using consistent estimates across the entire redshift range. We fit these measurements with a Schechter function, correcting for Eddington bias. We compare the SMF fit with the halo mass function predicted from ΛCDM simulations, finding that at z> 3 both functions decline with a similar slope in thehigh-mass end. This feature could be explained assuming that mechanisms quenching star formation in massive haloes become less effective at high redshifts; however further work needs to be done to confirm this scenario. Concerning the SMF low-mass end, it shows a progressive steepening as it moves towards higher redshifts, with α decreasing from -1.47^+0.02_-0.02 at z ≃ 0.1 to -2.11^+0.30_-0.13 at z ≃ 5. This slope depends on the characterisation of the observational uncertainties, which is crucial to properly remove the Eddington bias. We show that there is currently no consensus on the method to quantify such errors: different error models result in different best-fit Schechter parameters.