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Published September 2017 | Published + Submitted
Journal Article Open

The COSMOS2015 galaxy stellar mass function: Thirteen billion years of stellar mass assembly in ten snapshots


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 10^(10)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.

Additional Information

© 2017 ESO. Article published by EDP Sciences. Received 10 January 2017; Accepted 17 May 2017; Published online 12 September 2017. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under ESO programme ID 179.A-2005 and on data products produced by TERAPIX and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium (http://ultravista.org/). Based on data produced by the SPLASH team from observations made with the Spitzer Space Telescope (http://splash.caltech.edu). The authors warmly thank the anonymous referee for her/his constructive comments. The authors thank Shoubaneh Hemmati and Hooshang Nayyeri for providing us with the CANDELS Multiwavelength Catalog in the COSMOS field, and Andrea Grazian and Thibault Garel for sending their results in a convenient digitalised format. I.D. thanks Marta Volonteri, Jeremy Blaizot, Yohan Dubois, Andrea Grazian, Roberto Maiolino for very useful discussions. I.D. and O.I. acknowledge funding of the French Agence Nationale de la Recherche for the SAGACE project. C.L. acknowledges support from a Beecroft fellowship. I.D. acknowledges the European Union's Seventh Framework programme under grant agreement 337595 (ERC Starting Grant, "CoSMass"). A.F. acknowledges support from the Swiss National Science Foundation. The COSMOS team in France acknowledges support from the Centre National d'Études Spatiales.

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Published - aa30419-17.pdf

Submitted - 1701.02734.pdf


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August 19, 2023
October 26, 2023