COSMOS2020: The galaxy stellar mass function

Abstract

Context. How galaxies form, assemble, and cease their star formation is a central question within the modern landscape of galaxy evolution studies. These processes are indelibly imprinted on the galaxy stellar mass function (SMF), and its measurement and understanding is key to uncovering a unified theory of galaxy evolution. Aims. We present constraints on the shape and evolution of the galaxy SMF, the quiescent galaxy fraction, and the cosmic stellar mass density across 90% of the history of the Universe from z = 7.5 → 0.2 as a means to study the physical processes that underpin galaxy evolution. Methods. The COSMOS survey is an ideal laboratory for studying representative galaxy samples. Now equipped with deeper and more homogeneous near-infrared coverage exploited by the COSMOS2020 catalog, we leverage the large 1.27 deg2 effective area to improve sample statistics and understand spatial variations (cosmic variance) – particularly for rare, massive galaxies – and push to higher redshifts with greater confidence and mass completeness than previous studies. We divide the total stellar mass function into star-forming and quiescent subsamples through NUVrJ color-color selection. The measurements are then fit with single- and double-component Schechter functions to infer the intrinsic galaxy stellar mass function, the evolution of its key parameters, and the cosmic stellar mass density out to z = 7.5. Finally, we compare our measurements to predictions from state-of-the-art cosmological simulations and theoretical dark matter halo mass functions. Results. We find a smooth, monotonic evolution in the galaxy stellar mass function since z = 7.5, in general agreement with previous studies. The number density of star-forming systems have undergone remarkably consistent growth spanning four decades in stellar mass from z = 7.5 → 2 whereupon high-mass systems become predominantly quiescent (“downsizing”). Meanwhile, the assembly and growth of low-mass quiescent systems only occurred recently, and rapidly. An excess of massive systems at z ≈ 2.5 − 5.5 with strikingly red colors, with some being newly identified, increase the observed number densities to the point where the SMF cannot be reconciled with a Schechter function. Conclusions. Systematics including cosmic variance and/or active galactic nuclei contamination are unlikely to fully explain this excess, and so we speculate that they may be dust-obscured populations similar to those found in far infrared surveys. Furthermore, we find a sustained agreement from z ≈ 3 − 6 between the stellar and dark matter halo mass functions for the most massive systems, suggesting that star formation in massive halos may be more efficient at early times.

Constraints on the Faint End of the Galaxy Stellar Mass Function at z ≃ 4–8 from Deep JWST Data

“…We will focus our discussion on the evolution of the low stellar mass end slope and cosmic stellar mass density (CSMD), but we also test for consistency and evolution of the other parameters, M * and f * . However, we refer the reader to Davidzon et al (2017) and Weaver et al (2023) for a more comprehensive analysis of these other parameters.…”

“…In recent years, different methods to estimate mass completeness have been developed. In particular, for our analysis, we follow the method proposed by Pozzetti et al (2010), which is commonly used in the literature (e.g., Davidzon et al 2017;Weaver et al 2023).…”

“…Some of these works have also investigated the GSMF's dependence on galaxy types, such as star-forming/quiescent galaxies (e.g., Davidzon et al 2017), central/satellite galaxies (e.g., Yang et al 2009), and galaxy morphology (Ilbert et al 2010). Moreover, the evolution of the GSMF with cosmic time provides information on the different physical processes that shape galaxy assembly (e.g., supernova and supermassive black hole feedback and mergers) and clues to understand star formation and quenching mechanisms in galaxies of different stellar masses (e.g., Peng et al 2010;Weaver et al 2023).…”

JADES: Resolving the Stellar Component and Filamentary Overdense Environment of Hubble Space Telescope (HST)-dark Submillimeter Galaxy HDF850.1 at z = 5.18

“…As one of the most massive galaxies found in the z > 5 Universe, the SFR of HDF850.1 is slightly above that expected from the star-forming main sequence. We note that z > 5 galaxies with similar stellar mass are rare with regard to volume density (10 −5 cMpc −3 dex −1 ; e.g., Weaver et al 2023), and thus, such a mass and redshift parameter space can be underweighted for the determination of star-forming main sequence across cosmic time. The high dust attenuation, high obscured fraction of SFR (SFR UV /SFR total < 10 −3 for HDF850.1), and high incompleteness in spectroscopic confirmation and (sub) millimeter SED constraints make the mainsequence SFR of such galaxies even more uncertain before the era of the JWST.…”

Star Formation and AGN Activity 500 Myr after the Big Bang: Insights from JWST

“…(2016) that are computed from similar Spitzer/IRAC observations in the CANDELS and Hubble Ultra Deep fields asStefanon et al (2021). We also investigated the z ≈ 5-7 SMFs fromWeaver et al (2023) that use the COSMOS2020 catalog. We compared these two SMFs with theStefanon et al (2021) SMFs at z = 6-7, which is the redshift range where the three studies overlap.The normalization and the pivot mass of the Weaver et al(2023) SMFs, instead of the Song et al (2016) SMFs, best agree with Stefanon et al (2021), as the systematic offset of these fitted parameters between studies is lower and the parameters themselves are better constrained by Weaver et al (2023).…”