The COSMOS2015 galaxy stellar mass function

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 SuprimeCam. 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 the high-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.

Constraints on the Evolution of the Galaxy Stellar Mass Function. II. The Quenching Timescale of Galaxies and Its Implication for Their Star Formation Rates

“…A similar picture can be drawn from Figure 5, which shows the predictions of our model calibrated with COS-MOS (symbols and lines have the same meaning as in Figure 4) and a comparison with the Davidzon et al (2017) data. Although the scatter in this case is distributed differently, the main features seen before still hold.…”

“…We set the model in order to perfectly match the observed SMF at z match , assign an SFR to galaxies by means of the SFR-M * relation at z match or z f orm , and let the SFRs evolve according to functional forms that mainly depend on two characteristic quenching timescales. We took advantage of observed SMFs from four surveys: ZFOURGE (Tomczak et al 2014), UltraVISTA (Ilbert et al 2013), COSMOS (Davidzon et al 2017), and a mock combination of ZFOURGE and UltraVISTA that we have called HYBRID. From the predictions of our model, we can conclude the following:…”

“…In this study, we take advantage of observed highredshift data from three different surveys: ZFOURGE (Tomczak et al 2014;Straatman et al 2016), UltraV-ISTA (Ilbert et al 2013) and COSMOS (Davidzon et al 2017). These surveys differs from one another in the total area covered, mass completeness limit, and number statistics.…”

“Super-deblended” Dust Emission in Galaxies. I. The GOODS-North Catalog and the Cosmic Star Formation Rate Density out to Redshift 6

“…four lowest redshift bins, where * M star for star-forming galaxies is estimated to be in the range of 10 10.3 - M 10 10.9 at < < z 0.2 2.5 according to Davidzon et al (2017), Ilbert et al (2013), and Muzzin et al (2013).…”

“…At > z 3, estimates of * M star fall in the range  -M 10 10.74 11.56 (Ilbert et al 2013;Muzzin et al 2013;Grazian et al 2015;Davidzon et al 2017). At these redshifts, the FIR+mm sample can only probe a small number of galaxies at the high-mass end of the SMF.…”