Evolution of the galaxy stellar mass function: evidence for an increasing M* from z = 2 to the present day

N J Adams,C D P Lagos,R A A Bowler,B Häußler,M J Jarvis

doi:10.1093/mnras/stab1956

Abstract

ABSTRACT Utilizing optical and near-infrared broad-band photometry covering &gt;5 deg2 in two of the most well-studied extragalactic legacy fields (COSMOS and XMM-LSS), we measure the galaxy stellar mass function (GSMF) between 0.1 &lt; z &lt; 2.0. We explore in detail the effect of two source extraction methods (SExtractor and ProFound) in addition to the inclusion/exclusion of Spitzer IRAC 3.6 and 4.5 μm photometry when measuring the GSMF. We find that including IRAC data reduces the number of massive (log10(M/M⊙) &gt; 11.25) galaxies found due to improved photometric redshift accuracy, but has little effect on the more numerous lower-mass galaxies. We fit the resultant GSMFs with double Schechter functions down to log10(M/M⊙) = 7.75 (9.75) at z = 0.1 (2.0) and find that the choice of source extraction software has no significant effect on the derived best-fitting parameters. However, the choice of methodology used to correct for the Eddington bias has a larger impact on the high-mass end of the GSMF, which can partly explain the spread in derived M* values from previous studies. Using an empirical correction to model the intrinsic GSMF, we find evidence for an evolving characteristic stellar mass with δlog10(M*/M⊙)/δz = $-0.16\pm 0.05 \, (-0.11\pm 0.05)$, when using SExtractor (ProFound). We argue that with widely quenched star formation rates in massive galaxies at low redshift (z &lt; 0.5), additional growth via mergers is required in order to sustain such an evolution to a higher characteristic mass.

Highlights

1.1 The evolution of the galaxy stellar mass functionThe galaxy stellar mass function (GSMF) is a measurement of the cumulative effects of physical processes that enhance or hinder star formation within galaxies
First we compare the results with and without the inclusion of Spitzer/IRAC [3.6] and [4.5] data, and second we compare the GSMF derived from SExtractor based photometry in comparison to that derived with Profound
The most immediately apparent feature is the offset between the GSMFs that include or exclude Spitzer/IRAC data in the redshift bins of 0.5 < z < 0.75 and 1.0 < z < 1.25

Summary

Introduction

1.1 The evolution of the galaxy stellar mass functionThe galaxy stellar mass function (GSMF) is a measurement of the cumulative effects of physical processes that enhance or hinder star formation within galaxies. Many theories have been proposed to explain why there is significant suppression in the star formation (often called quenching) of galaxies above this stellar mass, examples include but are not limited to: starvation/strangulation (Larson et al 1980; Kawata & Mulchaey 2008; McCarthy et al 2008; Feldmann et al 2011; Bahé et al 2013; Feldmann & Mayer 2015), virial shock heating (Birnboim & Dekel 2003; Dekel & Birnboim 2006; Cattaneo et al 2006) and AGN feedback (Binney & Tabor 1995; Di Matteo et al 2005; Springel et al 2005; Bower et al 2006; Croton et al 2006; Cattaneo et al 2009; Fabian 2012; Bongiorno et al 2016; Beckmann et al 2017) To adequately test these theories and increase our understanding of how these processes influence galaxy evolution, simulations are required. To increase our understanding of both quenching and merger rates, stellar mass functions have become a key benchmark for simulations in the past few years (Henriques et al 2013; Schaye et al 2015; Pillepich et al 2018; Lagos et al 2018) and require observations to be reliable in order to tune and test these simulations

Results

Discussion

Conclusion