The massive end of the luminosity and stellar mass functions: Dependence on the fit to the light profile

TL;DR

This study shows that the method used to fit galaxy light profiles significantly affects the estimated stellar mass function, especially at the high-mass end, impacting our understanding of galaxy growth and mass assembly.

Contribution

It provides a detailed comparison of luminosity and stellar mass functions based on different light profile fits, highlighting the impact on massive galaxy measurements.

Findings

PyMorph fits yield more light and larger stellar masses.

The stellar mass density at z~0.1 is 1.2 times larger than previous estimates.

Number density of massive galaxies is about 5 times higher at M* > 6 x 10^{11} Msun.

Abstract

In addition to the large systematic differences arising from assumptions about the stellar mass-to-light ratio, the massive end of the stellar mass function is rather sensitive to how one fits the light profiles of the most luminous galaxies. We quantify this by comparing the luminosity and stellar mass functions based on SDSS cmodel magnitudes, and PyMorph single-Sersic and Sersic-Exponential fits to the surface brightness profiles of galaxies in the SDSS. The PyMorph fits return more light, so that the predicted masses are larger than when cmodel magnitudes are used. As a result, the total stellar mass density at z~0.1 is about 1.2x larger than in our previous analysis of the SDSS. The differences are most pronounced at the massive end, where the measured number density of objects having M* > 6 x 10^{11} Msun is ~5x larger. Alternatively, at number densities of 10^{-6} Mpc^{-3}, the limiting stellar mass is 2x larger. The differences with respect to fits by other authors, typically based on Petrosian-like magnitudes, are even more dramatic, although some of these differences are due to sky-subtraction problems, and are sometimes masked by large differences in the assumed $M_*/L$ (even after scaling to the same IMF). Our results impact studies of the growth and assembly of stellar mass in galaxies, and of the relation between stellar and halo mass, so we provide simple analytic fits to these new luminosity and stellar mass functions and quantify how they depend on morphology, as well as the binned counts in electronic format.