A New Census of the 0.2 < z < 3.0 Universe, Part I: The Stellar Mass Function

TL;DR

This paper presents a new, self-consistent measurement of the galaxy stellar mass function over redshifts 0.2 to 3, using advanced SED models that infer higher stellar masses and lower star formation rates, resolving previous tensions.

Contribution

It introduces a novel continuity modeling approach for the galaxy stellar mass function evolution, utilizing full uncertainty contours and resulting in higher mass densities than prior studies.

Findings

Higher galaxy number densities at fixed mass compared to previous measurements.

Stellar mass density approximately 50% higher, peaking at z~1.

Older stellar ages inferred by the new SED models.

Abstract

There has been a long-standing factor-of-two tension between the observed star formation rate density and the observed stellar mass buildup after $z\sim2$. Recently we have proposed that sophisticated panchromatic SED models can resolve this tension, as these methods infer systematically higher masses and lower star formation rates than standard approaches. In a series of papers we now extend this analysis and present a complete, self-consistent census of galaxy formation over $0.2 < z < 3$ inferred with the \texttt{Prospector} galaxy SED-fitting code. In this work, Paper I, we present the evolution of the galaxy stellar mass function using new mass measurements of $\sim$10$^5$ galaxies in the 3D-HST and COSMOS-2015 surveys. We employ a new methodology to infer the mass function from the observed stellar masses: instead of fitting independent mass functions in a series of fixed redshift intervals, we construct a continuity model that directly fits for the redshift evolution of the mass function. This approach ensures a smooth picture of galaxy assembly and makes use of the full, non-Gaussian uncertainty contours in our stellar mass inferences. The resulting mass function has higher number densities at a fixed stellar mass than almost any other measurement in the literature, largely owing to the older stellar ages inferred by \texttt{Prospector}. The stellar mass density is $\sim$50% higher than previous measurements, with the offset peaking at $z\sim1$. The next two papers in this series will present the new measurements of star-forming main sequence and the cosmic star formation rate density, respectively.