Stellar Mass and Velocity Functions of Galaxies: Backward evolution and the fate of Milky Way siblings

TL;DR

This study uses backward evolutionary models to analyze galaxy stellar mass and velocity functions, revealing that many Milky Way-like galaxies have quenched star formation since redshift 1, and providing a consistent picture of galaxy evolution at intermediate redshifts.

Contribution

It introduces a simple backward evolution approach linking stellar mass, SFR, and velocity functions to galaxy quenching and evolution, especially for Milky Way siblings.

Findings

50% of Milky Way-like galaxies quenched star formation since redshift 1

SMF of star-forming galaxies remains constant between redshift 0 and 1

Models successfully reproduce cosmic SFR density evolution

Abstract

We attempt in this paper to check the consistency of the observed Stellar Mass Function (SMF), SFR functions and the cosmic star formation rate density with simple backward evolutionary models. Starting from observed SMF for star-forming galaxies, we use backwards models to predict the evolution of a number of quantities, such as the SFR function, the cosmic SFR density and the Velocity Function. The velocity being a parameter attached to a galaxy during its history (contrary to the stellar mass), this approach allows us to quantify the number density evolution of galaxies of a given velocity, e.g. of the Milky Way siblings. Observations suggest that the SMF of star forming galaxies is constant between redshift 0 and 1. In order to reproduce this result, we must quench star formation in a number of star forming galaxies. The SMF of these quenched galaxies is consistent with available data concerning the increase in the population of quiescent galaxies in the same redshift interval. The SMF of quiescent galaxies is then mainly determined by the distribution of active galaxies that must stop star formation, with a modest mass redistribution during mergers. The cosmic SFR density, and the evolution of the SFR functions are relatively well recovered, although they provide some clue for a small evolution of the SMF of star forming galaxies at the lowest redshifts. We thus consider that we have obtained in a simple way a relatively consistent picture of the evolution of galaxies at intermediate redshifts. We note that if this picture is correct, 50 percent of the Milky-Way sisters (galaxies with the same velocity as our Galaxy, i.e. 220 km/s) have quenched their star formation since redshift 1 (and an even larger fraction for larger velocities). We discuss the processes that might be responsible for this transformation.