Galaxy formation with cold gas accretion and evolving stellar initial mass function

TL;DR

This paper presents a semi-analytical galaxy formation model incorporating cold gas accretion, tidal stripping, and an evolving stellar initial mass function, successfully addressing discrepancies between observations and previous models.

Contribution

It introduces a combined approach with cold gas accretion, tidal stripping, and a variable IMF to better match observed galaxy properties across redshifts.

Findings

Predicts massive high-redshift galaxies with mild evolution

Reproduces the star formation rate-stellar mass relation across redshifts

Partly resolves the stellar mass density and star formation history discrepancy

Abstract

The evolution of the galaxy stellar mass function is especially useful to test the current model of galaxy formation. Observational data have revealed a few inconsistencies with predictions from the $\Lambda {\rm CDM}$ model. For example, most massive galaxies have already been observed at very high redshifts, and they have experienced only mild evolution since then. In conflict with this, semi-analytical models of galaxy formation predict an insufficient number of massive galaxies at high redshift and a rapid evolution between redshift 1 and 0 . In addition, there is a strong correlation between star formation rate and stellar mass for star-forming galaxies, which can be roughly reproduced with the model, but with a normalization that is too low at high redshift. Furthermore, the stellar mass density obtained from the integral of the cosmic star formation history is higher than the measured one by a factor of 2. In this paper, we study these issues using a semi-analytical model that includes: 1) cold gas accretion in massive halos at high redshift; 2) tidal stripping of stellar mass from satellite galaxies; and 3) an evolving stellar initial mass function (bottom-light) with a higher gas recycle fraction. Our results show that the combined effects from 1) and 2) can predict sufficiently massive galaxies at high redshifts and reproduce their mild evolution at low redshift, While the combined effects of 1) and 3) can reproduce the correlation between star formation rate and stellar mass for star-forming galaxies across wide range of redshifts. A bottom-light/top-heavy stellar IMF could partly resolve the conflict between the stellar mass density and cosmic star formation history.