Star Formation and Stellar Mass Assembly in Dark Matter Halos: From Giants to Dwarfs

TL;DR

This study updates an empirical galaxy formation model with recent data, revealing how star formation and assembly histories vary across galaxy types and masses, from early universe to present day.

Contribution

It provides new insights into galaxy star formation histories and assembly processes across different mass scales and cosmic times, based on an updated empirical model.

Findings

Low-mass haloes host significant star formation at high redshift.

Most stars in cluster centrals formed before z≈2 but assembled later.

Milky Way mass galaxies have ongoing star formation without major mergers since z≈2.

Abstract

The empirical model of Lu et al. 2014 is updated with recent data and used to study galaxy star formation and assembly histories. At $z > 2$, the predicted galaxy stellar mass functions are steep, and a significant amount of star formation is hosted by low-mass haloes that may be missed in current observations. Most of the stars in cluster centrals formed earlier than $z\approx 2$ but have been assembled much later. Milky Way mass galaxies have had on-going star formation without significant mergers since $z\approx 2$, and are thus free of significant (classic) bulges produced by major mergers. In massive clusters, stars bound in galaxies and scattered in the halo form a homogeneous population that is old and with solar metallicity. In contrast, in Milky Way mass systems the two components form two distinct populations, with halo stars being older and poorer in metals by a factor of $\approx 3$. Dwarf galaxies in haloes with $M_{\rm h} < 10^{11}h^{-1}M_{\odot}$ have experienced a star formation burst accompanied by major mergers at $z > 2$, followed by a nearly constant star formation rate after $z = 1$. The early burst leaves a significant old stellar population that is distributed in spheroids.