What is the (Dark) Matter with Dwarf Galaxies?

TL;DR

This paper uses cosmological hydrodynamical simulations to study dwarf galaxy formation, revealing discrepancies between simulated galaxy luminosities and observed galaxy abundances in a Lambda CDM universe.

Contribution

It provides detailed simulations of dwarf galaxy formation in specific haloes, highlighting differences from observed dwarf galaxy properties and discussing implications for cosmological models.

Findings

Simulated dwarf galaxies have higher luminosities than observed for similar halo masses.

Final stellar masses range from 5 x 10^7 to 10^8 solar masses.

Simulations produce structures consistent with dwarf ellipticals and irregulars.

Abstract

We present cosmological hydrodynamical simulations of the formation of dwarf galaxies in a representative sample of haloes extracted from the Millennium-II Simulation. Our six haloes have a z = 0 mass of ~10^10 solar masses and show different mass assembly histories which are reflected in different star formation histories. We find final stellar masses in the range 5 x 10^7 - 10^8 solar masses, consistent with other published simulations of galaxy formation in similar mass haloes. Our final objects have structures and stellar populations consistent with dwarf elliptical and dwarf irregular galaxies. However, in a Lambda CDM universe, 10^10 solar mass haloes must typically contain galaxies with much lower stellar mass than our simulated objects if they are to match observed galaxy abundances. The dwarf galaxies formed in our own and all other current hydrodynamical simulations are more than an order of magnitude more luminous than expected for haloes of this mass. We discuss the significance and possible implications of this result.