Dwarf Galaxies as Cosmological Probes

TL;DR

This paper reviews how dwarf galaxies serve as tests for the LCDM model, discussing challenges and predictions, and emphasizing the importance of detecting dark, low-mass halos to validate the theory.

Contribution

It clarifies that challenges like the missing satellites problem are not insurmountable and highlights the testable prediction of dark mini-halos in LCDM.

Findings

Most dwarf galaxies inhabit halos of similar mass.

A minimum halo mass threshold is necessary for galaxy formation.

Detection of dark mini-halos would strongly support LCDM.

Abstract

The Lambda Cold Dark Matter (LCDM) paradigm makes specific predictions for the abundance, structure, substructure and clustering of dark matter halos, the sites of galaxy formation. These predictions can be directly tested, in the low-mass halo regime, by dark matter-dominated dwarf galaxies. A number of potential challenges to LCDM have been identified when confronting the expected properties of dwarfs with observation. I review our understanding of a few of these issues, including the `missing satellites' and the `too-big-to-fail' problems, and argue that neither poses an insurmountable challenge to LCDM. Solving these problems requires that most dwarf galaxies inhabit halos of similar mass, and that there is a relatively sharp minimum halo mass threshold to form luminous galaxies. These predictions are eminently falsifiable. In particular, LCDM predicts a large number of `dark' low-mass halos, some of which should have retained enough primordial gas to be detectable in deep 21 cm or H$_\alpha$ surveys. Detecting this predicted population of `mini-halos' would be a major discovery and a resounding success for LCDM on small scales.