Faint dwarfs as a test of DM models: WDM vs. CDM

TL;DR

This study uses high-resolution simulations to compare dwarf galaxy formation in WDM and CDM cosmologies, revealing differences in star formation timing, gas outflows, and stellar distribution that align with observations and help distinguish dark matter models.

Contribution

It demonstrates the impact of dark matter type on dwarf galaxy evolution, emphasizing the importance of baryon physics in simulations for model differentiation.

Findings

WDM delays star formation by 1-2 Gyr compared to CDM.

Gas outflows lower central mass density regardless of DM model.

Simulated star formation bursts match observed dwarf galaxy properties.

Abstract

We use high resolution Hydro$+$N-Body cosmological simulations to compare the assembly and evolution of a small field dwarf (stellar mass ~ 10$^{6-7}$ M$\odot$, total mass 10$^{10}$ M$\odot$ in $\Lambda$ dominated CDM and 2keV WDM cosmologies. We find that star formation (SF) in the WDM model is reduced and delayed by 1-2 Gyr relative to the CDM model, independently of the details of SF and feedback. Independent of the DM model, but proportionally to the SF efficiency, gas outflows lower the central mass density through `dynamical heating', such that all realizations have circular velocities $<$ 20kms at 500$~$pc, in agreement with local kinematic constraints. As a result of dynamical heating, older stars are less centrally concentrated than younger stars, similar to stellar population gradients observed in nearby dwarf galaxies. Introducing an important diagnostic of SF and feedback models, we translate our simulations into artificial color-magnitude diagrams and star formation histories in order to directly compare to available observations. The simulated galaxies formed most of their stars in many $\sim$10 Myr long bursts. The CDM galaxy has a global SFH, HI abundance and Fe/H and alpha-elements distribution well matched to current observations of dwarf galaxies. These results highlight the importance of directly including `baryon physics' in simulations when 1) comparing predictions of galaxy formation models with the kinematics and number density of local dwarf galaxies and 2) differentiating between CDM and non-standard models with different DM or power spectra.