Warm dark matter constraints using Milky Way satellite observations and subhalo evolution modeling

Warm dark matter (WDM) can potentially explain small-scale observations that currently challenge the cold dark matter (CDM) model, as warm particles suppress structure formation due to free-streaming effects. Observing small-scale matter distribution provides a valuable way to distinguish between CDM and WDM. In this work, we use observations from the Dark Energy Survey and PanSTARRS1, which observe 270 Milky-Way satellites after completeness corrections. We test WDM models by comparing the number of satellites in the Milky Way with predictions derived from the Semi-Analytical SubHalo Inference Modeling (sashimi) code, which we develop based on the extended Press-Schechter formalism and subhalos' tidal evolution prescription. We robustly rule out WDM with masses lighter than 4.4 keV at 95% confidence level for the Milky-Way halo mass of 10¹² M⊙. The limits are a weak function of the (yet uncertain) Milky-Way halo mass, and vary as m_WDM ≳3.6-5.1 keV for (0.6-2.0)×10¹² M_⊙ .For the sterile neutrinos that form a subclass of WDM, we obtain the constraints of m_νs>12 keV for the Milky-Way halo mass of 10¹² M_⊙, independent of the mixing angle. These results based on sashimi do not rely on any assumptions of galaxy formation physics or are not limited by numerical resolution. The models, therefore, offer a robust and fast way to constrain the WDM models. By applying a satellite forming condition, however, we can rule out the WDM mass lighter than 9.0 keV for the Milky-Way halo mass of 10¹² M_⊙.