Milky Way mass constraints from the Galactic satellite gap

TL;DR

This study constrains the Milky Way's halo mass using satellite velocity distributions from cosmological simulations, finding it likely lies between 0.25 and 1.4 trillion solar masses, consistent with observed satellite properties.

Contribution

It introduces a method to estimate the Milky Way's halo mass by analyzing satellite velocity gaps within a ΛCDM framework using Millennium II simulation data.

Findings

Milky Way halo mass constrained between 0.25 and 1.4×10^{12} M_⊙.

The satellite velocity gap supports the galaxy being in the tail of the expected distribution.

The results address the 'too-big-to-fail' problem and satellite rarity considerations.

Abstract

We use the distribution of maximum circular velocities, $V_{max}$, of satellites in the Milky Way (MW) to constrain the virial mass, $M_{200}$, of the Galactic halo under an assumed prior of a $\Lambda$CDM universe. This is done by analysing the subhalo populations of a large sample of halos found in the Millennium II cosmological simulation. The observation that the MW has at most three subhalos with $V_{max}\ge30 km/s$ requires a halo mass $M_{200}\le1.4\times10^{12} M_\odot$, while the existence of the Magellanic Clouds (assumed to have $V_{max}\ge60 km/s$) requires $M_{200}\ge1.0\times10^{12} M_\odot$. The first of these conditions is necessary to avoid the "too-big-to-fail" problem highlighted by Boylan-Kolchin et al., while the second stems from the observation that massive satellites like the Magellanic Clouds are rare. When combining both requirements, we find that the MW halo mass must lie in the range $0.25 \le M_{200}/(10^{12} M_\odot) \le 1.4$ at $90\%$ confidence. The gap in the abundance of Galactic satellites between $30 km/s\le V_{max} \le 60 km/s$ places our galaxy in the tail of the expected satellite distribution.