Constraining the Milky Way Mass with Its Hot Gaseous Halo

TL;DR

This paper introduces a new method to estimate the Milky Way's total mass using observations of its hot gaseous halo's temperature distribution, accounting for non-thermal pressure support and different density profiles.

Contribution

The authors develop a novel approach linking corona temperature observations to the Milky Way's mass, considering various density profiles and non-thermal pressures, independent of total corona mass or metallicity.

Findings

Estimated Milky Way virial mass ranges from 1.19 to 2.95 trillion solar masses for cored profiles.

For cuspy profiles with baryons, the mass range is 1.34 to 5.44 trillion solar masses.

Non-thermal pressure support increases the estimated mass, while outward acceleration could lower it.

Abstract

We propose a novel method to constrain the Milky Way (MW) mass $M_{\rm vir}$ with its corona temperature observations. For a given corona density profile, one can derive its temperature distribution assuming a generalized equilibrium model with non-thermal pressure support. While the derived temperature profile decreases substantially with radius, the X-ray-emission-weighted average temperature, which depends most sensitively on $M_{\rm vir}$, is quite uniform toward different sight lines, consistent with X-ray observations. For an Navarro-Frenk-White (NFW) total matter distribution, the corona density profile should be cored, and we constrain $M_{\rm vir}=(1.19$ - $2.95) \times 10^{12} M_{\rm sun}$. For a total matter distribution contributed by an NFW dark matter profile and central baryons, the corona density profile should be cuspy and $M_{\rm vir,dm}=(1.34$ - $5.44) \times 10^{12} M_{\rm sun}$. Non-thermal pressure support leads to even higher values of $M_{\rm vir}$, while a lower MW mass may be possible if the corona is accelerating outward. This method is independent of the total corona mass, its metallicity, and temperature at very large radii.