Can dwarf spheroidal galaxies host a central black hole ?

TL;DR

This study constrains the possible central black hole masses in dwarf spheroidal galaxies using mass models and kinematic data, establishing an upper limit and relating it to the black hole mass-velocity dispersion relation.

Contribution

It provides the first upper limits on black hole masses in dwarf spheroidal galaxies and constructs a unified $M_{\bullet}$--$\sigma$ relation including these systems.

Findings

95% credible upper limit of $\log(M_{\bullet}/M_{\odot}) < 6$

Constructed a unified $M_{\bullet}$--$\sigma$ relation spanning $\sigma \sim 10$--$300$ km/s

Black hole growth models are consistent with the derived upper limits

Abstract

We construct mass models of Milky Way dwarf spheroidal galaxies to place constraints on the central black hole (BH) masses they can host. We model the galaxies as a three-component system consisting of the stars, dark matter halo, and a central black hole, using the Osipkov--Merritt--Cuddeford class of anisotropic distribution function. The posterior distribution of black hole mass remains flat toward the low-mass end, indicating that the kinematic data places an upper limit on the black hole mass. Our analysis yields a 95% credible upper limit of $\log(M_{\bullet}/M_{\odot}) < 6$. We combine our results with black hole mass measurements and upper limits from the literature to construct a unified $M_{\bullet}$--$\sigma_{}$ relation spanning $\sigma_{} \sim 10$--$300,\mathrm{km,s^{-1}}$, described by $\log(M_{\bullet}) = 8.32 + 4.08,\log\left(\sigma_{}/200,\mathrm{km,s^{-1}}\right)$, with an intrinsic scatter of $\sigma_{\rm int} = 0.55$. We compare the inferred limits to models of black hole growth via momentum-driven accretion and stellar capture, which predict black hole masses in the range $10^{3}$--$10^{4},M_{\odot}$ for the range $\sigma_{} \sim 6$--$12,\mathrm{km,s^{-1}}$, in close agreement with the $M_{\bullet}$--$\sigma_{*}$ relation within the 95% credible upper limits on the black hole masses derived in this work.