Abstract
Accurately mapping the mass profiles of low mass dwarf spheroidal (dSph)
galaxies allows us to test predictions made by dark matter (DM) models. To
date, such analyses have primarily been performed on Milky Way (MW) satellites.
Meanwhile, the Andromeda Galaxy (M31) is home to 35 known dwarf galaxies, yet
only two have been successfully mass-modeled so far. In order to better
understand the nature of dark matter, a more comprehensive study of Local Group
dwarfs is necessary. In this study, we have undertaken a dynamical study of two
higher-luminosity Andromeda dwarf galaxies: Andromeda VI (And VI) and Andromeda
XXIII (And XXIII). We infer an enclosed mass for And VI of M(r < r$_{\rm{h}}$)
= (4.9 $\pm$ 1.5) $\times$ 10$^{7}$ M$_{\odot}$, corresponding to a
mass-to-light ratio of $[M/L]_{r_{\rm{h}}}$ = (27.1 $\pm$ 8.2)
M$_{\odot}$/L$_{\odot}$. We infer an enclosed mass for And XXIII of M(r <
r$_{\rm{h}}$) = (3.1 $\pm$ 1.9) $\times$ 10$^{7}$ M$_{\odot}$, corresponding to
a mass-to-light ratio of $[M/L]_{\rm{r_{h}}}$ = (90.2 $\pm$ 53.9)
M$_{\odot}$/L$_{\odot}$. Using the dynamical Jeans modeling tool, GravSphere,
we determine And VI and And XXIII's dark matter density at 150 pc, finding
$\rho_{\rm{DM,VI}}$(150 pc) = (1.4 $\pm$ 0.5) $\times$ 10$^{8}$ M$_{\odot}$
kpc$^{-3}$ and $\rho_{\rm{DM,XXIII}}$(150 pc) = 0.5$\substack{+0.4 \\ -0.3}
\times$ 10$^{8}$ M$_{\odot}$ kpc$^{-3}$. Our results make And VI the first
mass-modeled M31 satellite to fall into the cuspy regime, while And XXIII has a
lower density, implying either a more cored central dark matter density, or a
lowering of the density through tides. This adds And XXIII to a growing list of
M31 dwarfs with a central density lower than most MW dwarfs and lower than
expected for isolated dwarfs in the Standard Cosmology. This could be explained
by the M31 dwarfs having experienced stronger tides than their Milky Way
counterparts.