Andromeda XXV — a dwarf galaxy with a low central dark matter density [GA]

http://arxiv.org/abs/2209.15022


Andromeda (And) XXV has previously been reported as a dwarf spheroidal galaxy (dSph) with little-to-no dark matter. However, the uncertainties on this result were significant. In this study, we double the number of member stars and re-derive the kinematics and mass of And XXV. We find that And XXV has a systemic velocity of $\nu_\mathrm{r}=-107.7\pm1.0 \mathrm{~km s}^{-1}$ and a velocity dispersion of $\sigma_\nu=4.5\pm1.0\mathrm{~km s}^{-1}$. With this better constrained velocity dispersion, we derive a mass contained within the half-light radius of $M(r< r_\mathrm{h})=6.9^{+3.2}{-2.8}\times10^6\mathrm{~M}\odot$. This mass corresponds to a mass-to-light ratio of $\mathrm{[M/L]}\mathrm{r\mathrm{h}}=37^{+17}{-15}\mathrm{~M}\odot/\mathrm{L}\odot$, demonstrating, for the first time, that And XXV has an unambiguous dark matter component. We also measure the metallicity of And XXV to be $\mathrm{[Fe/H]}=-1.9\pm0.1$$\mathrm{~}$dex, which is in agreement with previous results. Finally, we extend the analysis of And XXV to include mass modelling using GravSphere. We find that And XXV has a low central dark matter density, $\rho\mathrm{DM}(150\mathrm{pc})= 2.7^{+1.8}{-1.6}\times10^7\mathrm{~M}\odot\mathrm{kpc}^{-3}$, making And XXV a clear outlier when compared to other Local Group (LG) dSphs of the similar stellar mass. In a companion paper, we will explore whether some combination of dark matter cusp-core transformations and/or tides can explain And XXV’s low density.

Read this paper on arXiv…

E. Charles, M. Collins, R. Rich, et. al.
Mon, 3 Oct 22
39/55

Comments: 13 pages, 8 figures (7 main, 1 appendix). Submitted to MNRAS