1. Andromeda XXV – a dwarf galaxy with a low central dark matter density.
- Author
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Charles, Emily J E, Collins, Michelle L M, Rich, R Michael, Read, Justin I, Kim, Stacy Y, Ibata, Rodrigo A, Martin, Nicolas F, Chapman, Scott C, Balbinot, Eduardo, and Weisz, Daniel R
- Subjects
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DARK matter , *DWARF galaxies , *ELLIPTICAL galaxies , *STELLAR mass , *DENSITY , *GALACTIC dynamics - Abstract
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 nearly 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 νr = −107.7 ± 1.0 kms−1 and a velocity dispersion of |$\sigma _{\rm \nu }=3.7^{+1.2}_{-1.1}$| kms−1. With this updated velocity dispersion and a new literature measurement of the radial surface brightness profile, we derive a mass contained within the half-light radius of |$M(r\lt r_{\rm h})=4.7^{+3.0}_{-2.9}\times 10^6$| M⊙. This mass corresponds to a mass-to-light ratio of |$\text{[M/L]}_{\rm r_{h}}=25^{+17}_{-16}$| M⊙/L⊙, demonstrating that And XXV is most-likely dark matter dominated. We also measure the metallicity of And XXV to be |$\rm [Fe/H]=-1.9\pm 0.1$| 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, ρDM(150 pc) = |$2.3^{+1.4}_{-1.1}\times 10^7$| M⊙ kpc−3, which makes And XXV a clear outlier when compared to other local group 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. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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