Andromeda XXV – a dwarf galaxy with a low central dark matter density. Issue 3 (14th March 2023)

• Record Type: Journal Article
• Authors: 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; Weisz, Daniel R
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 521:Issue 3(2023)
• Page Start: 3527
• Page End: 3539
• Publication Date: 2023-03-14
• Subjects: galaxies: dwarf -- galaxies: kinematics and dynamics -- galaxies: haloes -- dark matter; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stad752
• Languages: English
• ISSNs: 0035-8711

Abstract

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.