Andromeda XXV – a dwarf galaxy with a low central dark matter density

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 fin...

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Veröffentlicht in:Mon.Not.Roy.Astron.Soc 2023-03, Vol.521 (3), p.3527-3539
Hauptverfasser: 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
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Sprache:eng
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Zusammenfassung: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.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stad752