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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]

Andromeda XXI (And XXI) has been proposed as a dwarf spheroidal galaxy with a central dark matter density that is lower than expected in the standard |$\Lambda$| cold dark matter (⁠|$\Lambda$| CDM) cosmology. In this work, we present dynamical observations for 77 member stars in this system, more than doubling previous studies to determine whether this galaxy is truly a low-density outlier. We measure a systemic velocity of |$v_r=-363.4\pm 1.0{\rm \, km\, s^{-1}}$| and a velocity dispersion of |$\sigma _v=6.1^{+1.0}_{-0.9}{\rm \, km\, s^{-1}}$|⁠ , consistent with previous work and within |$1\sigma$| of predictions made using the modified Newtonian dynamics framework. We also measure the metallicity of our member stars from their spectra, finding a mean value of |${\rm [Fe/H]}=-1.7\pm 0.1$|  dex. We model the dark matter density profile of And XXI using an improved version of gravsphere , finding a central density of |$\rho _{\rm DM}({\rm 150 pc})=2.6_{-1.5}^{+2.4} \times 10^7 \, {\rm M_\odot \, kpc^{-3}}$| at 68 per cent confidence, and a density at two half-light radii of |$\rho _{\rm DM}({\rm 1.75 kpc})=0.9_{-0.2}^{+0.3} \times 10^6 \, {\rm M_\odot \, kpc^{-3}}$| at 68 per cent confidence. These are both a factor of |${\sim }3\!-\!5$| lower than the densities expected from abundance matching in |$\Lambda$| CDM. We show that this cannot be explained by 'dark matter heating' since And XXI had too little star formation to significantly lower its inner dark matter density, while dark matter heating only acts on the profile inside the half-light radius. However, And XXI's low density can be accommodated within |$\Lambda$| CDM if it experienced extreme tidal stripping (losing |${\gt}95{{\ \rm per\ cent}}$| of its mass), or if it inhabits a low-concentration halo on a plunging orbit that experienced repeated tidal shocks. [ABSTRACT FROM AUTHOR]

We present new FLAMES+GIRAFFE spectroscopy of 36 member stars in the isolated Local Group dwarf spheroidal galaxy Tucana. We measure a systemic velocity for the system of |$v_{\mathrm{Tuc}} = 216.7_{-2.8}^{+2.9}$|  km s−1, and a velocity dispersion of |$\sigma _{\mathrm{v,Tuc}} = 14.4_{-2.3}^{+2.8}$|  km s−1. We also detect a rotation gradient of |$\frac{{\rm d}v_{r}}{{\rm d}\chi } = 7.6^{+4.2}_{-4.3}$| km s−1 kpc−1, which reduces the systemic velocity to |$v_{\mathrm{Tuc}} = 215.2_{-2.7}^{+2.8}$| km s−1 and the velocity dispersion to |$\sigma _{v,\mathrm{Tuc}} = 13.3_{-2.3}^{+2.7}$| km s−1. We perform Jeans modelling of the density profile of Tucana, using the line-of-sight velocities of the member stars. We find that it favours a high central density consistent with 'pristine' subhaloes in Λ cold dark matter, and a massive dark matter halo (∼1010 M⊙) consistent with expectations from abundance matching. Tucana appears to be significantly more centrally dense than other isolated Local Group dwarfs, making it an ideal laboratory for testing dark matter models. [ABSTRACT FROM AUTHOR]

We present a new technique to probe the central dark matter (DM) density profile of galaxies that harnesses both the survival and observed properties of star clusters. As a first application, we apply our method to the 'ultra-faint' dwarf Eridanus II (Eri II) that has a lone star cluster ∼45 pc from its centre. Using a grid of collisional N -body simulations, incorporating the effects of stellar evolution, external tides and dynamical friction, we show that a DM core for Eri II naturally reproduces the size and the projected position of its star cluster. By contrast, a dense cusped galaxy requires the cluster to lie implausibly far from the centre of Eri II (>1 kpc), with a high inclination orbit that must be observed at a particular orbital phase. Our results, therefore, favour a DM core. This implies that either a cold DM cusp was 'heated up' at the centre of Eri II by bursty star formation or we are seeing an evidence for physics beyond cold DM. [ABSTRACT FROM AUTHOR]

We present a chemodynamical analysis of the Leo V dwarf galaxy, based on the Keck II DEIMOS spectra of eight member stars. We find a systemic velocity for the system of (vr) = 170.9-1.9+2.1 kms-1 and barely resolve a velocity dispersion for the system, with σvr = 2.3-1.6+3.2 kms-1, consistent with previous studies of Leo V. The poorly resolved dispersion means we are unable to adequately constrain the dark-matter content of Leo V. We find an average metallicity for the dwarf of [Fe/H] =-2.48 ± 0.21 and measure a significant spread in the iron abundance of its member stars, with -3.1 ≤ [Fe/H] ≤ -1.9 dex, which clearly identifies Leo V as a dwarf galaxy that has been able to self-enrich its stellar population through extended star formation. Owing to the tentative photometric evidence for the tidal substructure around Leo V, we also investigate whether there is any evidence for tidal stripping or shocking of the system within its dynamics. We measure a significant velocity gradient across the system, of dv/dx = -4.1-2.6+2.8 kms-1 arcmin-1 (or dv/dx = -71.9-45.6+50.8 kms-1 kpc-1), which points almost directly towards the Galactic Centre. We argue that Leo V is likely a dwarf on the brink of dissolution, having just barely survived a past encounter with the centre of the Milky Way. [ABSTRACT FROM AUTHOR]

We investigate the claim that all dwarf spheroidal galaxies (dSphs) reside within halos that share a common, universal mass profile as has been derived for dSphs of the galaxy. By folding in kinematic information for 25 Andromeda dSphs, more than doubling the previous sample size, we find that a singular mass profile cannot be found to fit all of the observations well. Further, the best-fit dark matter density profile measured solely for the Milky Way dSphs is marginally discrepant with that of the Andromeda dSphs (at just beyond the 1σ level), where a profile with lower maximum circular velocity, and hence mass, is preferred. The agreement is significantly better when three extreme Andromeda outliers, And XIX, XXI, and XXV, all of which have large half-light radii (≳ 600 pc) and low-velocity dispersions (σv < 5 km s–1), are omitted from the sample. We argue that the unusual properties of these outliers are likely caused by tidal interactions with the host galaxy. [ABSTRACT FROM AUTHOR]

We present a homogeneous kinematic analysis of red giant branch stars within 18 of the 28 Andromeda dwarf spheroidal (dSph) galaxies, obtained using the Keck I/LRIS and Keck II/DEIMOS spectrographs. Based on their g - i colors (taken with the CFHT/MegaCam imager), physical positions on the sky, and radial velocities, we assign probabilities of dSph membership to each observed star. Using this information, the velocity dispersions, central masses, and central densities of the dark matter halos are calculated for these objects, and compared with the properties of the MilkyWay dSph population.We also measure the average metallicity ([Fe/H]) from the co-added spectra of member stars for each M31 dSph and find that they are consistent with the trend of decreasing [Fe/H] with luminosity observed in the Milky Way population. We find that three of our studied M31 dSphs appear as significant outliers in terms of their central velocity dispersion, And XIX, XXI, and XXV, all of which have large half-light radii (≳700 pc) and low velocity dispersions (σv < 5kms-1). In addition, And XXV has a mass-to-light ratio within its half-light radius of just [M/Llhalf = 10.3+7.0 -6.7, making it consistent with a simple stellar system with no appreciable dark matter component within its 1σ uncertainties. We suggest that the structure of the dark matter halos of these outliers have been significantly altered by tides. [ABSTRACT FROM AUTHOR]