Andromeda XXI -- a dwarf galaxy in a low density dark matter halo

Abstract

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 $v_r=-363.4\pm 1.0{\mathrm{kms}}^{-1}$ and a velocity dispersion of ${\sigma }_v=6.1_{-0.9}^{+1.0}{\mathrm{kms}}^{-1}$, consistent with previous work and within $1\sigma$ of predictions made within the modified Newtonian dynamics framework. We also measure the metallicity of our member stars from their spectra, finding a mean value of $[Fe/H]=-1.7\pm 0.1$~dex. We model the dark matter density profile of And~XXI using an improved version of \GravSphere, finding a central density of ${\rho }_{\mathrm{DM}}(150pc)=2.7_{-1.7}^{+2.7}\times 10^7{\mathrm{M}}_{\odot }\mathrm{kp}{\mathrm{c}}^{-3}$ at 68\% confidence, and a density at two half light radii of ${\rho }_{\mathrm{DM}}(1.75kpc)=0.9_{-0.2}^{+0.3}\times 10^5{\mathrm{M}}_{\odot }\mathrm{kp}{\mathrm{c}}^{-3}$ at 68\% confidence. These are both a factor $\sim 3-5$ 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 $>95\%$ of its mass), or if it inhabits a low concentration halo on a plunging orbit that experienced repeated tidal shocks.

Accepted to MNRAS, 17 pages, 12 figures

References in corpus (33)

• Array Programming with NumPy
• The Dartmouth Stellar Evolution Database
• Too big to fail? The puzzling darkness of massive Milky Way subhaloes
• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• The Tidal Evolution of Local Group Dwarf Spheroidals
• Velocity Dispersion Profiles of Seven Dwarf Spheroidal Galaxies
• A mass-dependent density profile for dark matter haloes including the influence of galaxy formation
• Dark Matter Substructure in Numerical Simulations: A Tale of Discreteness Noise, Runaway Instabilities, and Artificial Disruption
• Does the Fornax dwarf spheroidal have a central cusp or core?
• The NIR Ca II triplet at low metallicity - Searching for extremely low-metallicity stars in classical dwarf galaxies
• The stellar mass-halo mass relation of isolated field dwarfs: a critical test of $\Lambda$CDM at the edge of galaxy formation
• The PAndAS view of the Andromeda satellite system - II. Detailed properties of 23 M31 dwarf spheroidal galaxies
• A trio of new Local Group galaxies with extreme properties
• A kinematically selected, metal-poor stellar halo in the outskirts of M31
• On the formation of dwarf galaxies and stellar halos
• Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile
• A New Method for Isolating M31 Red Giant Stars: The Discovery of Stars out to a Radial Distance of 165 Kiloparsecs
• Andromeda Dwarfs in Light of MOND
• 3D motions in the Sculptor dwarf galaxy as a glimpse of a new era
• The effect of a disc on the population of cuspy and cored dark matter substructures in Milky Way-like galaxies
• EDGE: Two routes to dark matter core formation in ultra-faint dwarfs
• A detailed study of Andromeda XIX, an extreme local analogue of ultra diffuse galaxies
• Metallicity Evolution of the Six Most Luminous M31 Dwarf Satellites
• Spectroscopy of the three distant Andromedan satellites Cassiopeia III, Lacerta I, and Perseus I
• Breaking Beta: A comparison of mass modelling methods for spherical systems
• Comparing the Quenching Times of Faint M31 and Milky Way Satellite Galaxies
• Dynamical evidence for a strong tidal interaction between the Milky Way and its satellite, Leo V
• Global Properties of M31's Stellar Halo from the SPLASH Survey: III. Measuring the Stellar Velocity Dispersion Profile
• A low pre-infall mass for the Carina dwarf galaxy from disequilibrium modelling
• Kinematics of the Tucana Dwarf Galaxy: An Unusually Dense Dwarf in the Local Group
• N-body simulations of the Carina dSph in MOND
• Elemental abundances in M31: [Fe/H] and [α/Fe] in M31 Dwarf Galaxies Using Coadded Spectra
• Near-Gaussian distributions for modelling discrete stellar velocity data with heteroskedastic uncertainties

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