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Multiple chemodynamic stellar populations of the Ursa Minor dwarf spheroidal galaxy

From National Research Council Canada

DOIResolve DOI: https://doi.org/10.1093/mnras/staa1419
AuthorSearch for: ORCID identifier: https://orcid.org/0000-0002-6021-8760; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: 1; Search for: ; Search for:
Affiliation
  1. National Research Council of Canada. Herzberg Astronomy and Astrophysics
FunderSearch for: UCI; Search for: NSF; Search for: California Institute of Technology; Search for: FONDECYT; Search for: W.M. Keck Foundation
FormatText, Article
Subjectgalaxies: evolution; galaxies: kinematics and dynamics; Local Group; cosmology: dark matter; galaxies: individual: Ursa Minor dSph
Abstract
We present a Bayesian method to identify multiple (chemodynamic) stellar populations in dwarf spheroidal galaxies (dSphs) using velocity, metallicity, and positional stellar data without the assumption of spherical symmetry. We apply this method to a new Keck/Deep Imaging Multi-Object Spectrograph (DEIMOS) spectroscopic survey of the Ursa Minor (UMi) dSph. We identify 892 likely members, making this the largest UMi sample with line-of-sight velocity and metallicity measurements. Our Bayesian method detects two distinct chemodynamic populations with high significance (in logarithmic Bayes factor, ln B ∼ 33). The metal-rich ([Fe/H] = −2.05 ± 0.03) population is kinematically colder (radial velocity dispersion of σv=4.9⁺⁰.⁸₋₁.₀kms⁻¹) and more centrally concentrated than the metal-poor (⁠[Fe/H]=−2.29⁺⁰.⁰⁵−₀.₀₆⁠) and kinematically hotter population (⁠σv=11.5⁺⁰.⁹−₀.₈kms⁻¹⁠). Furthermore, we apply the same analysis to an independent Multiple Mirror Telescope (MMT)/Hectochelle data set and confirm the existence of two chemodynamic populations in UMi. In both data sets, the metal-rich population is significantly flattened (ϵ = 0.75 ± 0.03) and the metal-poor population is closer to spherical (⁠ϵ=0.33⁺⁰.¹²−₀.₀₉⁠). Despite the presence of two populations, we are able to robustly estimate the slope of the dynamical mass profile. We found hints for prolate rotation of order ∼2kms⁻¹ in the MMT data set, but further observations are required to verify this. The flattened metal-rich population invalidates assumptions built into simple dynamical mass estimators, so we computed new astrophysical dark matter annihilation (J) and decay profiles based on the rounder, hotter metal-poor population and inferred log10(J(0∘.5)/GeV²cm−⁵)≈19.1 for the Keck data set. Our results paint a more complex picture of the evolution of UMi than previously discussed.
Publication date
PublisherOxford
Royal Astronomical Society
In
  • Monthly Notices of the Royal Astronomical Society 495, no. 3 (22 May 2020): 3022–3040.
LanguageEnglish
Peer reviewedYes
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Record identifier9ed1b715-cc35-4816-bc42-931ba3067686
Record created2022-05-16
Record modified2022-05-16
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