Crater 2: An Extremely Cold Dark Matter Halo

Nelson Caldwell, Matthew G. Walker, Mario Mateo, Edward W Olszewski, Sergey Koposov, Vasily Belokurov, Gabriel Torrealba, Alex Geringer-Sameth, Christian I. Johnson

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

We present results from MMT/Hectochelle spectroscopy of 390 red giant candidate stars along the line of sight to the recently discovered Galactic satellite Crater 2. Modeling the joint distribution of stellar positions, velocities, and metallicities as a mixture of Crater 2 and Galactic foreground populations, we identify ∼62 members of Crater 2, for which we resolve a line-of-sight velocity dispersion of = km s-1 and a mean velocity of = km s-1 (solar rest frame). We also resolve a metallicity dispersion of = dex and a mean of = dex that is 0.28 ±0.14 dex poorer than estimated from photometry. Despite Crater 2's relatively large size (projected halflight radius R h ∼ 1 kpc) and intermediate luminosity (M V ∼ -8), its velocity dispersion is the coldest that has been resolved for any dwarf galaxy. These properties make Crater 2 the most extreme low-density outlier in dynamical as well as structural scaling relations among the Milky Way's dwarf spheroidals. Even so, under assumptions of dynamical equilibrium and negligible contamination by unresolved binary stars, the observed velocity distribution implies a gravitationally dominant dark matter halo, with a dynamical mass of M o and a mass-to-light ratio of enclosed within a radius of ∼1 kpc, where the equivalent circular velocity is km s-1.

Original languageEnglish (US)
Article number20
JournalAstrophysical Journal
Volume839
Issue number1
DOIs
StatePublished - Apr 10 2017

Fingerprint

craters
crater
halos
dark matter
line of sight
metallicity
red giant stars
mass to light ratios
radii
binary stars
dwarf galaxies
photometry
outlier
contamination
velocity distribution
luminosity
cold
scaling
spectroscopy
modeling

Keywords

  • galaxies: dwarf
  • galaxies: individual (Crater 2)
  • galaxies: kinematics and dynamics
  • Local Group
  • methods: data analysis
  • techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Caldwell, N., Walker, M. G., Mateo, M., Olszewski, E. W., Koposov, S., Belokurov, V., ... Johnson, C. I. (2017). Crater 2: An Extremely Cold Dark Matter Halo. Astrophysical Journal, 839(1), [20]. https://doi.org/10.3847/1538-4357/aa688e

Crater 2 : An Extremely Cold Dark Matter Halo. / Caldwell, Nelson; Walker, Matthew G.; Mateo, Mario; Olszewski, Edward W; Koposov, Sergey; Belokurov, Vasily; Torrealba, Gabriel; Geringer-Sameth, Alex; Johnson, Christian I.

In: Astrophysical Journal, Vol. 839, No. 1, 20, 10.04.2017.

Research output: Contribution to journalArticle

Caldwell, N, Walker, MG, Mateo, M, Olszewski, EW, Koposov, S, Belokurov, V, Torrealba, G, Geringer-Sameth, A & Johnson, CI 2017, 'Crater 2: An Extremely Cold Dark Matter Halo', Astrophysical Journal, vol. 839, no. 1, 20. https://doi.org/10.3847/1538-4357/aa688e
Caldwell N, Walker MG, Mateo M, Olszewski EW, Koposov S, Belokurov V et al. Crater 2: An Extremely Cold Dark Matter Halo. Astrophysical Journal. 2017 Apr 10;839(1). 20. https://doi.org/10.3847/1538-4357/aa688e
Caldwell, Nelson ; Walker, Matthew G. ; Mateo, Mario ; Olszewski, Edward W ; Koposov, Sergey ; Belokurov, Vasily ; Torrealba, Gabriel ; Geringer-Sameth, Alex ; Johnson, Christian I. / Crater 2 : An Extremely Cold Dark Matter Halo. In: Astrophysical Journal. 2017 ; Vol. 839, No. 1.
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