Internal kinematics of the Leo II dwarf spheroidal galaxy

Steven S. Vogt, Mario Mateo, Edward W Olszewski, Michael J. Keane

Research output: Contribution to journalArticle

76 Citations (Scopus)

Abstract

We have obtained radial velocities of 31 red giants in the Leo II dwarf spheroidal (dSph) galaxy using the HIRES echelle spectrograph of the Keck 10 m telescope. These stars were selected using CCD photometry obtained with the Palomar 1.5 m telescope. The radial velocity errors were determined from repeat measurements of Leo II giants and faint radial velocity standards; the average error for the Leo II giants is 2.4 km s-1. The systemic velocity of Leo II is 76.0±1.3 km s-1, and the velocity dispersion is 6.7±1.1 km s-1. Adopting the standard assumptions (mass follows light, isotropy, and equilibrium) we derive a "global" V-band mass-to-light ratio (Mtot/Ltot) = 11.1±3.8, and a central value (ρ0/I0) = 11.6±3.2 (both in solar units). These values are larger than the M/L ratios measured for "local" stellar populations (star clusters or the solar neighborhood). Monte Carlo simulations show that a large population of binaries probably has not inflated a small intrinsic velocity dispersion to the observed value. A model-independent lower limit of the central mass density of Leo II yields ρ0,min=0.074M pc-3, larger than the central luminous mass density in Leo II for (M/L)1um=2.0. This demands an extensive dark halo in the outer regions of the galaxy to account for the observed dispersion. We conclude that Leo II contains a significant dark matter component. The total mass of the dark halo is 0.9 × 107 M⊙, consistent with the masses inferred in all well-studied dSph galaxies. Because it is remote from the Galaxy, tides cannot plausibly affect the velocity dispersion of Leo II. However, we cannot use these results to rule out the possibility that tides may influence the kinematics of other dSph galaxies found closer to the Milky Way.

Original languageEnglish (US)
Pages (from-to)151-163
Number of pages13
JournalAstronomical Journal
Volume109
Issue number1
StatePublished - Jan 1995

Fingerprint

dwarf galaxies
kinematics
radial velocity
tides
halos
telescopes
velocity errors
galaxies
mass to light ratios
solar neighborhood
tide
isotropy
star clusters
extremely high frequencies
spectrographs
photometry
charge coupled devices
dark matter
stars
simulation

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Vogt, S. S., Mateo, M., Olszewski, E. W., & Keane, M. J. (1995). Internal kinematics of the Leo II dwarf spheroidal galaxy. Astronomical Journal, 109(1), 151-163.

Internal kinematics of the Leo II dwarf spheroidal galaxy. / Vogt, Steven S.; Mateo, Mario; Olszewski, Edward W; Keane, Michael J.

In: Astronomical Journal, Vol. 109, No. 1, 01.1995, p. 151-163.

Research output: Contribution to journalArticle

Vogt, SS, Mateo, M, Olszewski, EW & Keane, MJ 1995, 'Internal kinematics of the Leo II dwarf spheroidal galaxy', Astronomical Journal, vol. 109, no. 1, pp. 151-163.
Vogt, Steven S. ; Mateo, Mario ; Olszewski, Edward W ; Keane, Michael J. / Internal kinematics of the Leo II dwarf spheroidal galaxy. In: Astronomical Journal. 1995 ; Vol. 109, No. 1. pp. 151-163.
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