The massive halos of spiral galaxies

Dennis F Zaritsky, Simon D M White

Research output: Contribution to journalArticle

116 Citations (Scopus)

Abstract

We use the sample of satellite galaxies presented by Zaritsky et al. (1993) to demonstrate the existence of extended massive dark halos around spiral galaxies. Isolated spirals with rotation velocities near 250 km s-1 have a typical halo mass within 200 kpc of 1.5-2.6 × 1012 M (90% confidence range for H0 = 75 km s-1 Mpc-1). This result is most easily derived using standard mass estimator techniques, but such techniques do not account for the strong observational selection effects in the sample, nor for the extended mass distributions that the data imply. These complications can be addressed using scale-free models similar to those previously employed to study binary galaxies. When satellite velocities are assumed isotropic, both methods imply massive and extended halos. However, the derived masses depend sensitively on the assumed shape of satellite orbits. Furthermore, both methods ignore the fact that many of the satellites in the sample have orbital periods comparable to the Hubble time. The orbital phases of such satellites cannot be random, and their distribution in radius cannot be freely adjusted; rather these properties reflect ongoing infall onto the outer halos of their primaries. We use detailed dynamical models for halo formation to evaluate these problems, and we devise a maximum likelihood technique for estimating the parameters of such models from the data. The most strongly constrained parameter is the mass within 200-300 kpc, giving the confidence limits quoted above. The eccentricity, e, of satellite orbits is also strongly constrained, 0.50 < e < 0.88 at 90% confidence, implying a near-isotropic distribution of satellite velocities. The cosmic density parameter in the vicinity of our isolated halos exceeds 0.13 at 90% confidence, with preferred values exceeding 0.3.

Original languageEnglish (US)
Pages (from-to)599-610
Number of pages12
JournalAstrophysical Journal
Volume435
Issue number2
StatePublished - Nov 10 1994

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spiral galaxies
halos
confidence
satellite orbits
galaxies
orbitals
confidence limits
mass distribution
eccentricity
estimators
estimating
radii
distribution
parameter

Keywords

  • Galaxies: kinematics and dynamics
  • Galaxies: spiral
  • Galaxies: structure

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Zaritsky, D. F., & White, S. D. M. (1994). The massive halos of spiral galaxies. Astrophysical Journal, 435(2), 599-610.

The massive halos of spiral galaxies. / Zaritsky, Dennis F; White, Simon D M.

In: Astrophysical Journal, Vol. 435, No. 2, 10.11.1994, p. 599-610.

Research output: Contribution to journalArticle

Zaritsky, DF & White, SDM 1994, 'The massive halos of spiral galaxies', Astrophysical Journal, vol. 435, no. 2, pp. 599-610.
Zaritsky, Dennis F ; White, Simon D M. / The massive halos of spiral galaxies. In: Astrophysical Journal. 1994 ; Vol. 435, No. 2. pp. 599-610.
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