The orbital distribution of satellite galaxies

Stéphane Herbert-Fort, Dennis Zaritsky, Yeun Jin Kim, Jeremy Bailin, James E. Taylor

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


We measure the distribution of velocities for prograde and retrograde satellite galaxies using a combination of published data and new observations for 78 satellites of 63 extremely isolated disc galaxies (169 satellites total). We find that the velocity distribution is non-Gaussian (>99.9 per cent confidence), but that it can be described as the sum of two Gaussians, one of which is broad (σ = 176 ± 15 km s-1), has a mean prograde velocity of 86 ± 30 km s-1, and contains ∼55 per cent of the satellites, while the other is slightly retrograde with a mean velocity of -21 ± 22 km s-1 and σ = 74 ± 18 km s-1 and contains ∼45 per cent of the satellites. Both of these components are present over all projected radii and found in the sample regardless of cuts on primary inclination or satellite disc angle. The double-Gaussian shape, however, becomes more pronounced among satellites of more luminous primaries. We remove the potential dependence of satellite velocity on primary luminosity using the Tully-Fisher relation and still find the velocity distribution to be asymmetric and even more significantly non-Gaussian. The asymmetric velocity distribution demonstrates a connection between the inner, visible disc galaxy, and the kinematics of the outer, dark halo. The reach of this connection, extending even beyond the virial radii, suggests that it is imprinted by the satellite infall pattern and large-scale effects, rather than by higher level dynamical processes in the formation of the central galaxy or late-term evolution of the satellites.

Original languageEnglish (US)
Pages (from-to)803-813
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Feb 2008


  • Dark matter
  • Galaxies: evolution
  • Galaxies: haloes
  • Galaxies: structure

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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