Probing the 2D kinematic structure of early-type galaxies out to three effective radii

Robert N. Proctor, Duncan A. Forbes, Aaron J. Romanowsky, Jean P. Brodie, Jay Strader, Max Spolaor, J. Trevor Mendel, Lee Spitler

Research output: Contribution to journalArticlepeer-review

66 Citations (Scopus)


We detail an innovative new technique for measuring the two-dimensional (2D) velocity moments (rotation velocity, velocity dispersion and Gauss-Hermite coefficients h3 and h4) of the stellar populations of galaxy haloes using spectra from Keck DEIMOS (Deep Imaging Multi-Object Spectrograph) multi-object spectroscopic observations. The data are used to reconstruct 2D rotation velocity maps. Here we present data for five nearby early-type galaxies to ∼three effective radii. We provide significant insights into the global kinematic structure of these galaxies, and challenge the accepted morphological classification in several cases. We show that between one and three effective radii the velocity dispersion declines very slowly, if at all, in all five galaxies. For the two galaxies with velocity dispersion profiles available from planetary nebulae data we find very good agreement with our stellar profiles. We find a variety of rotation profiles beyond one effective radius, i.e. rotation speed remaining constant, decreasing and increasing with radius. These results are of particular importance to studies which attempt to classify galaxies by their kinematic structure within one effective radius, such as the recent definition of fast- and slow-rotator classes by the Spectrographic Areal Unit for Research on Optical Nebulae project. Our data suggest that the rotator class may change when larger galactocentric radii are probed. This has important implications for dynamical modelling of early-type galaxies. The data from this study are available on-line.

Original languageEnglish
Pages (from-to)91-108
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - Sep 2009
Externally publishedYes


  • Galaxies: General
  • Galaxies: Kinematics and dynamics
  • Galaxies: Structure
  • Stellar dynamics
  • Techniques: Spectroscopic

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