Small scatter and nearly isothermal mass profiles to four half-light radii from two-dimensional stellar dynamics of early-type galaxies
- Sub-department of Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom)
- University of California Observatories, 1156 High Street, Santa Cruz, CA 95064 (United States)
- Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia)
- Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)
- Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia)
We study the total mass–density profile for a sample of 14 fast-rotator early-type galaxies (stellar masses 10.2≲logM{sub ∗}/M{sub ⊙}≲11.7). We combine observations from the SLUGGS and ATLAS{sup 3D} surveys to map out the stellar kinematics in two dimensions, out to a median radius for the sample of four half-light radii R{sub e} (or 10 kpc) and a maximum radius of 2.0–6.2 R{sub e} (or 4–21 kpc). We use axisymmetric dynamical models based on the Jeans equations, which allow for a spatially varying anisotropy; employ quite general profiles for the dark halos; and, in particular, do not place any restrictions on the profile slope. This is made possible by the availability of spatially extended two-dimensional kinematics. We find that our relatively simple models provide a remarkably good description of the observed kinematics. The resulting total density profiles are well described by a nearly isothermal power law ρ{sub tot}(r)∝r{sup −γ} from R{sub e}/10 to at least 4R{sub e}, the largest average deviation being 11%. The average logarithmic slope is 〈γ〉=2.19±0.03 with observed rms scatter of just σ{sub γ}=0.11. This scatter out to large radii, where dark matter dominates, is as small as previously reported by lensing studies around r ≈ R{sub e}/2, where the stars dominate. Our bulge–halo conspiracy places much tighter constraints on galaxy formation models. It illustrates the power of two-dimensional stellar kinematics observations at large radii. It is now important to test the generality of our results for different galaxy types and larger samples.
- OSTI ID:
- 22868717
- Journal Information:
- Astrophysical Journal Letters, Vol. 804, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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