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| Paper: |
The Dark Halo in NGC 821 |
| Volume: |
352, New Horizons in Astronomy: Frank N. Bash Symposium 2005 |
| Page: |
241 |
| Authors: |
Forestell, A.D.; Gebhardt, K. |
| Abstract: |
The study of elliptical galaxy dark halos at large radii is important because it is the region where dark matter is thought to dominate the galaxy mass and can therefore provide the best constraints on observed dark halo properties. We present axisymmetric orbit-superposition models of the dark halo in the elliptical galaxy NGC 821 using line-of-sight velocity distributions obtained to ∼100″ (over 2 effective radii) with long-slit spectroscopy from the Hobby- Eberly Telescope. We fit models with a range of dark halo density profiles and find that a power-law dark halo with a constant density of 0.0105 MSolar/pc3 is the best-fitting model ruling out both the no dark halo and the Navarro, Frenk, & White (1996; NFW) models at a greater than 3σ confidence level. We show the internal moments σr, σθ, and σφ and find that the model with no dark halo is radially anisotropic at small radii and tangentially anisotropic at large radii while the best-fit halo models are slightly radially anisotropic at all radii. The dark halo we find is inconsistent with previous claims of little to no dark matter halo in this galaxy based on planetary nebula measurements. |
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