Galaxy formation and evolution

Abstract:

Cappellari (2008) presented a flexible and efficient method to model the stellar kinematics of anisotropic axisymmetric and spherical stellar systems. The spherical formalism could be used to model the line-of-sight velocity second moments allowing for essentially arbitrary radial variations in the anisotropy and general luminous and total density profiles. Here we generalize the spherical formalism by providing the expressions for all three components of the projected second moments, including the two proper motion components. A reference implementation is now included in the public JAM package available at http://purl.org/cappellari/software.

Abstract:

We study the total mass-density profile for a sample of 14 fast-rotator early-type galaxies (stellar masses ). We combine observations from the SLUGGS and ATLAS surveys to map out the stellar kinematics in two dimensions, out to a median radius for the sample of four half-light radii Re (or 10 kpc) and a maximum radius of 2.0-6.2 Re (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 from Re/10 to at least 4Re, the largest average deviation being 11%. The average logarithmic slope is with observed rms scatter of just . This scatter out to large radii, where dark matter dominates, is as small as previously reported by lensing studies around r ≈ Re/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.