John Magorrian

Abstract:

This is the first of a series of papers dedicated to unveiling the mass composition and dynamical structure of a sample of flattened early-type galaxies in the Coma cluster. We describe our modifications to the Schwarzschild code of Richstone et al. Applying a Voronoi tessellation in the surface of section, we are able to assign accurate phase-space volumes to individual orbits and to reconstruct the full three-integral phase-space distribution function (DF) of any axisymmetric orbit library. Two types of tests have been performed to check the accuracy with which DFs can be represented by appropriate orbit libraries. First, by mapping DFs of spherical γ-models and flattened Plummer models onto the library, we show that the resulting line-of-sight velocity distributions and internal velocity moments of the library match those derived directly from the DF to a precision better than that of present-day observational errors. Secondly, by fitting libraries to the projected kinematics of the same DFs, we show that the DF reconstructed from the fitted library matches the input DF to a rms of about 15 per cent over a region in phase space covering 90 per cent of the mass of the library. The accuracy achieved allows us to implement effective entropy-based regularization to fit real, noisy and spatially incomplete data.

Abstract:

We present preliminary results from spectroscopic observations of a sample of 11 low surface brightness galaxies (LSB). We measured the stellar and gaseous kinematics along their major and minor axes. Such information will allow us to accurately investigate the dark matter (DM) content within their optical regions, providing further constraints on the predictions of standard CDM models. Although dynamical modeling is still in progress, our observations already show that the derived stellar kinematics is more regular than the ionized gas one, which often shows evidence for non-circular and asymmetric motions.