|
Résumé d'un journal-club
Date
| Sujet
| Présenté par
|
10 septembre 2009 | Modelling
mass indepedent of anisotropy: connecting observations to
simulations
Mass profile determinations for dispersion
supported galaxies from line-of-sight velocities are subject to large
uncertainties associated with the unknown stellar velocity
anisotropy. We demonstrate both analytically and with available
kinematic data (for systems spanning over seven decades in mass) that
the mass-anisotropy degeneracy is effectively eliminated at a
characteristic radius that is close to the 3D deprojected half-light
radius of the stars. This allows a simple, yet accurate formula to
describe the total half-light masses of all hot systems, including
dwarf spheroidal galaxies (dSphs), based on directly observable
parameters: M_1/2 = 4 sigma_LOS^2 R_half G, where R_half is the 2D
projected half-light radius and sigma_LOS is the
line-of-sight velocity dispersion. The fact that masses are
well-constrained within a characteristic stellar radius has allowed
our group to perform systematic, accurate mass determinations for
Milky Way dSphs and to conclude that they all have a common mass scale
of approximately 10^7 M_\odot within 300 pc of their centers. We
extend this work to the satellite population of Andromeda using
Keck/DEIMOS spectroscopy of individual stars. We find that the
Andromeda dSphs are also consistent with sharing a common mass, but
that it is offset from the scale of the Milky Way dSphs by a factor of
nearly 2. With this, we will discuss implications for galaxy formation
scenarios. Lastly, we will discuss what advances can be made by
utilizing proper motion measurements of individual stars in these
dSphs. | Joe
Wolf
Center for Cosmology, Univ. California, Irvine
|
Image : Champ profond D1 du relevé Legacy du Télescope Canada-France-Hawaï (CFHTLS)
Centre de traitement des données TERAPIX (CNRS/INSU - IAP - CEA)
|