Ewa L. Lokas, Steven R. Majewski, Stelios Kazantzidis, Lucio Mayer, Jeffrey L. Carlin, David L. Nidever, Leonidas A. Moustakas
We study the shapes of Milky Way satellites in the context of the tidal
stirring scenario for the formation of dwarf spheroidal galaxies. The standard
procedures used to measure shapes involve smoothing and binning of data and
thus may not be sufficient to detect subtle structural properties like bars.
Taking advantage of the fact that in nearby dwarfs photometry of individual
stars is available we introduce discrete measures of shape based on the
two-dimensional inertia tensor and the Fourier bar mode. We apply these
measures of shape first to a variety of simulated dwarf galaxies formed via
tidal stirring of disks embedded in dark matter halos and orbiting the Milky
Way. In addition to strong mass loss and randomization of stellar orbits, the
disks undergo morphological transformation which typically involves the
formation of a triaxial bar after the first pericenter passage. These tidally
induced bars persist for a few Gyr before being shortened towards a more
spherical shape if the tidal force is strong enough. We test this prediction by
measuring in a similar way the shape of nearby dwarf galaxies, satellites of
the Milky Way. We detect inner bars in Ursa Minor, Sagittarius, LMC and
possibly Carina. In addition, six out of eleven studied dwarfs show elongated
stellar distributions in the outer parts which may signify transition to the
tidal tails. We thus find the shapes of Milky Way satellites to be consistent
with the predictions of the tidal stirring model.
View original:
http://arxiv.org/abs/1112.5336
No comments:
Post a Comment