Astro Lunch

The Shapes and Alignments of Dwarf Galaxies

There are over 30 dwarf spheroidal galaxies surrounding the Milky Way,
normally divided into the comparatively bright classical population
and the more diffuse & irregular ultrafaints. These objects are
interesting because they are highly dark matter dominated and because
their origins remain obscure.  Although traditionally modelled as
spherical, we argue that their intrinsic shape is important, both for
assessing any dark matter signal and for understanding their alignment
and kinematics. Once a triaxial body is embedded in the Milky Way's
tidal field, then its intrinsic shape couples its apparent ellipticity
on the sky to its orbital phase on its journey around the Milky Way.

The talk will discuss the dark matter annihilation signal from
flattened dwarfs, with emphasis on the reported signal from Reticulum
II. We will analyze the claims of preferred planes and orientations
amongst the dwarf populations of both the Milky Way and M31. We will
discuss formation scenarios for two unusual dwarf galaxies in some
detail. The first is 'the feeble giant' or the anomalously large and
cold dwarf galaxy Crater II. The second is Sculptor, with its
peculiar, highly radially anisotropic kinematics. Finally, the Gaia
satellite will revolutionise this area in 2 months time, with accurate
proper motions for most of these objects, and we assess how the
landscape will look by the end of the year.