Wide Field Observations of the Ursa Minor dSph Galaxy

1 99 9 Wide Field Observations of the Ursa Minor dSph galaxy

1. Introduction The discovery that the Saggitarius dSph is dissolving into the Galactic halo (Ibata, Gilmore & Irwin 1994; Mateo et al 1998) has strengthened the idea that current accretion events could play an important role in the history of the Milky Way formation. Nevertheless, the argument that other dSph satellites can be tidally disrupted by the Milky Way is open to debate. It is thus ve...

THE IMF LONG AGO AND FAR AWAY: Faint Stars in the Ursa Minor dSph Galaxy

The dwarf spheroidal galaxy in Ursa Minor is apparently dark-matter dominated, and is of very low surface brightness, with total luminosity only equal to that of a globular cluster. Indeed its dominant stellar population is old and metal-poor, very similar to that of a classical halo globular cluster in the Milky Way Galaxy. However, the environment in which its stars formed was clearly differe...

New Limits on Sterile Neutrinos from Suzaku Observations of the Ursa Minor Dwarf Spheroidal Galaxy

We present results of our search for X-ray line emission associated with the radiative decay of the sterile neutrino, a well-motivated dark matter candidate, in Suzaku Observatory spectra of the Ursa Minor dwarf spheroidal galaxy. These data represent the first deep observation of one of these extreme mass-to-light systems and the first dedicated dark matter search using an X-ray telescope. No ...

A dynamical fossil in the Ursa Minor dwarf spheroidal galaxy

The nearby Ursa Minor dwarf spheroidal (UMi dSph) is one of the most dark matter dominated galaxies known, with a central mass to light ratio M/L ∼ 70. Somewhat anomalously, it appears to contain morphological substructure in the form of a second peak in the stellar number density. It is often argued that this substructure must be transient because it could not survive for the > 10 Gyr age of t...

The Low - Mass Stellar IMF at High Redshift : Faint Starsin the Ursa Minor Dwarf Spheroidal Galaxy