Faint stars in the Ursa Minor dwarf spheroidal galaxy: implications for the low-mass stellar initial mass function at high redshift

摘要: The stellar initial mass function at high redshift is an important defining property of the first systems to form and may also play a role in various dark matter problems. We here determine faint luminosity apparently dark-matter-dominated external galaxy which stars formed redshift. Ursa Minor dwarf spheroidal system with particularly simple population-all being old metal-poor-similar that classical halo globular cluster. A direct comparison functions UMi dSph similar metallicity, clusters equivalent presented here, based on deep HST WFPC2 STIS imaging data. find these are indistinguishable, down corresponding to0.3 M-.. Our results show low-mass IMF for very invariant across environments as diverse those extremely low-surface-brightness, dark-matter-free, high-density cluster within Milky Way.