Claudia Greco
INAF-Osservatorio Astronomico di Bologna

Looking for the Building Blocks of the Galactic Halo: Variable stars in Fornax and Bootes dwarfs and in NGC 2419

Abstract

In hierarchical models of galaxy formation, the halo of the Milky Way (MW) has been assembled, at least in part, through the accretion of protogalactic fragments partially resembling the present-day dwarf spheroidal (dSph) satellites of the MW. The RR Lyrae stars, belonging to the old population (t > 10 Gyr), eyewitnessed the epoch of the halo formation, and thus hold a crucial role to identify the MW satellites that may have contributed to building the Galactic halo. In the talk, we focus on the identification of the possible ``building blocks'' of the Galactic halo, by investigating the RR Lyrae properties of a number of different stellar systems starting from relatively undisturbed dwarf galaxies (the Fornax dSph), through distorted and tidally disrupting ones (the Bootes dSph), to possible final relics of the disruption process (the Galactic globular cluster NGC 2419). We are addressing the question of whether the properties of the RR Lyrae stars in these systems conform to the ones observed in the MW. If they do not, the Galaxy's halo cannot have been assembled by dSph-like protogalactic fragments resembling these present-day dSph companions of the MW.