Near-Field Cosmology with Horizontal Branch and RR Lyrae Stars

TL;DR

This paper discusses how horizontal branch and RR Lyrae stars provide insights into the formation of the Galactic halo, challenging the idea that it formed solely from accreted dwarf galaxy fragments.

Contribution

It offers a cosmological perspective on the role of these stars in understanding the Milky Way's formation, emphasizing their properties in globular clusters.

Findings

Galactic halo globular clusters likely did not form from dwarf galaxy fragments.

RR Lyrae properties in the halo differ from those in dwarf satellites.

Supports a different formation scenario for the Galactic halo.

Abstract

The importance of horizontal branch and RR Lyrae stars is discussed in the context of cosmological arguments for the formation of the Galactic halo and its satellite dwarf galaxies. It is shown, in particular, that the Galactic halo globular cluster system cannot have formed from the accretion of ``protogalactic fragments'' resembling the very early counterparts of the present-day dwarf satellite galaxies of the Milky Way, or else its RR Lyrae properties would be very different from what is currently observed.