Galactic substructure traced by RR Lyraes in SDSS Stripe 82

TL;DR

This study uses RR Lyrae stars from SDSS Stripe 82 to map Galactic halo substructures, revealing known features and discovering a new overdensity at 100 kpc, supporting the idea of a debris-dominated halo.

Contribution

It identifies a previously unknown substructure, the Pisces Overdensity, and characterizes the halo's density profile with a broken power law.

Findings

Discovery of the Pisces Overdensity at ~100 kpc.

The halo's density profile fits a broken power law.

Most RR Lyrae stars are associated with known substructures.

Abstract

Using a sample of 407 RR Lyrae stars extracted from SDSS Stripe 82, we study the degree of substructure in the Galactic halo. We identify overdensities associated with the known substructures of the Hercules-Aquila Cloud and the Sagittarius Stream, and find a further previously-unknown substructure, the Pisces Overdensity, at ~100 kpc from the Sun. Together, the three substructures account for ~80% of our RR Lyrae sample. We also study the density distribution of RR Lyraes in the halo and find that the profile is best fit by a broken power law with an inner slope of -2.4 and a break radius of ~25 kpc, consistent with previous studies. We conclude that the halo is predominantly made up of the debris from in-falling satellites, with little or no underlying smooth component.