Mapping the Galactic Halo with SDSS, LINEAR and PTF RR Lyrae Stars

TL;DR

This study maps the Galactic halo using RR Lyrae stars from SDSS, revealing known and new substructures, a steepening density profile beyond 30 kpc, and metallicity estimates for tidal streams, advancing our understanding of halo composition and structure.

Contribution

The paper provides a detailed 2D map of the Galactic halo up to 100 kpc, identifies new substructures, and introduces a novel photometric metallicity method combining RR Lyrae and main sequence stars.

Findings

Halo density profile steepens beyond 30 kpc.

Identification of new halo substructures like Pisces stream.

Median metallicity of Sagittarius stream is [Fe/H]=-1.2 dex.

Abstract

We present an analysis of Galactic halo structure and substructure traced by ~500 RR Lyrae stars in the SDSS stripe 82 region. The main result of this study is a 2D map of the Galactic halo that reaches distances of 100 kpc and traces previously known and new halo substructures, such as the Sagittarius and Pisces tidal streams. We also present strong direct evidence, based on both RR Lyrae and main sequence stars, that the halo stellar number density profile significantly steepens beyond 30 kpc from the Galactic center. Using a novel photometric metallicity method that simultaneously combines data for RR Lyrae and main sequence stars, we show that the median metallicity of the Sagittarius trailing stream in the SDSS stripe 82 region is [Fe/H]}=-1.2 +- 0.1 dex. In addition to these results, we will present ongoing work on a 3D map of the Galactic halo constructed using a sample of ~4000 RR Lyrae stars that covers 8500 deg^2 of northern sky and probes up to 30 kpc from the Sun.