Identifying Star Streams in the Milky Way Halo

TL;DR

This paper introduces statistical methods combining spatial and radial velocity data to detect and analyze star streams in the Milky Way halo, successfully identifying the Sagittarius stream and estimating its contribution.

Contribution

The paper presents novel statistical techniques that jointly analyze spatial and velocity data to improve detection of star streams in the galactic halo.

Findings

Detected Sagittarius stream with high significance

Sagittarius stream makes up 10-17% of halo stars in the sample

Variation in stellar populations along the stream

Abstract

We develop statistical methods for identifying star streams in the halo of the Milky Way galaxy that exploit observed spatial and radial velocity distributions. Within a great circle, departures of the observed spatial distribution from random provide a measure of the likelihood of a potential star stream. Comparisons between the radial velocity distribution within a great circle and the radial velocity distribution of the entire sample also measure the statistical significance of potential streams. The radial velocities enable construction of a more powerful joint statistical test for identifying star streams in the Milky Way halo. Applying our method to halo stars in the Hypervelocity Star (HVS) survey, we detect the Sagittarius stream at high significance. Great circle counts and comparisons with theoretical models suggest that the Sagittarius stream comprises 10% to 17% of the halo stars in the HVS sample. The population of blue stragglers and blue horizontal branch stars varies along the stream and is a potential probe of the distribution of stellar populations in the Sagittarius dwarf galaxy prior to disruption.