The Structure of the Sagittarius Stellar Stream as Traced by Blue Horizontal Branch Stars

TL;DR

This study uses Sloan Digital Sky Survey data to analyze the Sagittarius stellar stream through blue horizontal branch stars, revealing its structure, extent, and velocity characteristics, and providing a refined view of its tidal debris.

Contribution

It introduces a photometry-based method to identify BHB stars with high purity and applies it to map the Sagittarius stream's structure and kinematics in unprecedented detail.

Findings

Identified a possible extension of the trailing arm at 60-80 kpc.

Estimated the line-of-sight thickness of the leading arm to be ~3 kpc.

Measured the velocity dispersion of the leading arm as 37 km/s.

Abstract

We use a sample of blue horizontal branch (BHB) stars from the Sloan Digital Sky Survey Data Release 7 to explore the structure of the tidal tails from the Sagittarius Dwarf Galaxy. We use a method yielding BHB star candidates with up to ~70% purity from photometry alone. The resulting sample has a distance precision of roughly 5% and can probe distances in excess of 100 kpc. Using this sample, we identify a possible extension to the trailing arm at distances of 60-80 kpc from the Sun with an estimated significance of at least 3.8 sigma. Current models predict that a distant `returning' segment of the debris stream should exist, but place it substantially closer to the Sun where no debris is observed in our data. Exploiting the distance precision of our tracers, we estimate the mean line-of-sight thickness of the leading arm to be ~3 kpc, and show that the two `bifurcated' branches of the debris stream differ by only 1-2 kpc in distance. With a spectroscopic very pure BHB star subsample, we estimate the velocity dispersion in the leading arm, 37 km s^-1, which is in reasonable agreement with models of Sgr disruption. We finally present a sample of high-probability Sgr BHB stars in the leading arm of Sgr, selected to have distances and velocities consistent with Sgr membership, to allow further study.