The Sagittarius Streams in the Southern Galactic Hemisphere

TL;DR

This paper analyzes the structure and stellar populations of the Sagittarius stream in the Southern Galactic hemisphere, revealing a bifurcated structure with distinct properties and interactions with other streams like Cetus.

Contribution

It provides detailed morphological and stellar population analysis of the Southern Sagittarius stream, identifying a bifurcation and its relation to other halo streams.

Findings

Identification of a fainter, more metal-poor stream parallel to Sagittarius

Evidence of a bifurcated structure similar to the Northern bifurcation

Overlap and interaction with the Cetus stream in the South Galactic Cap

Abstract

The structure of the Sagittarius stream in the Southern Galactic hemisphere is analysed with the Sloan Digital Sky Survey Data Release 8. Parallel to the Sagittarius tidal track, but ~ 10deg away, there is another fainter and more metal-poor stream. We provide evidence that the two streams follow similar distance gradients but have distinct morphological properties and stellar populations. The brighter stream is broader, contains more metal-rich stars and has a richer colour-magnitude diagram with multiple turn-offs and a prominent red clump as compared to the fainter stream. Based on the structural properties and the stellar population mix, the stream configuration is similar to the Northern "bifurcation". In the region of the South Galactic Cap, there is overlapping tidal debris from the Cetus Stream, which crosses the Sagittarius stream. Using both photometric and spectroscopic data, we show that the blue straggler population belongs mainly to Sagittarius and the blue horizontal branch stars belong mainly to the Cetus stream in this confused location in the halo.