The Galactic Anticenter Stellar Stream

TL;DR

This paper detects and characterizes the Galactic Anticenter Stellar Stream using 2MASS M giant stars, revealing its extent, metallicity, and suggesting it is a localized merging dwarf galaxy rather than a uniform ring.

Contribution

Developed a new method to trace stellar streams from distance PDFs, revealing the structure's properties and challenging previous interpretations.

Findings

Detected the stream at 18±2 kpc distance.

Found the stream contains higher metallicity populations.

Suggests the structure is a merging dwarf galaxy, not a ring.

Abstract

The recently discovered, ring-like structure just outside the Galactic disk in Monoceros is detected and traced among 2MASS M giant stars. We have developed a method to recover the signature of this structure from the distance probability density function of stars along a given line of sight. Its detection is possible even when the metallicity is unknown, provided that the structure is not too embedded in the disk. Application of this method reveals the presence of a large group of M giant stars at a Galactocentric distance of 18$\pm 2$ kpc, over $+36\degr<b<+12\degr$ and $100\degr < l <270\degr$. Evidence that the stream extends to high negative latitudes is also found. That the structure contains M giants shows that it contains populations of at least an order of magnitude higher abundance than the [Fe/H] = -1.6 mean metallicity previously reported for this system. The structural characteristics of the stellar stream as traced by M giants do not support the interpretation of this structure as a homogeneously dense ring that surrounds the Galaxy, but as a more localized structure, possibly a merging dwarf galaxy with tidal arms, like the Sagittarius dwarf galaxy.