A Detection of Gas Associated with the M 31 Stellar Stream

TL;DR

This study detects and characterizes gas associated with the M 31 stellar stream using high-resolution ultraviolet spectra, revealing distinct kinematic components and metallicity consistent with galaxy halo environments.

Contribution

It provides the first high-resolution UV absorption spectra evidence of gas in the M 31 stellar stream, linking gas properties to stellar populations and halo characteristics.

Findings

Detection of gas in the M 31 stellar stream

Identification of multiple velocity components in the gas

Gas metallicity consistent with galaxy halo environments

Abstract

Detailed studies of stellar populations in the halos of the Milky Way and the Andromeda (M 31) galaxies have shown increasing numbers of tidal streams and dwarf galaxies, attesting to a complicated and on-going process of hierarchical structure formation. The most prominent feature in the halo of M 31 is the Giant Stellar Stream, a structure ~4.5 degrees in extent along the sky, which is close to, but not coincident with the galaxy's minor axis. The stars that make up this stream are kinematically and chemically distinct from the other stars in the halo. Here, we present HST/COS high-resolution ultraviolet absorption spectra of three Active Galactic Nuclei sight lines which probe the M 31 halo, including one that samples gas in the main southwestern portion of the Giant Stream. We see two clear absorption components in many metal species at velocities typical of the M 31 halo and a third, blue-shifted component which arises in the stream. Photoionization modeling of the column density ratios in the different components shows gas in an ionization state typical of that seen in other galaxy halo environments and suggests solar to slightly super-solar metallicity, consistent with previous findings from stellar spectroscopy.