TASTY: Characterizing Stellar Streams using 6-D Kinematics and Chemistry

Speaker: Nasser Mohammed

Abstract: Milky Way-like galaxies evolved hierarchically within a dark matter halo, accreting mass through many mergers. Stellar streams are a result of this process, where the host galaxy’s potential disrupts satellite dwarf galaxies or globular clusters (GC), leading them to form tidal tails. Current techniques for stream characterization are applied to Gaia DR3, relying heavily on proper motion measurements to study the stream. Using the Dark Energy Spectroscopic Instrument Milky Way Survey (DESI MWS), we obtain radial velocity measurements for orders of magnitude more stars to much fainter magnitudes than current efforts. We use a Bayesian mixture model to characterize the stream population in proper motions, radial velocity, and metallicity, imbedded in a background population of Milky Way halo stars. We apply our methods first to the C-19 stellar stream, identifying 2x the number of spectroscopically confirmed member stars for the stellar stream. C-19 merits particular interest for two primary reasons. First, while C-19 hosts chemical abundance characteristics of a GC; the observed kinematics of the stream are difficult to reconcile with a purely baryonic, disrupting-GC scenario. We measure a velocity dispersion of 8.9+1.8−1.4 kms−1 and a mean metallicity of [Fe/H] = −3.25+0.12−0.10, with an upper bound on its metallicity dispersion σ[Fe/H] of 0.35±0.1; we conclude that our measurements are in line with previous works identifying C-19 as a ‘hot’, metal-poor stream. In the future we plan to apply our stream characterization pipeline to all the progenitor-free stellar streams in the DESI MWS footprint.