DESI DR1 Stream Tutorial

Background

Milky Way-like galaxies evolved hierarchically, accreting mass through many mergers within a dark matter (DM) halo. Stellar streams are a result of this process; a host galaxy's potential disrupts satellites (dwarf galaxies, globular clusters) leading them to form tidal tails.

Theories of cold and alternative DM disagree on predictions at the sub-galactic scale. Stellar streams offer a powerful means to indirectly constrain the DM substructure within the Milky Way.

However, to do this we need robust membership counts for stellar streams within our Galaxy. There are multiple ways to approach characterizing streams, but in this tutorial you will be walked through using finite mixture models to disentangle stellar streams from surrounding stars.

Mixture Modelling

Mixture models are powerful statistical tools to describe a set of datapoints that come from different distinct populations, even if we can't directly observe which data points belong to which group. In this tutorial, we will assume that the field of stars we narrow in on can be described by two distinct gaussian populations: one for the stream, and one for the 'background' (non-stream stars).