Astronomy Tea Talk

Stellar streams form through the tidal disruption of satellite galaxies or globular clusters orbiting a host galaxy. Globular cluster (GC) streams are of special interest because as thin streams they can exhibit density fluctuations and gap-like features that can be formed through interactions with dark matter subhalos. These gaps thus provide constraints for dark matter models: different prescriptions for the dark matter particle predict different subhalo mass functions. However, the currently known GC streams and stream gaps are limited to the Milky Way. With its large field of view (0.28 sq. deg.), deep imaging sensitivity, and high resolution, the Nancy Grace Roman Space Telescope presents a unique opportunity to significantly increase the number of observed globular cluster streams and gaps. In this talk, I will present a first exploration of the prospects for detecting gaps in streams in M31 and other nearby galaxies. Using a Pal 5-like stream, we model an encounter with a dark matter subhalo with a relative speed of 50 km/s, and we generate mock observations of this encounter together with background stars in M31 and foreground stellar Milky Way fields. We assess Roman's ability to detect gaps out to 10 Mpc both by visual inspection and by using a recently-developed gap-finding tool. We conclude that gaps from subhalos of masses > 5 x 10^6 solar masses are detectable within a 2-3 Mpc volume for exposure times between 1000s and 1 hour. The compilation of a large sample of these gaps in external galaxies will open up a new era of statistical analyses of gap characteristics in thin stellar streams and help constrain dark matter models.