Probing the Dark Matter Halos of External Galaxies with Stellar Streams

Abstract Stellar streams have proven to be powerful tools for measuring the Milky Way’s gravitational potential and hence its dark matter (DM) halo. In the coming years, the Vera Rubin Observatory, Euclid, ARRAKIHS, and the Nancy Grace Roman Space Telescope will uncover a plethora of streams around external galaxies. Although great in number, observations of these distant streams will often be limited to only the on-sky position of the stream. In this work, we explore how well we will be able to measure the DM halos of these galaxies by fitting simplified mock streams with a variety of intrinsic and orbital properties in a range of data availability scenarios. We find that results vary based on the interplay between the amount of information provided by a stream’s intrinsic properties versus that of the observational uncertainties, as well as on the form of potential assumed. In general, we find streams with multiple wraps around their host galaxy can constrain the overall radial profile and scale radius of the potential without radial velocities. In many other cases, a single radial velocity measurement often provides a significant boost to constraining power for the radial profile, scale radius, and enclosed mass of the DM halo. Given the wealth of data expected soon, this suggests that we will be able to measure the DM halos of a statistically significant sample of galaxies with stellar streams in the coming years.