Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External Galaxies with the Nancy Grace Roman Space Telescope

TL;DR

This paper explores the potential for the Nancy Grace Roman Space Telescope to detect gaps in stellar streams of external galaxies, which can provide insights into dark matter subhalo populations and properties.

Contribution

It presents a simulation-based assessment of Roman's capability to identify stream gaps in nearby galaxies, extending the study of dark matter effects beyond the Milky Way.

Findings

Gaps of about 1.5 kpc from subhalos ≥5×10^6 M☉ are detectable up to 10 Mpc.

Roman can observe approximately 150 galaxies within this volume, including 8 with high luminosity.

Large external galaxy samples will enable statistical analysis of stream gaps to constrain dark matter models.

Abstract

Stellar streams form through the tidal disruption of satellite galaxies or globular clusters orbiting a host galaxy. Globular cluster streams are exciting since they are thin (dynamically cold) and, therefore sensitive to perturbations from low-mass subhalos. Since the subhalo mass function differs depending on the dark matter composition, these gaps can provide unique constraints on dark matter models. However, current samples are limited to the Milky Way. With its large field of view, deep imaging sensitivity, and high angular resolution, the upcoming Nancy Grace Roman Space Telescope (Roman) presents a unique opportunity to increase the number of observed streams and gaps significantly. This paper presents a first exploration of the prospects for detecting gaps in streams in M31 and other nearby galaxies with resolved stars. We simulate the formation of gaps in a Palomar-5-like stream and generate mock observations of these gaps with background stars in M31 and the foreground Milky Way stellar fields. We assess Roman's ability to detect gaps out to 10 Mpc through visual inspection and with the gap-finding tool ${\texttt{FindTheGap}}$. We conclude that gaps of $\approx 1.5$ kpc in streams that are created from subhalos of masses $\geq5 \times 10^6$M$_{\odot}$ are detectable within a 2-3 Mpc volume in exposures of 1000s to 1 hour. This volume contains $\approx 150$ galaxies, including $\approx 8$ galaxies with luminosities $>10^{9}~$L$_{\odot}$. Large samples of stream gaps in external galaxies will open up a new era of statistical analyses of gap characteristics in stellar streams and help constrain dark matter models.