Gaps in globular cluster streams: giant molecular clouds can cause them too

TL;DR

Thin stellar streams from globular clusters can reveal dark matter substructure through density gaps, but giant molecular clouds can also cause similar features, complicating the interpretation of such signals.

Contribution

This study demonstrates via N-body simulations that giant molecular clouds can create gaps in globular cluster streams, potentially mimicking dark matter subhalo effects.

Findings

GMCs can produce detectable gaps in GC streams.

Gaps caused by GMCs can resemble those from DM subhaloes.

Deep observations are needed to distinguish the causes of stream disturbances.

Abstract

As a result of their internal dynamical coherence, thin stellar streams formed by disrupting globular clusters (GCs) can act as detectors of dark matter (DM) substructure in the Galactic halo. Perturbations induced by close flybys amplify into detectable density gaps, providing a probe both of the abundance and of the masses of DM subhaloes. Here, we use N-body simulations to show that the Galactic population of giant molecular clouds (GMCs) can also produce gaps (and clumps) in GC streams, and so may confuse the detection of DM subhaloes. We explore the cases of streams analogous to the observed Palomar 5 and GD1 systems, quantifying the expected incidence of structure caused by GMC perturbations. Deep observations should detect such disturbances regardless of the substructure content of the Milky Way's halo. Detailed modelling will be needed to demonstrate that any detected gaps or clumps were produced by DM subhaloes rather than by molecular clouds.