Signatures of LCDM substructure in tidal debris

TL;DR

This paper investigates how dark matter substructure affects tidal streams in the Milky Way, finding that orbital parameters and halo shape are more influential than substructure, which slightly increases stream clumpiness and can alter debris locations.

Contribution

The study provides a detailed simulation analysis showing that dark matter substructure has subtle effects on tidal streams, challenging previous assumptions about their detectability.

Findings

Halo shape and orbit influence stream disruption more than substructure.

Substructure increases clumpiness and can make streams appear more compact.

Differences in debris location due to substructure may impact observational interpretations.

Abstract

In the past decade, surveys of the stellar component of the Galaxy have revealed a number of streams from tidally disrupted dwarf galaxies and globular clusters. Simulations of hierarchical structure formation in LCDM cosmologies predict that the dark matter halo of a galaxy like the Milky Way contains hundreds of subhalos with masses of ~10^8 solar masses and greater, and it has been suggested that the existence of coherent tidal streams is incompatible with the expected abundance of substructure. We investigate the effects of dark matter substructure on tidal streams by simulating the disruption of a self-gravitating satellite on a wide range of orbits in different host models both with and without substructure. We find that the halo shape and the specific orbital path more strongly determine the overall degree of disruption of the satellite than does the presence or absence of substructure, i.e., the changes in the large-scale properties of the tidal debris due to substructure are small compared to variations in the debris from different orbits in a smooth potential. Substructure typically leads to an increase in the degree of clumpiness of the tidal debris in sky projection, and in some cases a more compact distribution in line-of-sight velocity. Substructure also leads to differences in the location of sections of debris compared to the results of the smooth halo model, which may have important implications for the interpretation of observed tidal streams. A unique signature of the presence of substructure in the halo which may be detectable by upcoming surveys is identified. We conclude, however, that predicted levels of substructure are consistent with a detection of a coherent tidal stream from a dwarf galaxy.