Exploring the reality of density substructures in the Palomar 5 stellar stream

TL;DR

This study investigates the substructures in the Palomar 5 stellar stream, revealing that most observed features are likely due to observational artifacts rather than real physical structures, through analysis of survey data and simulations.

Contribution

The paper demonstrates that apparent substructures in the Palomar 5 stream are mainly artifacts of observational inhomogeneities, challenging previous interpretations of these features.

Findings

Most substructures are artifacts of observational inhomogeneities.

Real physical density variations are linked to stellar epicyclic motions but are less significant when considering observational constraints.

Artificial models show similar substructures to real data, indicating observational effects dominate.

Abstract

We present an analysis of the presence of substructures in the stellar stream of the Palomar 5 globular cluster, as derived from Sloan Digital Sky Survey data. Using a matched filter technique, we recover the positions and sizes of overdensities reported in previous studies. To explore the reality of these structures, we also create an artificial model of the stream, in which we construct a realistic background on top of which we add a perfectly smooth stream structure, taking into account the effects of photometric completeness and interstellar extinction. We find that the smooth artificial stream then shows similarly-pronounced substructures as the real structure. Interestingly, our best-fit N-body simulation does display real projected density variations linked to stellar epicyclic motions, but these become less significant when taking into account the SDSS star-count constraints. The substructures found when applying our matched filter technique to the N-body particles converted into observable stars are thus mostly unrelated to these epicyclic motions. This analysis suggests that the majority of the previously-detected substructures along the tidal tail of Palomar 5 are artefacts of observational inhomogeneities.