Variations in the width, density, and direction of the Palomar 5 tidal tails

TL;DR

This study uses deep photometry to analyze the Palomar 5 tidal tails, revealing their complex structure, density variations, and directional changes, which can inform understanding of galactic perturbations including dark matter subhalos.

Contribution

It provides the clearest view of Palomar 5's tidal tails beyond 20 kpc and highlights the need for additional perturbation sources beyond a simple Milky Way bar model.

Findings

Detected a wide, low surface-brightness extension of the leading tail

Observed significant density variations along the stream

Identified sharp directional changes in the tails

Abstract

Stars that escape globular clusters form tidal tails that are predominantly shaped by the global distribution of mass in the Galaxy, but also preserve a historical record of small-scale perturbations. Using deep $grz$ photometry from DECaLS, we present highly probable members of the tidal tails associated with the disrupting globular cluster Palomar 5. These data yield the cleanest view of a stellar stream beyond $\sim20\,\rm kpc$ and reveal: (1) a wide, low surface-brightness extension of the leading tail; (2) significant density variations along the stream; and (3) sharp changes in the direction of both the leading and the trailing tail. In the fiducial Milky Way model, a rotating bar perturbs the Palomar 5 tails and can produce streams with similar width and density profiles to those observed. However, the deviations of the stream track in this simple model do not match those observed in the Palomar 5 trailing tail, indicating the need for an additional source of perturbation. These discoveries open up the possibility of measuring the population of perturbers in the Milky Way, including dark-matter subhalos, with an ensemble of stellar streams and deep photometry alone.