Gaps and length asymmetry in the stellar stream Palomar 5 as effects of Galactic bar rotation

TL;DR

This paper shows that the rotation of the Galactic bar can explain observed asymmetries and gaps in the Palomar 5 stellar stream, impacting the interpretation of dark matter subhalo interactions.

Contribution

It introduces the effect of the Galactic bar's pattern speed on Palomar 5's stream, explaining observed features not accounted for in previous models.

Findings

Galactic bar rotation causes gaps in Palomar 5 stream.

Bar-induced torques lead to energy offsets in stream stars.

Implications for using streams to detect dark matter subhalos.

Abstract

Recent Pan-STARRS data show that the leading arm from the globular cluster Palomar 5 (Pal 5) appears shorter than the trailing arm, while simulations of Pal 5 predict similar angular extents. We demonstrate that including the spinning Galactic bar with appropriate pattern speeds in the dynamical modeling of Pal 5 can reproduce the Pan-STARRS data. As the bar sweeps by, some stream stars experience a difference in net torques near pericenter. This leads to the formation of apparent gaps along Pal 5's tidal streams and these gaps grow due to an energy offset from the rest of the stream members. We conclude that only streams orbiting far from the Galactic center or streams on retrograde orbits (with respect to the bar) can be used to unambiguously constrain dark matter subhalo interactions. Additionally, we expect that the Pal 5 leading arm debris should re-appear south of the Pan-STARRS density truncation.