Gaps in Globular Cluster Streams: Pal 5 and the Galactic Bar [GA]

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.

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S. Pearson, A. Price-Whelan and K. Johnston
Thu, 16 Mar 17

Comments: 5 Figures, 1 Table, submitted