Gaps In Globular Cluster Streams: Pal 5 And The Galactic Bar (speaker: Sarah Pearson, Columbia)

Monday April 3, 2017 12:05 pm
Marlar Lounge 37-252

Stellar tidal streams in the Milky Way form as globular clusters and dwarf galaxies tidally disrupt in the Milky Way’s Galactic potential. Their dynamical evolution can be used to constrain Galactic parameters such as the distribution of dark matter. Additionally, it has been hypothesized that thin stellar streams can serve indirect detection sights for dark matter subhalos as gaps form when they interact with the streams. In principle, this enables an investigation of the predicted power spectrum of dark matter subhalos in our Galaxy and therefore a direct test of LCDM. In this talk I focus on the globular cluster stream Palomar 5 (Pal 5), which has received much attention since its discovery due to its constraining power on the Galactic potential and due to apparent gaps along its stream. Recent Pan-STARRS data show that the leading arm from Pal 5 appears shorter than the trailing arm, while simulations of Pal 5 predict similar angular extents. I 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. I 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,  the Pal 5 leading arm debris should re-appear south of the Pan-STARRS density truncation, which, if detected, can provide a constraint on the bar pattern speed.