3 years ago

The Hercules stream as seen by APOGEE-2 South.

Jose G. Fernandez-Trincado, Dmitry Bizyaev, Christopher Wegg, Pedro A. Palicio, Felipe A. Santana, Alexandre Roman-Lopes, Jon A. Holtzman, Jo Bovy, Drew Chojnowski, Steven R. Majewski, Angeles Pérez-Villegas, Kaike Pan, Richard R. Lane, Ortwin Gerhard, Jennifer Sobeck, Jason A. S. Hunt, Penélope Longa-Peña, Andrés Almeida

The Hercules stream is a group of co-moving stars in the Solar neighbourhood, which can potentially be explained as a signature of either the outer Lindblad resonance (OLR) of a fast Galactic bar or the corotation resonance of a slower bar. In either case, the feature should be present over a large area of the disc. With the recent commissioning of the APOGEE-2 Southern spectrograph we can search for the Hercules stream at $(l,b)=(270^\circ,0)$, a direction in which the Hercules stream, if caused by the bar's OLR, would be strong enough to be detected using only the line-of-sight velocities. We clearly detect a narrow, Hercules-like feature in the data that can be traced from the solar neighbourhood to a distance of about 4 kpc. The detected feature matches well the line-of-sight velocity distribution from the fast-bar (OLR) model. Confronting the data with a model where the Hercules stream is caused by the corotation resonance of a slower bar leads to a poorer match, as the corotation model does not predict clearly separated modes, possibly because the slow-bar model is too hot.

Publisher URL: http://arxiv.org/abs/1709.02807

DOI: arXiv:1709.02807v2

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