PI: Allyson A. Sheffield, Columbia University, firstname.lastname@example.org
Address: Astronomy Department, 550 W. 120th St., New York, NY 10027, USA
CoI: Kathryn V. Johnston, Columbia University
CoI: Steven R. Majewski, University of Virginia
Title: Testing Dynamical Models of Star Cloud Formation with the Hercules- Aquila Cloud
Abstract: This proposal requests time using the Goodman Spectrograph on the SOAR Telescope to map the radial velocity structure of the Hercules- Aquila cloud - a diffuse stellar substructure in the Galactic halo that spans hundreds of deg^2 on the sky. A handful of these amorphous substructures have been detected in the halo over the past decade and models suggest that, like stellar streams, these clouds are the remnants of debris from an accreted Milky Way satellite. However, the models have definite predictions that differentiate clouds from streams in: velocity (they should exhibit stronger radial velocity gradients than streams), origin (the progenitors should be on highly eccentric orbits) and location (the clouds should lie at the orbital apocenter of the parent satellite). Owing to their orbital dynamics, the debris from these clouds is expected to have explored a large range of radii, and hence should be sensitive to the radial profile of the Galactic dark matter distribution. Spectroscopic studies of M giants in the Triangulum-Andromeda cloud support the model predictions for the origin of stellar clouds (Rocha-Pinto et. al 2004 and the results from the work of NOAO proposal 2011B-0575). Our proposed spectroscopic program to target the Hercules-Aquila cloud will provide results that can: (1) further confirm the nature of these substructures as suggested by the models and (2) serve as new constraints on the Galactic potential.
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