NOAO >   Observing Info >   Approved Programs >   2009B-0104

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Proposal Information for 2009B-0104


PI: Alan McConnachie, NRC Herzberg Institute of Astrophysics, alan.mcconnachie@nrc.ca
Address: Dominion Astrophysical Observatory, 5071 West Saanich Road, Victoria, British Columbia V9E 2E7, Canada

CoI: Scott Chapman, University of Cambridge
CoI: Rodrigo Ibata, Observatoire de Strasbourg
CoI: R. Michael Rich, UCLA
CoI: Mike Irwin, University of Cambridge
CoI: Mark Fardal, University of Massachusetts
CoI: John Dubinski, University of Toronto
CoI: Jorge Penarrubia, University of Cambridge
CoI: Larry Widrow, Queens University
CoI: Annette Ferguson, University of Edinburgh

Title: A direct measure of the dark mass of M31

Abstract: We propose to obtain radial velocities for red giant branch stars in a newly discovered, vast, stellar stream, coherent over ~ 70 kpc at typical radii of 40 kpc from the center of the M31 galaxy. Coupled with our exquisite extant photometry covering M31 and its surrounding structures, the requested kinematics (sampled at 4 positions along the stream) will enable us to determine the orbit of the stream and identify its progenitor; there is a tantalizing possibility that it is linked to Andromeda I, but kinematics are required to test this hypothesis. By using this stream as a potentiometer, we will therefore determine the total mass of M31 contained within the orbit. This will represent an independent and direct measure of the gravitational potential - the dark matter content - of an L_\star galaxy; it can only be achieved using the multiplexing capabilities and high throughput of the Keck/DEIMOS instrument.


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