Program: GS-2014B-LP-2

Title:Probing the dark halo of the Milky Way with GeMS/GSAOI
PI:Tobias Fritz
Co-I(s): Tony Sohn, Nitya Kallivayalil, Mike Boylan-Kolchin, Rachael Beaton, Jo Bovy, Roeland van der Marel, Rodrigo Carrasco, Gulliermo Damke, Ric Davies, Steve Majewski


The Local Group, the regime in which detailed star-by-star studies can be done, is becoming a testbed for the study of the process of galaxy formation in general. This is because the constituents of the Local Group span a wide range of parameters such as star formation efficiency, dark matter halo size, and environment. These parameters can be turned into tests of the pressing questions governing both the cold dark matter theory and galaxy formation studies such as the distribution of matter on small scales and even the impact of reionization. A better estimate of the total Milky Way halo mass is important for many od these questions. Due to the mass anisotropy degeneracy it is not well determined from radial velocities. Current constraints on the shape of the halo are surprising: it is oblate, but misaligned by 90 degrees with the Disk. Proper motions are required in addition to the (generally known) radial velocities to test such halo models. Turning to the baryonic sector, while accretion evidently plays a role in galaxy formation, as attested by the existence of tidal debris streams, it is not yet excluded that some halo components formed in situ. To disentangle this process in detail, orbits are necessary. We propose to use GeMS/GSAOI to obtain proper motions, which are the missing phase space components, for a variety of tracers in the Milky Way halo, in order to constrain its shape and total mass, as well as the orbital histories of the tracers. This pioneering study will also produce an astrometric calibration suitable for other uses of GeMS/GSAOI. We request 143 h for our puposes.

Publications using this program's data