Probing the fundamental halo properties of early-type galaxies using a new technique for wide-field stellar kinematics

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Dr. Romanowsky and his team will measure the motion of stars in the outer regions of elliptical galaxies. A European collaboration has already probed the central regions of such galaxies, finding an abundance of internal structures that are undoubtedly relics of the formation history. Dr Romanowsky will use a wide field multi-slit spectrograph on the 10-meter Keck telescope, which provides high efficiency over a wide field of view, to extend those measurements approximately 5 times further out in radius, to provide better constraints on the assembly history of the galaxy. These measurements will piggyback with observations of globular star clusters already planned with this telescope setup. The team will obtain both the chemical abundances in the stars and their motions from a near-infrared absorption feature of calcium. A pilot study of 5 galaxies has already shown that the motions and structure of the inner regions can be very different from those in the outer parts, where most of the galaxy's mass and angular momentum reside. A numerical technique that does not depend on any assumed symmetry properties of the galaxy will be used to find what combinations of the gravitational field and stellar orbits could give rise to the observed motions.An early-career scientist will be trained as a postdoctoral scholar. The team will develop their collaboration with Science Buddies, an online resource for K-12 science projects, to produce activities in extragalactic astronomy for the website. Among registered users of the site, 38% are girls; 8% identify themselves as African-American and 11% as Latino-American (38% chose 'other' or declined to respond).