Dark Matter Halos of the Most Massive Galaxies

Murphy Jeremy D, Austin TX

Investigators

Abstract

Dr. Jeremy D. Murphy is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at Princeton University. The current cosmological paradigm includes a significant and unknown physical entity called "dark matter." While the presence of dark matter (DM) in galaxies is well established, the extent of galaxy DM halos and the role DM plays in galaxy formation and evolution is largely unknown. As the current cosmological paradigm governing the hierarchical clustering of DM halos makes specific predictions about their formation timescales and merger history, a clear understanding of the mass of DM halos on galaxy scales is needed. In this project the fellow will focus on directly constraining the mechanisms and timescales of elliptical galaxy formation. The recent discovery of quiescent, red elliptical galaxies at redshift around z~2 raises many questions regarding the Lambda Cold Dark Matter hierarchical picture of galaxy formation. Fortunately, galaxies leave both chemical and kinematic clues to their formation histories. Advances in integral field spectroscopy and dynamical modeling have begun to open the window into understanding the DM distribution, DM central density, the stellar orbital anisotropy and chemical abundance gradients of elliptical galaxies. In this project the fellow will continue his study of the formation and evolution of massive elliptical galaxies. Specifically, this project has the following aims: (1) The fellow will use 2D stellar kinematics from VIRUS-P and orbit-based, axisymmetric dynamical modeling to constrain the DM halo mass, the DM central density, the stellar orbital anisotropy and stellar abundance gradients. From this he will be able to place direct constraints on the timescales and possible mechanisms of galaxy formation. (2) The fellow will compare mass estimates based on stellar kinematics to other methods of estimating mass in galaxies in order to quantify any systematics between these different methods. (3) The fellow will bring his experience with the commissioning of the VIRUS-P spectrograph, and his detailed study of the instrument's fiber optics, in order to successfully install a duplicate instrument on the DuPont telescope at Las Campanas Observatory. He will then use this instrument to expand his current galaxy sample into the Southern Hemisphere. The broader impacts of this project include a significant educational component. The fellow will develop and teach a new course for the Prison Teaching Initiative (PTI). The PTI program teaches college-credit courses to inmates at two youth correctional facilities near Princeton University. The students can earn a two-year degree through the program and go onto four-year colleges upon release. The course will focus on physics and astronomy and aim to develop both a scientific approach to problem solving and an appreciation of the practical application of science in daily life. The large majority of evidence indicates that improving education in a prison population is the leading cause in reducing a return to crime upon release. The fellow will bring his previous teaching skills and enthusiasm for science to a deserving, underrepresented population.