As astrophysicists expand their knowledge of the formation and evolution of the Universe, tying large-scale cosmological galaxy formation scenarios to the measured and inferred details of individually observed galaxies has become increasingly feasible. This project is an integrated program of observational and theoretical studies designed to determine the distribution of both dark and luminous matter within a large sample of spiral galaxies and to compare these measurements with the predictions of galaxy formation in the concordance cosmological model.
Using the wide-field spectroscopic imaging Fabry-Perot instrument on the Southern African Large Telescope, the investigators propose to obtain high-resolution velocity maps of the galaxies, supplemented with more extended but lower resolution 21-cm maps from the Jansky Very Large Array (VLA) and, later, MeerKAT (Karoo Array Telescope). Combined with optical and near-infrared surface photometry, these data will be the basis for measurement of the total mass distribution within each galaxy. Stellar population synthesis estimates and detailed hydrodynamical modeling will determine the separation into baryonic and dark matter components. Extensive N-body simulations will test the stability of the models, sharpening the determination of the separate contributions of luminous and dark matter. After correction for the gravitational compression by the baryonic disk, the density, concentration, and circular speed of these halo models will be compared to the expected values derived from cosmological simulations. Discrepancies may suggest ways to improve and extend the physics in the galaxy formation simulations. A new analysis tool will measure non-axisymmetric patterns of motion in the two-dimensional kinematic maps of the galaxies, leading to a determination of the shapes of the dark halos. The investigators will also use Fabry-Perot observations of stellar absorption lines in early-type barred disk galaxies to determine the bar's rotation speed. As dynamical friction with the halo slows the bar's motion, this measurement will yield another constraint on the halo density in these galaxies. Sharpened by dynamical constraints, estimates for the mass-to-light ratios of galaxies aim to refine the poorly-known relation between mass-to-light and broad-band colors of disk galaxies.
Educationally, the proposing team will disseminate their results to the broader community through public lectures and in New Jersey schools. They will involve undergraduate and graduate students in their research and mentor them in their professional development in the sciences.
