Galaxy kinematics - the measurement of the motions of luminous gas and stars -- provides fundamental tools for answering basic questions about when and how disk galaxies formed. For example, these motions allow us to infer the distribution of dynamical mass within galaxies, and hence the shape of their gravitational potentials. Kinematics also enable us to probe the dynamical state of the luminous baryons trapped within theses potentials by providing measures of angular momentum and dynamical temperature (the ratio of kinetic energy in random motion vs. ordered rotation). The combination of of kinematic measurements of gas (sticky) and stars (collisionless) allows us to separate the energetics due to mass accretion and dynamical instabilities from stellar and AGN feed-back. This in turn allows us to disentangle if and when gas is lost from the disk to the intergalactic medium, or recycled back into the disk.
Our department has a strong observational and theoretical focus on galaxy kinematics and their dynamical interpretation, as well as on stellar and AGN feedback, underpinned by the development of unique instrumentation for our telescope facilities. We have expertise in the study of galaxy kinematics over a wide range of galaxy types from large, normal spiral galaxies to irregular, late-type systems, to star-bursts at low and high redshift. Our observational strengths include optical integral-field spectroscopy (IFS) of ionized gas and stars, and neutral-hydrogen studies using single-dish and
aperture-synthesis arrays. We have lead the development of IFS systems on the WIYN 3.5m telescope and the Wisconsin H-alpha Mapper (WHAM); we are developing new IFS systems for our 11m telescope, SALT; and we are members of the US SKA consortium.
Questions for which we actively pursue answers include:
How are galaxy disks assembled and heated? An unambiguous prediction of cold-dark-matter structure-formation scenarios is that disks form late, at relatively recent times. The dynamically cold nature of disks limits the accretion rate at any given time, but provides little further constraint on the history of matter accretion onto disks, or their heating via dynamical or feedback processes. Observationally, the matter accretion rate has not been determined at any epoch. Several programs here are filling this gap in our knowledge by studying a variety of galaxy types at different look-back times and
How much mass is actually in galaxy disks -- is their rotation maximally supported at small radii by the mass of the disk? The answer to this question has profound implications for the shape of dark-matter halos, and hence on galaxy formation scenarios. Equally important, the answer to this questions provides the mass-to-light ratio of disk stellar populations, and thereby places limits on the faint-end of the initial mass function in galaxies outside of the
Milky Way, and other forms of dark-matter in the disk (e.g., stellar remnants, molecular gas, or sticky dark-matter). Some of the unique instruments developed here are being used to measure the mass in galaxy disks today.
A common theme throughout our collaborative research is spectroscopy -- a tool which allows us to tie our kinematic measurements into studies of abundances and stellar populations essential for a complete picture of the life-cycle of baryons in the universe.