Star Forming Galaxies
The conversion of gas into stars is a fundamental characteristic of galaxies. Building an understanding of star formation processes involves several astrophysical areas. Radio measurements supply information on star formation reservoirs in the form of atomic and molecular gas, respectively revealed by 21-cm and cm-to-submillimeter radio observations. To this end Wisconsin astronomers make use of a range of radio facilities from single-dish telescopes to interferometers, including the Very Large Array and in the near future, the Atacama Large Millimeter array (ALMA).
On the other side of the equation several of our projects are exploring the nature of galactic stellar populations. These assessments include fundamental measurements of stellar masses through the analysis of disk structures to model fitting of spectral energy distributions to determine the mixes of stellar ages. This work is largely based on UV-optical-near infrared photometric and spectroscopic data taken with a variety of ground-based telescopes, but especially WIYN and SALT, as well as with other unique facilities, such as the Hubble Space Telescope.
The question of star formation feedback and regulation also are of particular interest at UW-Madison. Observations show that once galaxies settle down from an initial phase of exuberant star formation, most systems maintain roughly constant stellar production rates until they become dead red stellar fossils. This behavior implies that processes exist which stabilize star formation rates. For example, the energy from supernova blasts may dynamically heat the ISM, thereby reducing star formation over the longer term, while also locally stimulating star formation around a young stellar system. Research on this topic by UW-Madison astronomers includes measurements of the physical state and kinematics of stars in gas. Investigations of starburst galaxies, cases where galaxies have star formation rates that are too high to sustain over cosmic time scales, are especially useful in revealing how feedback works, as well as offering insights into other processes, such as the generation of galactic winds.