Research Interests

My research is focused on observational extragalactic astronomy and cosmology. One of my main interests is to use observations of the stellar contents and chemical compositions of galaxies to trace their evolution, and to understand the underlying physical processes that drive this evolution. This research has produced some of the most widely used methods for measuring the rates of star formation in galaxies, and quantified the changes in star formation rates and histories along the Hubble sequence of galaxy types. These changes in star formation activity now appear to be driven almost entirely by underlying variations in the density of interstellar gas, following a well-defined scaling law, coupled with a star formation threshold at low density. The gas distributions in turn are regulated by a combination of internal (secular) evolutionary processes along with externally triggered events such as tidal interactions and galactic mergers, which influence the flow of gas both within galaxies and between the galaxies and their surroundings. My other main research area is in observational cosmology, including the calibration of the extragalactic distance scale and Hubble constant using the Hubble Space Telescope. Our team's result has contributed to the current "concordance" cosmology of an accelerating Universe dominated by dark energy and dark matter.

Membership Type


Election Year


Primary Section

Section 12: Astronomy

Secondary Section

Section 13: Physics