Current Research Questions
What physical processes control the spectra and variability of active galaxies, both at high energies and across the electromagnetic spectrum?
How have winds and jets from active galactic nuclei shaped typical massive galaxies?
What is the demography of the accreting supermassive black hole population over cosmic time, especially in the most highly obscured systems?
How did the first supermassive black holes in the Universe feed and grow?
How have the X-ray properties of starburst and normal galaxies evolved over cosmic time, and what does this imply about the evolution of their accreting X-ray binary populations?
Some Research Milestones and Discoveries
Creation of the most sensitive X-ray surveys of the extragalactic universe. These have significantly constrained the cosmic growth of supermassive black holes, determined the importance of black-hole
accretion within the overall cosmic energy budget, measured the active galactic nucleus content of forming massive galaxies, and detected X-ray emission from cosmologically distant starburst and normal galaxies.
Studies of winds from active galaxies, ranging from local Seyfert galaxies to distant quasars. X-ray gratings studies of Seyfert winds have utilized hundreds of detected atomic features to provide qualitatively new information about wind physical conditions, kinematics, and geometry, and X-ray spectroscopy of distant quasars has clarified their wind geometries, mass-ejection rates, and role in feedback.
X-ray observations of the first supermassive black holes in the Universe. My group has increased the number of X-ray detected active galaxies at z > 4 by more than an order of magnitude, showing that X-ray emission is a universal and stable property of accreting supermassive black holes out to the reionization epoch.
Currently Utilized and Upcoming Research Facilities
Chandra X-ray Observatory
Swift Gamma-Ray Burst Explorer
Nuclear Spectroscopic Telescope Array (NuSTAR)
Hubble Space Telescope
Spitzer Space Telescope
Sloan Digital Sky Survey-III
Large Synoptic Survey Telescope