B.S. New Mexico Institute of Mining and Technology (1983)
Ph.D. Montana State University (1991)
I have been studying spectra from the central engine of active galaxies and quasars for more than 30 years. While I do some modeling, my approach is principally observational; I have experience using infrared, optical, ultraviolet and X-ray data. My current area of interest is Broad Absorption Line Quasars (BALQs). These objects show evidence for outflows with velocities sometimes exceeding one tenth of the speed of light. The energy carried by these outflows can, in principle, influence the evolution of their host galaxies in a process called feedback. BAL outflows have been known since the 1980s to occur in about 10% of optically selected quasars, but quantitative analysis has been stymied by the line blending and partial covering common in the spectra. Our group has developed a novel spectral-synthesis code, SimBAL, which derives physical conditions in the absorbers using large grids of ionic column densities generated by the photoionization code Cloudy and a Bayesian model calibration. SimBAL offers many advantages over traditional spectral analysis methods, including the ability to fit complex spectra with significantly blended absorption lines. Using SimBAL, we have analyzed the spectra of more than 100 iron low-ionization BALQs (Choi et al. 2022, Choi et al. in prep.), increasing the number in the literature with detailed analysis by more than a factor of 10. Key findings to date are that the outflows lie at a wide range of distances from the central engine, and the outflow properties are linked to the quasar accretion rate, supporting an evolutionary role for these objects.
