Executive Summary

I am broadly interested in the physics of accretion onto compact objects. The main theme of my current work is accretion onto supermassive black holes in galactic nuclei and its connection to galaxy and black hole co-evolution. I am also actively working on executing the Black Hole Mapper project, which is a component of SDSS-V (the fifth installment of the Sloan Digital Sky Survey). This project will characterize the spectroscopic variability of quasars on very long time scales (comparable to or longer than the dynamical time scales of their broad-line regions). At the same time I am participating in a variety of other projects related to star formation in nearby galaxies and the astrophysics of gravitational wave sources. The latter category includes 

• searches for binary supermassive black holes via optical spectroscopy

• preparations for the identification of the electromagnetic counterparts of low-frequency gravitational wave sources 

• case studies of tidal disruption of stars by supermassive black holes and 

• surveys and case studies of high-mass X-ray binaries in nearby galaxies

I am primarily an observer, specifically a spectroscopist, but I occasionally work on theoretical models to help me with the interpretation of the data and with the design of observational campaigns. I often work at the interface between theory and observations: I use the data to test relatively sophisticated physical models and I participate in the refinement and further development of such models. I currently use telescopes at a variety of ground-based observatories for optical spectroscopy and the Hubble Space Telescope for UV spectroscopy. Moreover, I use optical and X-ray spectroscopic data from variety of archives and I participate in X-ray observing programs with the Chandra and XMM-Newton X-ray observatories.

Representative Projects That I Currently Lead or Co-Lead

Surveys for and Case Studies of Changing-Look Quasars (CLQs): Expanding the known population of CLQs through a variety of surveys and characterizing their demographics and variability properties. Studying the transitions of selected objects in details in order to constrain models for the physical mechanisms involved.

Preparing for LISA: Inventory of the content of typical error boxes of LISA sources and census of galaxies therein that can host massive black hole binaries. Assessment of the probability of confusion of the electromagnetic counterpart with an unrelated source within the error box (e.g., a steady, periodic or transient "imposter").

Dynamics of Accretion Flows in Active Galactic Nuclei: Studies of the broad emission-line profiles and their time variability. Comparison of the data with models that attribute the lines to accretion disks. Lead member of the All-Quasar Multi-Epoch Spectroscopy (AQMES) campaign now underway in SDSS-V.

Close, Binary Supermassive Black Holes: Search for their optical spectroscopic signature through long-term monitoring of radial velocity variations of the broad emission lines of selected quasars. Modeling of the line profiles in their optical spectra and the demographics of such systems. Study of the implications of population models for the low-frequency gravitational wave background.

Studies of the Central Engines of LINERs and Excitation Mechanisms of Their Nuclear Gas: Spatially resolved spectroscopy of the nuclei of several nearby galaxies with the Hubble Space Telescope to measure the spatial distribution of their emission lines and test models for the excitation of the gas in the nucleus.

Other Noteworthy Projects 

• Surveys and case studies of high-mass X-ray binaries in nearby, star-forming galaxies.

• Multi-wavelength surveys and case studies of ``changing-look'' quasars.

• Case studies of tidal disruption events.

• Study of narrow absorption lines in quasar spectra as probes of accretion disk winds.

• Accretion flows onto white dwarfs in cataclysmic variables.

• Population synthesis models of high-mass X-ray binaries.

• Observational study of star-formation in nearby galaxies using a combination of spatially resolved spectra from the MaNGA survey and UV images from Swift.