Current Research

Hiding Active Galactic Nuclei

The basic energy source of an active galaxy is accretion onto a supermassive black hole. The central engine of such a galaxy---an active galactic nucleus (or AGN)---can be as luminous as the rest of the galaxy combined. However, there are several ways to hide these feeding monsters. Although AGN typically emit copious X-ray emission, they become orders of magnitude fainter when large amounts of material intervene along the line of sight. These so-called "Compton thick AGN" are easily missed in many current X-ray surveys, leading to misleading demographics in the census of black holes in the Universe.
The immediate surroundings of AGN are dusty, so the intrinsic radiation is reprocessed to emerge at infrared wavelengths. In studies at mid-infrared wavelengths, especially using the high spatial resolution of large telescopes on the ground, I aim to answer several key questions to determine the properties of these environments in detail. Specifically,
  • What is the nature of the surrounding material, and how is it distributed?
  • How do its properties depend on the AGN luminosity?
  • Do the dust characteristics change with AGN luminosity or activity?
  • What is the role of nuclear starbursts in feeding and obscuring AGN?

Starbursts in Active Galaxies

Even in active galaxies, stellar processes can also be significant, especially if a circumnuclear starburst is present. In this case, the collective effects of supernovae and massive-star winds can produce a superwind outflow, which may enrich the surrounding (intergalactic) medium. Concentrating on X-ray observations, I investigate the relationship between starbursts and AGN. Even at X-ray energies, starbursts alter the observed properties of AGN, and the two processes may be fundamentally related in an evolutionary sequence.
In current work, my collaborators and I find that AGN that contain starbursts exhibit extremely prominent fluorescent iron lines, and the distribution of material close to AGN and in the starbursts may be related.

Supernova Remnants and the ISM

I also study supernova remnants, which exploding stars produce. They are important as the source of mass and energy exchange in the interstellar medium, or ISM, regulating its structure. Individual, nearby remnants are a useful laboratory for the investigation of shock physics, and a probe of its environment.
Cygnus Loop My collaborators and I haved used data from the Chandra X-ray Observatory to understand the interaction between the Cygnus Loop supernova remnant's blast wave and a large interstellar cloud.

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