The Catholic University of America

Dr. Steven (Steve) B. Kraemer

Personal Information

Position: Ordinary Professor & Chair, Catholic University of America, Dept. of Physics
Mail Address: 200 Hannan Hall, Washington, DC 20064
Office Location: Catholic U. - 204 Hannan Hall
Fax: 202-319-4448

Research Interests

Dr. Kraemer is an extra-galactic astrophysicist and has extensive experience in the modeling of photoionized nebulae and the analysis of X-ray, UV, optical and IR spectra of active galaxies, in particular Seyfert galaxies. He has been PI of observing programs using Chandra, XMM-Newton, Hubble Space Telescope, and Spitzer. Dr. Kraemer was a co-investigator on the Space Telescope Imaging Spectrograph Instrument Development Team. Specific areas of research, which Kraemer conducts with Professor Mike Crenshaw (Georgia State University), Professor Jane Turner (UMBC), Dr. Henrique Schmitt (Naval Reseach Lab), Dr. Marcio Melendez (UMCP), Dr. T. Cody Fischer (GSU), among others, include:

  1. Mass Outflows in AGN and AGN feedback. The relationship between the mass of the central bulge of galaxies and that of the super-massive black holes that reside within suggests co-evolution. One possible mechanism is the clearing of gas by winds generated by the AGN, i.e. "AGN feedback". Mass outflows, in the form of blueshifted absorption lines in the UV and X-ray, are found in approximately half of all Seyfert galaxies, with radial velocities up to several 1000 km/s. These outflows may be powerful enough to affect the host galaxy and hence may provide insight into AGN feedback processes.
  2. Physical conditions in the gas in the narrow-line regions (NLR) of Seyfert galaxies. Of particular interest is the question: is this gas ionized solely by EUV-Xray radiation from the central nuclear source or are there other important effects, such as ionization by relativistic particles associated with radio ``jets''? Furthermore, we have found that star-formation makes a significant contribution to the mid-IR emission-line spectra of many Seyfert galaxies and, likely, to optical spectra of the NLR.
  3. The kinematics of the narrow-line gas in Seyfert galaxies. Understanding the motion of gas in the inner regions of Seyfert galaxies may provide important clues regarding the evolution of this phase of activity. By combining the kinematic studies with the physical parameters of the NLR derived from photo-ionization modeling, we have found that NLR outflows may be more important to AGN feedback than outflows originating close to the AGN.


Other Stuff

Steve Kraemer is the only member of the American Astronomical Society to get a mention in Christiane Bird's "Guide to Live Jazz and Blues in the U.S."

Additional Information

Selected Recent Papers

"Feedback from Mass Outflows in Nearby Active Galactic Nuclei. I. Ultraviolet and X-Ray Absorbers", Crenshaw, D. M., Kraemer, S. B. 2012, ApJ, 753, 75

"Observations of Outflowing Ultraviolet Absorbers in NGC 4051 with the Cosmic Origins Spectrograph", Kraemer, S. B., Crenshaw, D. M., Dunn, J. P., Turner, T. J., Lobban, A. P., Miller, L., Reeves, J. N.,
Fischer, T. C., Braito, V. 2012, ApJ, 751, 84
" Uncovering the Spectral Energy Distribution in Active Galaxies Using High-ionization Mid-infrared Emission Lines"   Meléndez, M., Kraemer, S. B., Weaver, K. A., Mushotzky, R. F. 2011, ApJ, 738, 6

"X-Ray Characteristics of NGC 3516: A View through the Complex Absorber", Turner, T. J., Miller, L., Kraemer, S. B., Reeves, J. N. 2011, ApJ, 733, 48

"Multi-wavelength Probes of Obscuration Toward the Narrow-line Region in Seyfert Galaxies", Kraemer, S. B., Schmitt, H. R., Crenshaw, D. M., Meléndez, M., Turner, T. J., Guainazzi, M., Mushotzky, R. F. 2011,
ApJ, 727, 130

"Hubble Space Telescope Observations of the Double-peaked Emission Lines in the Seyfert Galaxy Markarian 78: Mass Outflows from a Single Active Galactic Nucleus" Fischer, T. C., Crenshaw, D. M., Kraemer, S. B.,
Schmitt, H. R., Mushotsky, R. F., Dunn, J. P. 2011, ApJ, 727, 71