X-ray Analysis of Seyfert 2 Galaxies: Uncovering the Compton-Thick Population

Stephanie M. LaMassa, T. Heckman, A. Ptak, L. Martins, P. Sonnentrucker, C. Tremonti, A. Hornschemeier, V. Wild

Research output: Contribution to conferenceOtherpeer-review


Seyfert galaxies, local Active Galactic Nuclei (AGN), contain a nuclear accreting supermassive black hole surrounded by a torus of dust and gas. In Type 2 Seyfert galaxies (Sy2s) this systems is oriented such that the line of sight is through the obscuring torus, blocking the accretion disk and broad line region from view. When the column density of the torus exceeds 1.5 x 1024 cm-2, the source becomes "Compton-thick." Several proxies of intrinsic AGN luminosity do, however, exist: emission from gas formed in the narrow line region (which extends hundreds of parsecs above and below the torus), such as the [OIII] 5007 Angstrom and [OIV] 25.89 micron line, and infrared emission from the torus itself. A sample of Seyfert galaxies selected based on such isotropic diagnostics would therefore not be biased by the amount of obscuration present in the system. Subsequent X-ray observations can then be used to estimate the Compton-thick population as X-ray emission forms in a halo around the accretion disk and is thus subject to torus obscuration. We present the X-ray analysis of two homogeneous samples of Sy2s, selected based on isotropic indicators of AGN luminosity: one selected from the Sloan Digital Sky Survey based on a high observed [OIII] flux, and the other drawn from the original IRAS 12-micron sample. We estimate the fraction of Compton-thick sources in these two complementary samples by comparing the X-ray luminosity to various intrinsic AGN luminosity proxies and by spectral signatures of reprocessing, such as the equivalent width of the Fe K-alpha line. We estimate the amount of obscuration present in these systems and compare them to the column density derived from spectral fits. Finally, we search for correlations between host galaxy properties and Compton-thick diagnostics to investigate whether these obscured sources trace a unique host galaxy population.
Original languageEnglish
Publication statusPublished - 2010
EventAmerican Astronomical Society, 11th HEAD meeting - Waikoloa Village, Big Island, Hawaii, United States
Duration: 1 Mar 20104 Mar 2010


ConferenceAmerican Astronomical Society, 11th HEAD meeting
Country/TerritoryUnited States
CityWaikoloa Village, Big Island, Hawaii


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