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N. A. Levenson (Univ. Kentucky), K. A. Weaver (NASA/GSFC and JHU), T. M. Heckman (JHU)
Circumnuclear starbursts are common in Seyfert 2 galaxies, producing distinct X-ray signatures. As we demonstrate with new Chandra observations of such starburst/AGN composite galaxies, stellar processes also generate significant soft X-ray emission. We specifically analyze X-ray spectra and images of NGC 5135 and NGC 7130, two heavily-obscured (NH > 1024 {\mathrm \,cm-2}) starburst/AGN composite galaxies. In each case, the majority of the soft X-ray emission is spatially extended and has a thermal spectrum, while the AGN accounts for most of the hard (E > 2 keV) emission. The hard continuum is spectrally flat (photon index \Gamma \approx 0), indicating that it is strongly reprocessed, not viewed directly. Similar to other heavily-obscured active galactic nuclei, in both cases the equivalent width (EW) of the iron K\alpha fluorescence line is very large; (EW \approx 2 and 1 keV in NGC 5135 and NGC 7130, respectively). The geometry of an obscuring torus of material near the AGN determines the Fe emission. In general, starburst/AGN composite galaxies require small opening angles and present few direct lines of sight to their central engines. These composite galaxies are common, and their large covering fractions and heavy obscuration effectively hide their intrinsically bright X-ray continua.
The author(s) of this abstract have provided an email address for comments about the abstract: levenson@pa.uky.edu
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.