Circumnuclear Star Formation and Heavy Obscuration Revealed by Chandra in NGC 4968
Abstract
NGC 4968 is a nearby Seyfert 2 galaxy with evidence of extreme obscuration and circumnuclear star formation in its Chandra spectrum. Imaging analysis in the soft band (0.5 - 2 keV) reveals extended (~1 kpc) emission that is thermal in nature and ascribed to on-going star formation. We measure an Fe Kα equivalent width (EW) value of ~2.5 keV which is a clear indicator of Compton-thick levels of obscuration. Using physically motivated X-ray spectral models that self consistently treat the transmitted continuum, Compton scattered emission, and fluorescent line emission, we measure a column density above 1.25 x 1024 cm-2, though are unable to determine, with present data, whether the X-ray reprocessor takes the form of a toroidal or spherical geometry (in which case the column density may exceed 1025 cm-2). A spherical distribution of matter facilitiates the production of extreme Fe Kα EWs, suggesting that this geometry may be preferred. We speculate that on-going star formation increases the covering factor of the circumnuclear obscuration enshrouding the AGN. With upcoming NuSTAR observations, we will test whether the X-ray reprocessor geometry is indeed spherical and derive better constraints on the obscuring column density.
- Publication:
-
AAS/High Energy Astrophysics Division #16
- Pub Date:
- August 2017
- Bibcode:
- 2017HEAD...1610610L