BAT AGN Spectroscopic Survey. VIII. Type 1 AGN with Massive Absorbing Columns

T. Taro Shimizu, Richard I. Davies, Michael Koss, Claudio Ricci, Isabella Lamperti, Kyuseok Oh, Kevin Schawinski, Benny Trakhtenbrot, Leonard Burtscher, Reinhard Genzel, Ming Yi Lin, Dieter Lutz, David Rosario, Eckhard Sturm, Linda Tacconi

Research output: Contribution to journalArticlepeer-review


We explore the relationship between X-ray absorption and optical obscuration within the BAT AGN Spectroscopic Survey (BASS), which has been collecting and analyzing the optical and X-ray spectra for 641 hard X-ray selected (E > 14 keV) active galactic nuclei (AGNs). We use the deviation from a linear broad Hπ-to-X-ray relationship as an estimate of the maximum optical obscuration toward the broad line region (BLR) and compare the A V to the hydrogen column densities () found through systematic modeling of their X-ray spectra. We find that the inferred columns implied by A V toward the BLR are often orders of magnitude less than the columns measured toward the X-ray emitting region, indicating a small-scale origin for the X-ray absorbing gas. After removing 30% of Sy 1.9s that potentially have been misclassified due to outflows, we find that 86% (164/190) of the Type 1 population (Sy 1-1.9) are X-ray unabsorbed as expected based on a single obscuring structure. However, 14% (26/190), of which 70% (18/26) are classified as Sy 1.9, are X-ray absorbed, suggesting that the BLR itself is providing extra obscuration toward the X-ray corona. The fraction of X-ray absorbed Type 1 AGNs remains relatively constant with AGN luminosity and Eddington ratio, indicating a stable BLR covering fraction.

Original languageEnglish
Article number154
JournalAstrophysical Journal
Issue number2
StatePublished - 1 Apr 2018
Externally publishedYes


  • galaxies: Seyfert
  • galaxies: active
  • galaxies: nuclei


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