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Astrophysics Talk

The near-infrared view of the BLR and the effect of obscuration in BLR characterisation of local hard X-ray selected AGN

Federica Ricci (DIFA, Univ. Bologna)

Tuesday 20/10/2020 @ 14:00, Google Hangouts Meet

Understanding geometry of the material in the broad line region (BLR) can shed light on the physics in the proximity of active galactic nuclei (AGN). Three BLR properties, the cloud velocity distribution, their distance from the central supermassive black hole (BH) and the virial factor f, are directly involved in BH mass (Mbh) determination. Systematics about the BLR dynamics are encoded in the virial factor f, that is a scale factor upon which all the virial Mbh estimates are rooted, and affects up to ?2-3 the Mbh uncertainties. The f-factor has been directly determined on a small sample of local broad-line AGN, allowing the community to infer a correlation between f and line-of-sight inclination. However, little is known about the BLR and f-factor in obscured AGN. Understanding whether biases arise in MBH estimation with increasing obscuration is possible only by studying an obscuration unbiased (hard) X-ray selected AGN statistical sample in the rest-frame near-infrared (0.8–2.5 micron). The rest-frame near-infrared penetrates deeper into the BLR than the rest-frame optical band. We here present a detailed analysis of 65 local BAT-selected Seyfert (Sy) galaxies observed at Magellan/FIRE. Adding these to the near-infrared BAT AGN spectroscopic survey (BASS) database (mostly observed with the ESO VLT/Xsh), we study a total of 314 unique near-infrared spectra with ancillary spectral data in optical and X-ray. This is the largest statistical sample of local AGN with rest-frame near-infrared spectra. These observations allow us to 1) construct a statistical sample of AGN to assess the presence of correlations between f and AGN properties, 2) build a more complete and less biased sample of AGN, by considering also Sy 1.8-1.9-2 with broad lines in the near-infrared, and 3) verify systematics in BLR characterisation (broad-line FWHM and luminosity and hence Mbh) as a function of X-ray obscuration and dust extinction.