BASS. XXXV. Stellar vel. dispersion of type 1 AGNs

We present two independent measurements of stellar velocity dispersions ({sigma}*) from the CaII H+K {lambda}3969,3934 and MgIb{lambda}5183,5172,5167 region (3880-5550{AA}) and the calcium triplet region (8350-8750{AA}) for 173 hard X-ray-selected Type 1 active galactic nuclei (AGNs; z<=0.08) from the 105 month Swift-BAT catalog. We construct one of the largest samples of local Type 1 AGNs that have both single-epoch virial black hole mass (M_BH_) estimates and {sigma}* measurements obtained from high spectral resolution data, allowing us to test the usage of such methods for supermassive black hole studies.

We find that the two independent {sigma}* measurements are highly consistent with each other, with an average offset of only 0.002+/-0.001dex. Comparing MBH estimates based on broad emission lines and stellar velocity dispersion measurements, we find that the former is systematically lower by ~0.12dex. Consequently, Eddington ratios estimated through broad-line MBH determinations are similarly biased (but in the opposite way).