BASS. XXXV.: The MBH–σ* Relation of 105Month Swift-BAT Type 1 AGNs

Abstract

We present two independent measurements of stellar velocity dispersions (σå) from the Ca II H+K λ3969, 3934 and Mg I b λ 5183, 5172, 5167 region (3880–5550 Å) and the calcium triplet region (8350–8750 Å) 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 (MBH) estimates and σå 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 σå measurements are highly consistent with each other, with an average offset of only 0.002 ± 0.001 dex. Comparing MBH estimates based on broad emission lines and stellar velocity dispersion measurements, we find that the former is systematically lower by ≈0.12 dex. Consequently, Eddington ratios estimated through broad-line MBH determinations are similarly biased (but in the opposite way). We argue that the discrepancy is driven by extinction in the broad-line region. We also find an anticorrelation between the offset from the MBH–σå relation and the Eddington ratio. Our sample of Type 1 AGNs shows a shallower MBH–σå relation (with a power-law exponent of ≈3.5) compared with that of inactive galaxies (with a power-law exponent of ≈4.5), confirming earlier results obtained from smaller samples.