Black hole scaling relations of active and quiescent galaxies: Addressing selection effects and constraining virial factors

Abstract

Local samples of quiescent galaxies with dynamically measured black hole masses (Mbh) may suffer from an angular resolution-related selection effect, which could bias the observed scaling relations between Mbh and host galaxy properties away from the intrinsic relations. In particular, previous work has shown that the observed Mbh–Mstar relation is more strongly biased than the Mbh–σ relation. Local samples of active galactic nuclei (AGN) do not suffer from this selection effect, as in these samples Mbh is estimated from megamasers and/or reverberation mapping-based techniques. With the exception of megamasers, Mbh estimates in these AGN samples are proportional to a virial coefficient fvir. Direct modelling of the broad-line region suggests that fvir ∼ 3.5. However, this results in an Mbh–Mstar relation for AGN, which lies below and is steeper than the one observed for quiescent black hole samples. A similar though milder trend is seen for the Mbh–σ relation. Matching the high-mass end of the Mbh–Mstar and Mbh–σ relations observed in quiescent samples requires fvir ≳ 15 and fvir ≳ 7, respectively. On the other hand, fvir ∼ 3.5 yields Mbh–σ and Mbh–Mstar relations for AGN, which are remarkably consistent with the expected ‘intrinsic’ correlations for quiescent samples (i.e. once account has been made of the angular resolution-related selection effect), providing additional evidence that the sample of local quiescent black holes is biased. We also show that, as is the case for quiescent black holes, the Mbh–Mstar scaling relation of AGN is driven by σ, thus providing additional key constraints to black hole–galaxy co-evolution models.

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