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 (M bh ) may suffer from an angular resolution-related selection effect, which could bias the observed scaling relations between M bh and host galaxy properties away from the intrinsic relations. In particular, previous work has shown that the observed M bh -M star relation is more strongly biased than the M bh -σ relation. Local samples of active galactic nuclei (AGN) do not suffer from this selection effect, as in these samples M bh is estimated from megamasers and/or reverberation mapping-based techniques. With the exception of megamasers, M bh -estimates in these AGN samples are proportional to a virial coefficient f vir . Direct modelling of the broad line region suggests that f vir ∼ 3.5. However, this results in a M bh -M star 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 M bh -σ relation. Matching the high-mass end of the M bh -M star and M bh -σ relations observed in quiescent samples requires f vir 15 and f vir 7, respectively. On the other hand, f vir ∼ 3.5 yields M bh -σ and M bh -M star 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 M bh -M star scaling relation of AGN is driven by σ, thus providing additional key constraints to black hole-galaxy co-evolution models.

Revealing Hidden Substructures in the MBH–σ Diagram, and Refining the Bend in the L–σ Relation

“…The various curves in Figure 15 represent the major morphological types. Their layering suggests that the apparent offset between galaxies with and without a directly measured black hole mass, as observed by Shankar et al (2016Shankar et al ( , 2019, could simply be a reflection of the difference in the dominant morphological type in each sample. However, this is not conclusive and further investigation is required as their may yet be a selection bias or a discrepancy in the way that velocity dispersions are measured.…”

“…Their claim is based on the offset they observed in the velocity dispersion versus galaxy stellar 16 Including NGC 1300 in the regression changes the slope to 1.88 ± 0.48. mass diagram (σ-M ST AR , their Figure-1), between several samples of local ETGs with dynamically measured SMBH masses and a larger data-set of galaxies from Data Release-7 of the Sloan Digital Sky Survey (SDSS, York et al 2000;Abazajian et al 2009). This is restated in Shankar et al (2019) with a slight change in their galaxy stellar masses based on the SDSS data they used. Shankar et al (2016) suggest that the offset they obtain is a consequence of a sample selection effect in which galaxies with low-mass BHs are excluded because it is not possible to resolve their spheres-of-influence due to technological limitations.…”

“…In the right-hand panel of Figure 15, we also include the brown curve for late spiral galaxies (P (Scd) ≥ 0.7) from Shankar et al (2019, see the left panel in their Figure 1), which lies below the relation defined by our predominantly early spiral galaxies (Sa-Sb), simply referred to as LTGs in this paper. The various curves in Figure 15 represent the major morphological types.…”

Black hole feedback and the evolution of massive early-type galaxies

“…This not only limits the number of objects feasibly studied but also might introduce biases in the analysis (e.g. Shankar et al 2019). In order to provide a coherent and comprehensive observational picture, it is then necessary to investigate alternative metrics that do not require direct black hole mass measurements.…”

“…Finally, the mapping between black hole mass and σ might change with galaxy mass (e.g. Krajnović et al 2018;Shankar et al 2019) and even with redshift. Thus, interpreting trends as a function of galaxy or halo mass might lead to biased results (Bernardi et al 2007).…”