Glimmering in the Dark: Modeling the Low-mass End of the M_•–σ Relation and of the Quasar Luminosity Function

Abstract

The M • − σ relation establishes a connection between central black holes (BHs) and their host spheroids. Supported by observations at M • 10 5 M , there is limited data on its validity at lower masses. Employing a semi-analytical model to simulate the combined evolution of BHs and their host galaxies, we predict the observational consequences of assuming a bimodality in the accretion efficiency of BHs, with low-mass BHs (M • 10 5 M ) accreting inefficiently. We predict a departure from the M • − σ relation at a transitional BH mass ∼ 10 5 M , with lower-mass BHs unable to reach the mass dictated by the relation and becoming disconnected from the evolution of the host galaxy. This prediction is an alternative to previous works suggesting a flattening of the relation at ∼ 10 5 − 10 6 M . Furthermore, we predict a deficit of BHs shining at bolometric luminosities ∼ 10 42 erg s −1 . Joined with a detection bias, this could partly explain the scarce number of intermediate-mass BHs detected. Conversely, we predict an increase in source density at lower bolometric luminosities, < 10 42 erg s −1 . Because our predictions assume a bimodal population of high-redshift BH seeds, future observations of fainter BHs will be fundamental for constraining the nature of these seeds.

Radio jets from AGNs in dwarf galaxies in the COSMOS survey: mechanical feedback out to redshift ∼3.4

“…Jiang et al 2011;Mezcua 2017;Shankar et al 2019) would be consistent with the predictions from models of direct collapse formation of seed BHs (e.g. Volonteri & Natarajan 2009;van Wassenhove et al 2010; but see Ricarte & Natarajan 2018) or could be ascribed to a bimodality in the accretion efficiency of BHs in which low-mass BH accrete inefficiently (Pacucci et al 2018), while a steepening at low stellar masses (e.g. Graham & Scott 2015;Davis et al 2018) would imply that the radio AGN dwarf galaxies have all BH masses ≤ 10 3 M .…”

“…Kormendy & Ho 2013). Alternatively, the change of slope at the low-mass end of the scaling relations could be also attributed to a bimodality in the accretion efficiency of seed BHs (Pacucci et al 2018).…”

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

“…These findings instead lend further support to the presence of a strong bias in the local quiescent black hole sample, possibly caused by the limited telescope resolution power that artificially increases the normalization of the σ-Mstar relation along with other scalings (e.g., Bernardi et al 2007;Shankar et al 2016Shankar et al , 2017. This bias has important consequences on a number of fronts, from implications for seeds and intermediate mass black holes (e.g., Graham 2016;Shankar et al 2016;Mezcua 2017;Pacucci et al 2018), gravitational waves (e.g., Sesana et al 2016;Taylor et al 2017;Chen et al 2018;Joshi et al 2018), to radiative/kinetic efficiencies (Shankar et al 2019, submitted). Reines & Volonteri (2015) pointed out that the quiescent subsample of later-type galaxies, especially pseudobulges, with dynamically-measured black holes tend to overlap with the black hole scaling relations in active galaxies.…”

The MBHBM⋆ Project. I. Measurement of the Central Black Hole Mass in Spiral Galaxy NGC 3504 Using Molecular Gas Kinematics

“…Apart from 11 M BH measurements in spiral MW-like galaxies from water masers (Greene et al 2016;Gao et al 2017;Zhao et al 2018), recent progress in the stellar/ionized gas dynamics and the virial M BH estimate techniques have lead to the detections of 28 sub-million Solar masses BHs in the sub-M ⋆ sample, whose M BH are a remarkably tiny fractions of the galaxy stellar masses (Seth et al 2010;Reines et al 2013;Baldassare et al 2015;den Brok et al 2015;Chilingarian et al 2018, N17, N18, N19), suggesting that these objects fall below the M BH -M bulge relation extrapolated from higher mass galaxies in a wide range of 1-3 orders of magnitude of M BH (N19). Many hypotheses have been proposed to explain this change that may be due to (i) the formation history of the bulge (Kormendy & Bender 2012;Krajnović et al 2018), (ii) the star formation history (SFH) of the galaxy (Caplar et al 2015;Terrazas et al 2017), or (iii) the bimodality of accretion efficiency of SMBH seeds (Pacucci et al 2015;Inayoshi & Haiman 2016;Park et al 2016;Pacucci et al 2017Pacucci et al , 2018a.…”