http://arxiv.org/abs/1808.09452
The $M_{\bullet} – \sigma$ relation establishes a connection between central black holes (BHs) and their host spheroids. Supported by observations at $M_{\bullet} \gtrsim 10^5 \, M_{\odot}$, 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 ($M_{\bullet} \lesssim 10^5 \, M_{\odot}$) accreting inefficiently. We predict a departure from the $M_{\bullet} – \sigma$ relation at a transitional BH mass $\sim 10^5 \, M_{\odot}$, 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 $\sim 10^5-10^6 \, M_{\odot}$. Furthermore, we predict a deficit of BHs shining at bolometric luminosities $\sim 10^{42} \, \mathrm{erg \, s^{-1}}$. 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, $<10^{42} \, \mathrm{erg \, s^{-1}}$. 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.
F. Pacucci, A. Loeb, M. Mezcua, et. al.
Thu, 30 Aug 18
51/61
Comments: Published in ApJ Letters, 2018 September 1. Published version: 6 pages, 3 figures