Supercritical dusty BH growth in the early Universe

Abstract

Supermassive black holes (with $\mathrm{M_{BH} \sim 10^9 M_{\odot}}$) are observed in the first Gyr of the Universe, and their host galaxies are found to contain unexpectedly large amounts of dust and metals. In light of the two empirical facts, we explore the possibility of supercritical accretion and early black hole growth occurring in dusty environments. We generalise the concept of photon trapping to the case of dusty gas and analyse the physical conditions leading to dust photon trapping. Considering the parameter space dependence, we obtain that the dust photon trapping regime can be more easily realised for larger black hole masses, higher ambient gas densities, and lower gas temperatures. The trapping of photons within the accretion flow implies obscured active galactic nuclei (AGNs), while it may allow a rapid black hole mass build-up at early times. We discuss the potential role of such dust photon trapping in the supercritical growth of massive black holes in the early Universe.