Running Late: Exploring the Delayed Supermassive Black Hole Growth Seen by Hydro-Dynamical Simulations

Abstract

Despite the vast amount of processes that depend on the co-evolution of supermassive black holes (SMBHs) and their host galaxies, their physical relationship is still not fully understood. Observations have revealed a well-constrained scaling relation between SMBH mass and galaxy bulge mass in the local universe. In galaxy formation simulations, a different form of SMBH growth behavior emerges at high redshift: prolonged slow growth in the early universe followed by coherent fueling that results in a rapid increase in the central BH's mass. After this "catch-up" period of rapid growth, the SMBH growth resembles the well documented observed local scaling relation between SMBH mass and galaxy bulge mass. We conduct an in-depth study of these SMBH growth behaviors to explore implications it has on the early universe scaling relation. We construct a simple model, using said behaviors, to predict the quasar luminosity function which can be compared to well-documented observable quantities. To combine the simulation behaviors with a mock catalog of galaxies, we employ mathematical convolution techniques. This involves numerical integration methods over a population of dark matter halos and various models that relate the dark matter halo population to quasar luminosity. The models this study produces to resemble the simulation behaviors contains three free parameters. Thus, we employ a least squares fit method on a three dimensional parameter space to find the free parameters that best fit the predictions of our study to various observational data. These results allow us to systematically quantify the range of allowed scenarios for the emergence of the scaling relation between SMBH mass and galaxy bulge mass observed in the local universe.