Evolution of Supermassive Black Hole Mass and their Accretion Rates Across the Last 10 Billion Years*

Supermassive black holes (SMBHs) reside at the centers of nearly all galaxies, yet their growth and appearance vary depending on their intrinsic properties and our viewing perspective. A central question is what regulates the distribution of gas and dust around these black holes. Studies in the local Universe suggest that accretion rate—the rate at which a black hole consumes matter—is the dominant factor. In this work, we extend this investigation to earlier cosmic times to test whether this trend persists throughout SMBH evolution. We analyze a sample of 2,293 X-ray–selected SMBHs from the Stripe82X survey, for which spectroscopic black hole masses and obscuration estimates are available. Using Bayesian Markov Chain Monte Carlo modeling, we trace the evolution of mass and accretion rate distributions over the past 10 billion years (z ≲ 2). Our results show that while high- and low-mass SMBHs exhibit similar accretion locally, low-mass SMBHs grow faster at earlier times, hinting at a mass-dependent growth history. These findings provide new insights into how SMBHs of different masses assembled their mass and powered active galaxies across cosmic time, helping to illuminate the long-term evolution of black hole populations.