New study reveals evolutionary paths of supermassive black holes and host galaxies

A recent paper titled “The Co-Evolution of Supermassive Black Holes and Their Host Galaxies,” published in the August 17, 2023 issue of Nature Astronomy, sheds new light on the intricate relationship between supermassive black holes and the galaxies they reside in.

This research was carried out by Dr. Ming-Yang Zhuang, who graduated from Peking University in 2022 and is currently affiliated with the University of Illinois Urbana-Champaign, in collaboration with Prof. Luis C. Ho from the Kavli Institute for Astronomy and Astrophysics at Peking University. They analyzed the structural and photometric properties of nearly 11,500 unobscured active galactic nuclei (AGNs) with redshifts of ≤ 0.35, using data from the Pan-STARRS1 3PI Steradian Survey. Their aim was to uncover the connections between the mass of black holes and the characteristics of their host galaxies in our nearby universe.

A longstanding puzzle in astronomy has been the observed correlations between supermassive black hole masses and properties of their host galaxies. However, there has been no consensus on the origins or evolution of these relationships. The specific connection between black hole mass and the properties of AGN host galaxies in the nearby universe has remained elusive.

The study revealed that galaxies with actively accreting black holes exhibit a consistent relationship between black hole mass and stellar mass, regardless of the type of galaxy. Furthermore, a galaxy’s position on this relationship appears to be linked to its level of star formation and black hole accretion activity.

Dr. Zhuang explains, “Our findings reveal the evolutionary paths for galaxies on the black hole mass-stellar mass plane. The co-evolution of galaxies and their central black holes seems to be synchronized over long periods. Galaxies with over-sized black holes compensate by producing more stars, while those with smaller black holes allow the black hole to consume more matter. Eventually, a balance is reached between the two.”

The presence of a common gas reservoir for both black hole accretion and star formation may explain the coordinated growth observed on this relationship. The evolutionary trajectory of galaxies with under-massive black holes, located below the relationship, supports a scenario proposed by recent simulations where black hole growth initially lags behind star formation but later catches up as the gas stabilizes at higher stellar masses. AGNs with over-massive black holes, positioned above the relationship, continue to accumulate stellar mass, consistent with active star formation and ample gas content in early-type AGN host galaxies.

These trajectories suggest that radiative-mode AGN feedback mechanisms, which were expected to suppress star formation, are less effective for galaxies below the scaling relation. Conversely, kinetic-mode feedback appears insufficient to halt long-term star formation in galaxies above the relationship.

Prof. Ho remarks, “This research provides fresh insights into the co-evolution of supermassive black holes and their host galaxies, serving as a foundational framework for future evolutionary studies. These findings offer crucial observational boundaries for numerical simulations aiming to model the intricate interplay between black holes and their host galaxies.”

The editor of Nature Astronomy states, “This article explores the evolutionary paths of galaxies on the black hole mass–stellar mass plane in the nearby universe, linking the properties of star formation and black hole accretion and providing critical constraints for active galactic nuclei feedback.”

A reviewer of the paper adds, “The discoveries presented in this paper are highly intriguing and hold significant importance for our comprehension of the co-evolution of black holes and galaxies throughout cosmic history, including their star formation and accretion processes.”

Source: Peking University

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