New Research Central Black Hole's Impact on Galaxy's Cold Gas Content

TapTechNews August 15th news, today (August 15th) the official WeChat public account of Nanjing University released a blog post announcing that its team's latest research has for the first time provided direct evidence from observations of the influence of the central black hole of the galaxy on the cold gas content.

Half a century's mystery

A galaxy is the basic unit that makes up the universe. Taking our Milky Way as an example, a galaxy is a self-gravitationally bound system that contains hundreds of billions of stars, interstellar media such as gas and dust, and a central supermassive black hole.

The internal components of the galaxy and the circumgalactic medium around it have complex interactions on multiple spatial and temporal scales, jointly affecting the formation and evolution of the galaxy.

Astronomers generally divide galaxies into two types: one is relatively young galaxies that are still actively generating new stars, called star-forming galaxies; while the other is relatively old galaxies that have almost no new star formation, called passive evolving galaxies.

After nearly half a century of development, it has become a common conclusion in the current mainstream galaxy formation and evolution theoretical models that the central black hole has an important feedback effect on the host galaxy. However, there has been a lack of clear evidence in observations on whether and how the black hole affects the formation and evolution of the galaxy.

Research team introduction

Professor Wang Tao from Nanjing University is the first author and corresponding author of the paper, and two graduate students, Xu Ke and Wu Yuxuan from Nanjing University, have made important contributions to the paper. Professor Shi Yong, Professor Gu Qiusheng, Professor Zhang Zhiyu, Associate Professor Wang Yijun from Nanjing University, and relevant researchers from the French Atomic Energy Institute, Peking University, Shanghai Normal University, Tianjin Normal University, and Fudan University participated in this work.

This work has received support from the National Natural Science Foundation of China, the National Key R & D Program, and the manned spaceflight project.

Research results

In 2009, Wang Tao went to the Harvard-Smithsonian Center for Astrophysics in the United States for further study. Since then, he has been committed to studying the problem of how galaxies from birth to death.

Professor Wang Tao and his collaborators innovatively started from exploring the relationship between the black hole mass of nearby galaxies and the atomic hydrogen gas content in the galaxy, and for the first time revealed that the mass of the central black hole of the galaxy is the most critical physical quantity that modulates the atomic hydrogen gas content in the galaxy: the higher the mass of the central black hole, the lower the atomic hydrogen gas content.

Atomic hydrogen gas is the main component of the galaxy's cold gas, and cold gas is the raw material for star formation in the galaxy. Therefore, this discovery provides important observational evidence for whether and how the central black hole affects the cold gas content and star formation in the galaxy.

Wang Tao explained:

If the black hole accretes and pushes out the cold gas, there will be a process of a rapid decrease in the cold gas content in a short time.

In previous studies, even in those host galaxies with the most active black holes, there is no such process. This indicates that it is very likely that the second way dominates.

And atomic hydrogen gas in the galaxy is the direct product of the cooling of hot gas, so we turn our attention to the connection between atomic hydrogen gas and the black hole.

This work also simultaneously reveals that different types of galaxies follow the same cold gas content-black hole mass relationship (Figure 1), which means that the cold gas content-black hole mass relationship provides a new and possibly more fundamental framework for studying the formation and evolution of galaxies, especially for studying the transformation mechanism between different types of galaxies.

Significance

This result also places important constraints on the specific feedback mechanism of the central black hole on the host galaxy. Because atomic hydrogen gas is the primary product of the cooling of the circumgalactic gas, this discovery implies that regulating the cooling efficiency of the circumgalactic gas through the energy released during the growth of the central black hole is likely the main way for the central black hole to affect the formation and evolution of the host galaxy.

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