Shinshu University

The University of Tokyo Graduate School of Science

Tokyo University of Science

Summary

Galactic nuclei (quasars) in the distant universe emit strong ultraviolet radiation, which ionizes hydrogen gas (intergalactic gas) around the galaxy. If the ultraviolet radiation is isotropic, the ionization level of the gas around a galaxy should be constant regardless of its direction. However, previous studies have reported that the ionization level is biased.

In this study, we investigated the cause of this bias by targeting a special object called a "BAL quasar," for which the direction of ultraviolet radiation can be estimated to some extent. In addition to existing data, new observations with the Subaru Telescope revealed that a doughnut-shaped shielding structure (dust torus) inside the quasar is most likely responsible for the anisotropic ionization level. The dust torus is an essential structure in the standard (unified) model of quasars. The results provide observational support for the existence of dust toruses and suggest that their effects may extend to the distant intergalactic gas.

The results of this study were published in the Astrophysical Journal, the journal of the American Astronomical Society, on July 19, 2022. This research was led by Shinshu University (Institute for Global Education), together with researchers from the Graduate School of Science of the University of Tokyo, The University of Tokyo, and Saitama University.

Note that graduate students Rikako Ishimoto and Professor Nobunari Kashiwagawa of the Department of Astronomy participated in this research.

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