Low-Luminousity End of AGN Activities

Details Low-Luminousity End of AGN Activities Low-Luminousity End of AGN Activities

Feb 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sgyu.conf..179k&link_type=abstract

Studies of Galaxies in the Young Universe with New Generation Telescope, Proceedings of Japan-German Seminar, held in Sendai, Ja

Physics

Scientific paper

The essential ingredients of a central engine of active galactic nuclei (AGNs) are thought of as a supermassive black hole and an accretion disk surrounding it. It was once supposed that the presence of a supermassive black hole in a nucleus is the key point of its intensive activity. Recently, however, many evidences have clarified that there exists a supermassive black hole even at each nucleus of apparently-normal nearby galaxies. Since many of them show weak but AGN-like activities, they are often called the low-luminosity active galactic nuclei (LLAGNs). The simplest way of understanding the great difference in the luminosity scales of the nuclear activities between these categories is to regard it as a consequence of difference in the normalized mass accretion rate dot{m} ≡ dot{M}/dot{M}Edd. Namely, LLAGNs are understood as `starved' AGNs. Thus, the main problem may be to understand how differently the accretion disks can behave under different circumstances. As a promising model for such accretion disks under starved circumstances, we propose that of an optically thin ADAF (advection-dominated accretion flow) in a global magnetic field. The model contains winds from the surfaces of the disks and a physically important criterion for the generation of such winds can be derived from it. Recent observations of nuclear X-ray spectra of closest LLAGNs by Chandra satellite may pose fairly strong constraints on various models for such objects. We will therefore present some examples of our broadband spectral fitting for Sgr A* and M 31*.

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