利用次毫米陣列研究天鵝座A超大質量黑洞之吸積流

Abstract

測量超大質量黑洞鄰近之吸積率，可以由觀測上給出對於吸積流模型之限制，也能探討相對論性噴流的動力機制。此論文聚焦於低亮度活躍星系核(low-luminosity active galactic nuclei)，其低亮度被視為是由於其超大質量黑洞之吸積流為低輻射效率。藉由次毫米波陣列望遠鏡測量了天鵝座A 之核心在毫米波段之偏振輻射。在此觀測中，基於天鵝座A 之偏振性質在統計上缺乏有效之測量值，藉由去偏振化機制、軔致輻射吸收之探討及半解析平流主導吸積流光譜能量分佈之擬和，計算出旋轉量(rotation measure)、吸積率(the mass accretion)、以及吸積功率(accretion power) 之觀測下限值。並由此觀測得到排除對流主導吸積流模型之結論。

Unveiling the nature of accretion process onto the supermassive black hole (SMBH) is one of the primary purposes in modern high energy astrophysics. Constraining mass accretion rate (M ̇ ) can not only clarify the features of in- flow but also connect to the dynamics of outflow. In this dissertation, we concentrate on the low-luminosity active galactic nuclei (LLAGN) of Cygnus A, which are thought to be powered by radiatively inefficient accretion flow (RIAF). Faraday rotation measure (RM), the tracer of plasma density, pro- vides a powerful tool that can be used to investigate the mass accretion rate near the SMBH of LLAGN. We present the polarimetric observation results towards Cygnus A utilizing Submillimeter Array at 230 GHz and obtain the observational constraint on RM. With the scenarios of beam/bandwidth de- polarization and advection-dominated accretion flow model fitting, the mass accretion rate and the accretion type of Cygnus A can be constrained, and the convection-dominated accretion flow solution is excluded.