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Spectroscopy of the near-nuclear regions of Cygnus A: estimating the mass of the supermassive black hole

By C. Tadhunter, A. Marconi, D. Axon, K. Wills, T. G. Robinson and N. Jackson


We use a combination of high spatial resolution optical and near-IR spectroscopic data to make a detailed study of the kinematics of the NLR gas in the near-nuclear regions of the powerful, FRII radio galaxy Cygnus A (z = 0.0560), with the overall goal of placing limits on the mass of any supermassive black hole in the core. Our K-band infrared observations (0.75 arcsec seeing) – taken with NIRSPEC on the Keck II telescope – show a smooth rotation pattern across the nucleus in the Paα and H2 emission lines along a slit position (PA180) close to perpendicular to the radio axis, however, there is no evidence for such rotation along the radio axis (PA105). Higher spatial resolution observations of the [OIII]λ5007 emission line – taken with STIS on the Hubble Space Telescope (HST) – confirm the general rotation pattern of the gas in the direction perpendicular to the radio axis, and provide evidence for steep velocity gradients within a radius of 0.1 arcsec of the core — corresponding to the high surface brightness structure visible in high resolution narrow band images. The [OIII] line remains broad throughout the core region (FWHM ∼ 300 – 900 km s −1), but th

Year: 2003
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