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Infrared spectroscopy of a Cygnus A - Implications for the obscured active nucleusNear-infrared spectroscopic observations of the central regions of the luminous radio galaxy Cygnus A are presented and interpreted in terms of an obscured quasar nucleus. Strong emission is detected in the molecular hydrogen lines 1-0 S(1) and 1-0 S(3), the strengths of which are accounted for through heating by the nuclear hard X-ray source. The large equivalent widths of these molecular hydrogen lines and the near-infrared narrow hydrogen recombination lines suggest that the observed nuclear continuum is strongly attenuated at 2 microns. The observed upper limit to the flux of broad Pa-alpha implies an extinction to the putative broad line region AV(BL) of at least 24 mag, and the observed continuum intensity of the nuclear point source at 2.2 microns gives an extinction of 43 +/-9 mag toward the optical-infrared continuum. These estimates are consistent with the gas column density inferred from the low-energy X-ray cutoff. Strong forbidden Si VI 1.962-micron line emission from Cygnus A is also reported.
Document ID
19920030864
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Ward, Martin J. (Oxford, University United Kingdom)
Blanco, Philip R. (Edinburgh, University United Kingdom)
Wilson, Andrew S. (Maryland, University College Park, United States)
Nishida, Minoru (Kyoto University Japan)
Date Acquired
August 15, 2013
Publication Date
November 20, 1991
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 382
ISSN: 0004-637X
Subject Category
ASTROPHYSICS
Funding Number(s)
CONTRACT_GRANT: NSF AST-87-19207
CONTRACT_GRANT: NAG5-1079
Distribution Limits
Public
Copyright
Other