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Radiative excitation of molecules near powerful compact radio sources

1994; IOP Publishing; Volume: 432; Linguagem: Inglês

10.1086/174599

1538-4357

Philip R. Maloney, Mitchell C. Begelman, M. J. Rees,

Astronomy and Astrophysical Research

view Abstract Citations (32) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiative Excitation of Molecules near Powerful Compact Radio Sources Maloney, Philip R. ; Begelman, Mitchell C. ; Rees, Martin J. Abstract In a recent paper, Barvainis & Antonucci searched for and failed to detect CO J = 1-0 absorption from the obscuring torus in the nearby powerful radio galaxy Cygnus A. We show that a plausible explanation for the lack of absorption (assuming that the ionization parameter within the torus is low enough for the gas to be molecular) is that radiative excitation of the CO molecules by the nonthermal radio continuum increases the excitation temperature of the lower rotational levels substantially, reducing the optical depths. The excitation temperature may approach the brightness temperature of the radio source at high enough flux-to-density ratios. Heating of the gas by the nonthermal excitation may also be important. We discuss the region of parameter space in which this excitation mechanism will be important and the implications for observations of obscuring tori. Subject headings; galaxies: active - galaxies: individual (Cygnus A) - galaxies: ISM - molecular processes - radio continuum: galaxies Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174599 Bibcode: 1994ApJ...432..606M Keywords: Active Galactic Nuclei; Emission Spectra; Gas Heating; Interstellar Matter; Molecular Excitation; Radio Emission; Radio Galaxies; Brightness Temperature; Carbon Monoxide; Rotational States; Toruses; Astrophysics; GALAXIES: ACTIVE; GALAXIES: ISM; RADIO CONTINUUM: GALAXIES; MOLECULAR PROCESSES; GALAXIES: INDIVIDUAL NAME: CYGNUS A full text sources ADS | data products SIMBAD (1) NED (1)