2000MNRAS.318.1232W

We present J, H and K-band spectroscopy of Cygnus A, spanning 1.0-2.4µm in the rest-frame and hence several rovibrational H₂, H recombination and [Feii] emission lines. The lines are spatially extended by up to 6kpc from the nucleus, but their distinct kinematics indicate that the three groups (H, H₂ and [Feii]) are not wholly produced in the same gas. The broadest line, [Feii]λ1.644, exhibits a non-Gaussian profile with a broad base (FWHM≃1040km.s^–1), perhaps because of the interaction with the radio source. Extinctions to the line-emitting regions substantially exceed earlier measurements based on optical H recombination lines.

Hard X-rays from the quasar nucleus are likely to dominate the excitation of the H₂ emission. The results of Maloney, Hollenbach & Tielens are thus used to infer the total mass of gas in H₂ v=1-0 S(1)-emitting clouds as a function of radius, for gas densities of 10³ and 10⁵cm^–3, and stopping column densities N_H=10²²-10²⁴cm^–2. Assuming azimuthal symmetry, at least 2.3x10⁸M_☉ of such material is present within 5kpc of the nucleus, if the line-emitting clouds see an unobscured quasar spectrum. Alternatively, if the bulk of the X-ray absorption to the nucleus inferred by Ueno et al. actually arises in a circumnuclear torus, the implied gas mass rises to ∼10¹⁰M_☉. The latter plausibly accounts for 10⁹yr of mass deposition from the cluster cooling flow, for which {formmu1} within this radius.