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Session 50 - Active Galaxies.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center

[50.12] Shock Excited Gas in NGC 2992.

M. G. Allen (MSSSO/JHU), Z. Tsvetanov (JHU), M. A. Dopita (MSSSO)

We present evidence for the production of ionizing photons at the edges of the ionization bi-cone in the Seyfert 2 galaxy NGC 2992. This may be due to fast (250--500 km s^-1) radiative shocks where the powerful bipolar outflow interacts with the ISM.

NGC 2992 has a prominent bi-cone or double-bowl shaped Extended Emission Line Region (EELR) in [OIII] \lambda5007 and H\alpha+[NII] narrow band images. Previously measured kinematics show each side expanding with velocities up to 200 km s^-1. A grid of long-slit spectra covering most of the EELR was obtained with the DBS spectrograph on the MSSSO 2.3m Telescope at Siding Spring, Australia. The wavelength range includes lines from [OII]\lambda3727 to [SIII]\lambda9532 with 2.2--4.1 Åpix resolution. The grid of spectra allows the ionization parameter U and the electron density n_e to be measured independently at each grid point [regularly spaced at \sim2'' ( 300 pc, H_0=75 km s^-1 Mpc^-1 )] from emission line ratios.

The rate of ionizing photons Q required for a central source, inferred from U = Q/(4\pir^2n_ec) , shows enhancement at the edges of the bi-cone, and is relatively constant elsewhere. This suggests that while most of the EELR is illuminated by a central source, there is extra production of ionizing photons at the edges of the bi-cone. This effect is also apparent in the narrow band image excitation map. We will discuss the likely production of these photons by fast radiative shocks generated by the interaction of the strong wind with the ISM.

Program listing for Tuesday