Physical conditions in the Seyfert galaxy NGC 2992

This paper presents long-slit spectral maps of the bicone-shaped extended n arrow-line region (ENLR) in the Seyfert galaxy NGC 2992. We investigate the physical properties of the ENLR via emission-line diagnostics and compare the observations to shock and photoionization models for the excitation mec hanism of the gas. The line ratios vary as a function of position in the EN LR, and the loci of the observed points on line ratio diagrams are shown to be most consistent with shock + precursor model grids. We consider the ene rgetics of a nuclear ionizing source for the ENLR and perform the q-test in which the rate of ionizing photons from the nucleus is inferred from measu rements of the density and ionization parameter. The q-test is shown to be invalid in the case of NGC 2992 because of the limitations of the [S II] la mbda 6717/lambda 6731 density diagnostic. The excitation of the gas is show n to be broadly consistent with the kinematics? with higher [N II] lambda 6 583/H alpha present in the more dynamically active region. We also show tha t the pressure associated with the X-ray-emitting plasma may provide a larg e fraction of the pressure required to power the ENLR via shocks.