STScI Preprint #1329
We consider a model in which the narrow line regions (NLRs) of Seyfert galaxies are photoionized "in situ" by fast (300-1,000 km s-1), radiative shock waves driven into the interstellar medium of the galaxy by radio jets from the active nucleus. Such shocks are powerful sources of soft X-rays. We compute the expected ratio of the count rates in the ROSAT PSPC and Einstein IPC detectors to the [OIII] 5007 flux as a function of shock velocity, and compare these ratios with observations of type 2 Seyferts. If most of the observed soft X-ray emission from these galaxies originates in the NLR and the absorbing hydrogen column is similar to that inferred from the reddening of the NLR, a photoionizing shock model with shock velocity
400-500 km s-1 is compatible with the observed ratios. High angular resolution observations with AXAF are needed to isolate the X-ray emission of the NLR and measure its absorbing column, thus providing a more conclusive test. We also calculate the expected coronal iron line emission from the shocks. For most Seyfert 2s, the [Fe X]
ratio is a factor of 2-14 lower than the predictions of 300-500 km s-1 shock models, suggesting that less hot gas is present than required by these models.
1) Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
2) Also Astronomy Department, University of Maryland, College Park, MD 20742
3) Harvard-Smithsonian Center for Astrophysics 60 Garden Street Cambridge, MA 02138