STScI Preprint #1329

Do Jet-Driven Shocks Ionize the Narrow Line Regions of Seyfert Galaxies?

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]6374/H 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.

Status:

Appeared in: The Astrophysical Journal

Affiliations:

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