Probing the Hot X-Ray Gas in the Narrow-line Region of Mrk 3

We study the prototypical Seyfert 2 galaxy, Markarian 3, based on imaging and high-resolution spectroscopy observations taken by Chandra. We construct a deconvolved X-ray image, which reveals the S-shaped morphology of the hot gas in the narrow-line region (NLR). While this morphology is similar to the radio and [O iii] emission, the distribution of the X-ray gas is broader than that obtained at these other wavelengths. By mapping the density and temperature distribution of the hot gas in the NLR, we demonstrate the presence of shocks toward the west ($M={2.5}_{-0.6}^{+1.0}$) and east ($M={1.5}_{-0.5}^{+1.0}$). Moreover, we compute the flux ratios between the [O iii] and 0.5–2 keV band X-ray luminosity and show that it is nonuniform in the NLR, with the western side of the NLR being more highly ionized. In addition, based on the Chandra grating data, we investigate the line ratios of the Si xiii triplet, which are not consistent with pure photoionization. Based on these results, we suggest that in the NLR of Mrk 3 both photoionization and collisional ionization act as excitation mechanisms. We conclude that the canonical picture, in which photoionization is solely responsible for exciting the interstellar medium in the NLR of Seyfert galaxies, may be overly simplistic. Given that weak and small-scale radio jets are commonly detected in Seyfert galaxies, it is possible that shock heating plays a non-negligible role in the NLR of these galaxies.