Probing the hot X-ray gas in the narrow-line region of Mrk 3

TL;DR

This study uses Chandra X-ray observations to analyze the morphology, ionization mechanisms, and shock presence in the NLR of Mrk 3, revealing complex excitation processes beyond pure photoionization.

Contribution

It provides the first detailed high-resolution X-ray imaging and spectroscopy of Mrk 3's NLR, demonstrating the coexistence of photoionization and shock heating.

Findings

S-shaped hot gas morphology similar to radio and [O III] emission

Detection of shocks with Mach numbers 1.5-2.5 in the NLR

Non-uniform [O III]/X-ray flux ratios indicating varied ionization

Abstract

We study the prototypical Seyfert 2 galaxy, Markarian 3, based on imaging and high-resolution spectroscopy observations taken by the Chandra X-ray Observatory. 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 towards the west ($M=2.5^{+1.0}_{-0.6}$) and east ($M=1.5^{+1.0}_{-0.5}$). Moreover, we compute the flux ratios between the [O III] and $0.5-2$ keV band X-ray luminosity and show that it is non-uniform 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.