Evidences of merging in the Seyfert galaxy NGC 3393 revealed by modelling the spectra

TL;DR

This study uses spectral modeling to find evidence of galaxy merging in NGC 3393, revealing shock-induced gas compression, altered metallicity, and possible star formation triggered by collision.

Contribution

It provides new spectral evidence and analysis of shock effects and metallicity changes indicating galaxy merging in NGC 3393.

Findings

Higher preshock densities in NGC 3393's NLR compared to other AGN.

Metallicity around 0.78 solar, with signs of external matter mixing.

Potential formation of Wolf-Rayet stars due to galaxy collision.

Abstract

The discovery of two active black holes in the Seyfert galaxy NGC 3393, separated by about 490 light years, revealed a merging event. This led us to look for other evidences of galaxy collision and merging through the analysis of the observed spectra in different frequency ranges. We found preshock densities higher by a factor of about 10 in the NGC 3393 NLR than in other AGN and patches of ionized matter beyond the observed NLR bulk. They can be explained by compression and heating of the gas downstream of shock waves created by collision. Metallicity in terms of the O/H relative abundance, is about 0.78 solar. Mg/H depletion by a factor of about 3 compared with solar cannot be explained by Mg trapping into dust grains, due to rather high shock velocities. The low O/H and Mg/H abundances indicate mixing with external matter during collision. Twice solar N/H is predicted by modelling the spectra of high shock velocity clouds reached by a Ts =8.6 10^4 K black-body flux. This suggests that Wolf-Rayet stars could be created by galaxy collision in the central region.