Diagnostics of ionized gas in galaxies with the "BPT--radial velocity dispersion" relation

TL;DR

This paper introduces a new diagnostic method combining emission line fluxes and velocity dispersion to better understand ionization sources in galaxy gas, revealing correlations with shock excitation and cloud collisions.

Contribution

The study develops the 'BPT--sigma relation' by integrating velocity dispersion into classical diagnostics, enhancing the identification of ionization mechanisms in galactic gas.

Findings

Positive correlation between velocity dispersion and shock excitation contribution.

Confirmation of cloud collisions in Arp 212 via BPT-sigma relation.

Method applied to multiple galaxies with diverse gas dynamics.

Abstract

In order to study the state of gas in galaxies, diagrams of the relation of optical emission line fluxes are used allowing one to separate main ionization sources: young stars in the H II regions, active galactic nuclei, and shock waves. In the intermediate cases, when the contributions of radiation from OB stars and from shock waves mix, identification becomes uncertain, and the issue remains unresolved on what determines the observed state of the diffuse ionized gas (DIG) including the one on large distances from the galactic plane. Adding of an extra parameter - the gas line-of-sight velocity dispersion - to classical diagnostic diagrams helps to find a solution. In the present paper, we analyze the observed data for several nearby galaxies: for UGC 10043 with the galactic wind, for the star forming dwarf galaxies VII Zw 403 and Mrk 35, for the galaxy Arp 212 with a polar ring. The data on the velocity dispersion are obtained at the 6-m SAO RAS telescope with the Fabry-Perot scanning interferometer, the information on the relation of main emission-line fluxes - from the published results of the integral-field spectroscopy (the CALIFA survey and the MPFS spectrograph). A positive correlation between the radial velocity dispersion and the contribution of shock excitation to gas ionization are observed. In particular, in studying Arp 212, "BPT-sigma relation" allowed us to confirm the assumption on a direct collision of gaseous clouds on the inclined orbits with the main disk of the galaxy.