The outflow impacts on the size of the narrow-line region among type-2 AGNs

TL;DR

This study investigates how outflows influence the size of narrow-line regions in type-2 AGNs, finding that NLR size correlates with AGN luminosity and is unaffected by outflow presence, highlighting photoionization as the key factor.

Contribution

The paper introduces a broadband imaging method to measure NLR sizes and demonstrates that outflows do not impact NLR extent, emphasizing photoionization as the primary driver.

Findings

NLR size correlates strongly with AGN luminosity.

Outflows do not significantly affect NLR size.

NLR size is primarily determined by photoionization.

Abstract

We present the study of the gas kinematics in narrow-line regions (NLRs) of 2,009 type-2 AGNs at $z<0.34$. We construct the [O III]$\lambda$5007 emission-line images using publicly available broadband images from the Sloan Digital Sky Survey (SDSS). The [O III] emission area of the samples, measured down to $1.4\times10^{-15}$ erg/s/cm$^2$/arcsec$^2$, ranges from 3.7 kpc$^2$ up to 224 kpc$^2$. With our broadband technique, we found the strong correlation between [O III] area and AGN luminosity inferred from the [O III] luminosity and the mid-infrared luminosity at the rest-frame $15\mu$m. The isophotal threshold used to determine the [O III] area affects the correlation strength in that the brighter isophote yields the stronger correlation between the [O III] area and AGN luminosity. The presence of gas outflow is examined by the ratio of the [O III] velocity dispersion to the stellar velocity dispersion ($\sigma_{\rm [O\,III]}/\sigma_\star > 1.4$) using the SDSS spectra. At the given luminosity, the objects with and without outflows exhibit the same extension of the [O III] emission. Their correlation between the [O III] area and luminosity is almost identical. It is suggested that the size of NLRs is not affected by outflow mechanisms but rather by photoionization from the central AGNS.