Probing the Physics of Narrow Line Regions in Active Galaxies III: Accretion and Cocoon Shocks in the LINER NGC1052

TL;DR

This study uses integral field and HST spectroscopy to analyze the LINER galaxy NGC 1052, proposing a double shock model involving accretion and cocoon shocks to explain its emission line properties and outflows.

Contribution

It introduces a novel double shock model combining accretion and cocoon shocks to explain LINER galaxy emission lines and outflow features.

Findings

Identification of a turbulent accretion disk in NGC 1052

Detection of a large-scale outflow and ionisation cone

Modeling of emission lines with a double shock scenario

Abstract

We present Wide Field Spectrograph (WiFeS) integral field spectroscopy and HST FOS spectroscopy for the LINER galaxy NGC 1052. We infer the presence of a turbulent accretion flow forming a small-scale accretion disk. We find a large-scale outflow and ionisation cone along the minor axis of the galaxy. Part of this outflow region is photoionised by the AGN, and shares properties with the ENLR of Seyfert galaxies, but the inner ($R \lesssim 1.0$~arcsec) accretion disk and the region around the radio jet appear shock excited. The emission line properties can be modelled by a "double shock" model in which the accretion flow first passes through an accretion shock in the presence of a hard X-ray radiation, and the accretion disk is then processed through a cocoon shock driven by the overpressure of the radio jets. This model explains the observation of two distinct densities ($\sim10^4$ and $\sim10^6$ cm$^{-3}$), and provides a good fit to the observed emission line spectrum. We derive estimates for the velocities of the two shock components and their mixing fractions, the black hole mass, the accretion rate needed to sustain the LINER emission and derive an estimate for the jet power. Our emission line model is remarkably robust against variation of input parameters, and so offers a generic explanation for the excitation of LINER galaxies, including those of spiral type such as NGC 3031 (M81).