Searching for an Intermediate Mass Black Hole in the Blue Compact Dwarf galaxy MRK 996

TL;DR

This study investigates whether an intermediate mass black hole in galaxy MRK 996 contributes to its ionisation, finding that shocks from supernovae and stellar winds are more likely responsible for observed ionisation features.

Contribution

The paper provides tight X-ray luminosity and black hole mass limits, and demonstrates that shocks, not an intermediate mass black hole, explain the galaxy's ionisation features.

Findings

X-ray luminosity upper limit is too low to support an active black hole.

Shocks from supernovae and stellar winds likely cause the observed ionisation.

Diffuse X-ray emission is consistent with shock heating of the interstellar medium.

Abstract

The possibility is explored that accretion on an intermediate mass black hole contributes to the ionisation of the interstellar medium of the Compact Blue Dwarf galaxy MRK996. Chandra observations set tight upper limits (99.7 per cent confidence level) in both the X-ray luminosity of the posited AGN, Lx(2-10keV)<3e40erg/s, and the black hole mass, <1e4/\lambda Msolar, where \lambda, is the Eddington ratio. The X-ray luminosity upper limit is insufficient to explain the high ionisation line [OIV]25.89\mu m, which is observed in the mid-infrared spectrum of the MRK996 and is proposed as evidence for AGN activity. This indicates that shocks associated with supernovae explosions and winds of young stars must be responsible for this line. It is also found that the properties of the diffuse X-ray emission of MRK996 are consistent with this scenario, thereby providing direct evidence for shocks that heat the galaxy's interstellar medium and contribute to its ionisation.