VLT MUSE observations of the bubble nebula around NGC 1313 X-2 and evidence for additional photoionization

TL;DR

This study uses MUSE observations to analyze the bubble nebula around NGC 1313 X-2, revealing that photoionization, alongside shock-ionization, significantly contributes to its emission, driven by the ULX and nearby stars.

Contribution

It provides new evidence that photoionization plays a crucial role in the nebula's ionization, complementing shock-ionization, based on spatial emission analysis and ionizing luminosity calculations.

Findings

Enhanced OIII emission coincides with star clusters and the ULX

Photoionization, not just shocks, explains emission line ratios

The ULX and massive stars supply sufficient ionizing luminosity

Abstract

The bubble nebula surrounding NGC 1313 X-2 is believed to be powered by high velocity winds from the central ultraluminous X-ray source (ULX) as a result of supercritical accretion. With the Multi-Unit Spectroscopic Explorer (MUSE) observation of the nebula, we find enhanced OIII emission at locations spatially coincident with clusters of stars and the central X-ray source, suggesting that photoionization in addition to shock-ionization plays an important role in powering the nebula. The X-ray luminosity of the ULX and the number of massive stars in the nebula region can account for the required ionizing luminosity derived with MAPPINGS V, which also confirms that pure shocks cannot explain the observed emission line ratios.