Associated molecular and atomic clouds with X-ray shell of superbubble 30 Doradus C in the LMC

TL;DR

This study investigates the connection between high-energy radiation and the interstellar medium in the superbubble 30 Doradus C, revealing interactions between molecular clouds, X-ray emissions, and cosmic-ray acceleration.

Contribution

The paper provides high-resolution ALMA observations of molecular clouds and links them to X-ray enhancements, advancing understanding of shock-cloud interactions and cosmic-ray acceleration in superbubbles.

Findings

X-ray emissions are enhanced toward molecular clouds.

X-ray enhancement correlates with total interstellar protons.

Cosmic-ray electrons are likely accelerated by supernovae.

Abstract

30 Doradus C is a superbubble which emits the brightest nonthermal X- and TeV gamma-rays in the Local Group. In order to explore detailed connection between the high energy radiation and the interstellar medium, we have carried out new CO and HI observations using the Atacama Large Millimeter$/$Submillimeter Array (ALMA), Atacama Submillimeter Telescope Experiment, and the Australia Telescope Compact Array with resolutions of up to 3 pc. The ALMA data of $^{12}$CO($J$ = 1-0) emission revealed 23 molecular clouds with the typical diameters of $\sim$6-12 pc and masses of $\sim$600-10000 $M_{\odot}$. The comparison with the X-rays of $XMM$-$Newton$ at $\sim$3 pc resolution shows that X-rays are enhanced toward these clouds. The CO data were combined with the HI to estimate the total interstellar protons. Comparison of the interstellar proton column density and the X-rays revealed that the X-rays are enhanced with the total proton. These are most likely due to the shock-cloud interaction modeled by the magnetohydrodynamical simulations (Inoue et al. 2012, ApJ, 744, 71). Further, we note a trend that the X-ray photon index varies with distance from the center of the high-mass star cluster, suggesting that the cosmic-ray electrons are accelerated by one or multiple supernovae in the cluster. Based on these results we discuss the role of the interstellar medium in cosmic-ray particle acceleration.