X-ray Shadowing Experiments Toward Infrared Dark Clouds

TL;DR

This study uses X-ray shadowing observations of two infrared dark clouds to investigate the distribution of X-ray emitting plasma in the Galaxy, revealing its connection to the interstellar medium and star formation.

Contribution

It demonstrates the effectiveness of X-ray shadowing with XMM-Newton to map the Galactic distribution of X-ray emitting plasma using IRDCs as targets.

Findings

X-ray emission at 3/4 keV is distributed throughout the Galactic disk.

X-ray shadowing confirms the link between X-ray emission and the cooler ISM material.

The results suggest a connection between X-ray plasma and star formation processes.

Abstract

We searched for X-ray shadowing toward two infrared dark clouds (IRDCs) using the MOS detectors on XMM-Newton to learn about the Galactic distribution of X-ray emitting plasma. IRDCs make ideal X-ray shadowing targets of 3/4 kev photons due to their high column densities, relatively large angular sizes, and known kinematic distances. Here we focus on two clouds near 30 deg. Galactic longitude at distances of 2 and 5 kpc from the Sun. We derive the foreground and background column densities of molecular and atomic gas in the direction of the clouds. We find that the 3/4 kev emission must be distributed throughout the Galactic disk. It is therefore linked to the structure of the cooler material of the ISM, and to the birth of stars.