CO-to-H_2 Conversion Factor of Molecular Clouds using X-Ray Shadows

TL;DR

This paper introduces a novel method using X-ray shadowing to accurately determine the CO-to-H2 conversion factor in molecular clouds, providing a new tool for studying molecular gas.

Contribution

A new technique leveraging X-ray absorption to measure the CO-to-H2 conversion factor in molecular clouds, validated on specific clouds with archival data.

Findings

Measured $X_{CO}$ for Ophiucus and Corona Australis clouds.

Found $X_{CO} = 1.85 imes 10^{20} ext{H}_2 ext{cm}^{-2}/( ext{K km s}^{-1})$.

Method shows consistency across different X-ray energy bands.

Abstract

A new method to determine the CO-to-H$_2$ conversion factor $X_{\rm CO}$ using absorption of diffuse X-ray emission by local molecular clouds was developed. It was applied to the Ophiucus (G353+17) and Corona Australis (G359-18) clouds using CO-line and soft X-ray archival data. We obtained a value $X_{\rm CO} =1.85 \pm 0.45 \times 10^{20} {\rm H_2 cm^{-2}/(K~ km~ s^{-1})}$ as the average of least-$chi^2$ fitting results for R4 (0.7 keV) and R5 (0.8 keV) bands. Full resolution pdf available at http://www.ioa.s.u-tokyo.ac.jp/~sofue/htdocs/2016Xco/