The mixing of dust and gas in the high latitude translucent cloud MBM 40

TL;DR

This study investigates the dust-to-gas mixing ratio in the high latitude cloud MBM 40 using combined radio and infrared observations, revealing a nearly uniform ratio and a linear correlation between hydrogen column density and dust emission.

Contribution

It introduces two independent methods to estimate molecular and atomic gas column densities and analyze dust-to-gas mixing in a nearby high latitude molecular cloud.

Findings

Dust-to-gas ratio is nearly uniform across MBM 40.

Hydrogen column density correlates linearly with 100 μm dust emission.

The methods effectively combine HI, CO, and infrared data for ISM analysis.

Abstract

Context. High latitude molecular clouds (hereafter HLMCs) permit the study of interstellar gas dynamics and astrochemistry with good accuracy due to their proximity, generally clear lines of sight, and lack of internal star-forming activity which can heavily modify the physical context. MBM 40, one of the nearest HLMCs, has been extensively studied, making it a superb target to infer and study the dust-to-gas mixing ratio (DGMR). Aims. The mixing of dust and gas in the interstellar medium remains a fundamental issue to keep track of astrochemistry evolution and molecular abundances. Accounting for both molecular and atomic gas is difficult because $H_2$ is not directly observable and HI spectra always show different dynamical profiles blended together which are not directly correlated with the cloud. We used two independent strategies to infer the molecular and atomic gas column densities and compute the dust-to-gas mixing ratio. Methods. We combined $HI$ 21 cm and $^{12}CO$ line observations with the IRAS 100 $\mu$m image to infer the dust-to-gas mixing ratio within the cloud. The cloud 21 cm profile was extracted using a hybrid Gaussian decomposition where $^{12}CO$ was used to deduce the total molecular hydrogen column density. Infrared images were used to calculate the dust emission. Results. The dust-to-gas mixing ratio is nearly uniform within the cloud as outlined by the hairpin structure. The total hydrogen column density and 100 $\mu$m emissivity are linearly correlated over a range in $N(H_{tot})$ of one order of magnitude.