Variations between Dust and Gas in the Diffuse Interstellar Medium

Understand

Using the Planck far-infrared and Arecibo GALFA 21-cm line surveys, we identified a set of isolated interstellar clouds (approximately degree-sized on the sky and comprising 100 solar masses) and assessed the ratio of gas mass to dust mass.

• Significant variations of the gas-to-dust ratio are found both from cloud to cloud and within regions of individual clouds; within the clouds, the atomic gas per unit dust decreases by more than a factor of 3 compared to the standard gas-to-dust ratio.
• Three hypotheses are considered.
• First, the apparently low gas-to-dust ratio could be due to molecular gas.