The Musca molecular cloud: The perfect "filament" is still a sheet

TL;DR

This paper presents evidence that the Musca molecular cloud is more accurately described as a sheet-like structure extended along the line of sight, challenging the common filamentary view and providing insights into star formation physics.

Contribution

The study provides a comprehensive analysis combining observations and simulations to demonstrate Musca's sheet-like 3D shape, advancing understanding of molecular cloud geometries.

Findings

Musca is likely a sheet-like structure extended along the line of sight.

Evidence from CO observations and radiative transfer simulations supports a sheet morphology.

The shape influences star formation processes within the cloud.

Abstract

The true 3-dimensional (3D) morphology of the Musca molecular cloud is a topic that has received significant attention lately. Given that Musca does not exhibit intense star-formation activity, unveiling its shape has the potential of also revealing crucial information regarding the physics that dictates the formation of the first generation of stars within molecular clouds. Here, we revisit the shape of Musca and we present a comprehensive array of evidence pointing towards a shape that is extended along the line-of-sight dimension: (a) 3D maps of differential extinction; (b) new non-local thermodynamic equilibrium radiative transfer simulations of CO rotational transitions from a sheet-like, magnetically-dominated simulated cloud; (c) an effective/critical density analysis of available CO observations; (d) indirect consequences that a filamentary structure would have had, from a theoretical star-formation perspective. We conclude that the full collection of observational evidence strongly suggests that Musca has a sheet-like geometry.