# The three-dimensional structure of Galactic molecular cloud complexes out to 2.5 kpc

**Authors:** T. E. Dharmawardena, C. A. L. Bailer-Jones, M. Fouesneau, D. Foreman-Mackey, P. Coronica, T. Colnaghi, T. Müller, J. Henshaw  
**arXiv:** [2210.03615](https://arxiv.org/abs/2210.03615)  
**Date:** 2022-10-07  
**Summary page:** https://www.summarizepaper.com/en/paper/2210.03615v1/

## Key points

- Studying the 3D structure of Galactic molecular clouds is important for understanding physical processes and their impact on star formation
- Gaia mission provides accurate distances to approximately one billion stars, enabling significant progress in this field
- T. E. Dharmawardena et al. present a novel 3D dust mapping algorithm called \texttt{Dustribution} that combines distances obtained from Gaia with extinctions inferred from optical-IR to recover the 3D structure of 16 Galactic molecular cloud complexes at a resolution of approximately one parsec
- Using \texttt{astrodendro}, the authors derive a catalogue of physical parameters for each complex and observe structures with aspect ratios ranging from near-spherical to very elongated shapes
- There is a large variation in cloud environments that is not apparent when studying them in two dimensions
- California and Orion A clouds appear similar on-sky, but California is more sheet-like and massive than Orion A, which could explain their different star-formation rates
- Evidence for dust sputtering in Carina explains its low dust mass measurement
- Defining cloud boundaries in three dimensions is necessary to obtain an accurate mass estimate; simply integrating extinction overestimates masses
- Specific findings about molecular cloud complexes: (i) California is much more massive and extended than Orion A; (ii) Camelopardalis consists of distinct groupings rather than being an interconnected complex; (iii) Chamaeleon appears to be centered on a cavity separating Cha I from Cha II and III; (iv) The Orion A and B molecular clouds lie along the edges of a bubble with a radius of approximately 50 pc centered behind Orion A at a distance of 480 pc; (v) Vela C exhibits a significant distance gradient along the cloud and is the most massive component of the Vela Molecular Ridge.
- Larson's relationship between mass and radius holds true in three dimensions, but characterizing giant molecular clouds uniformly is not easy due to their varied environments especially when adding the third dimension
- T. E. Dharmawardena et al.'s study provides valuable insights into the 3D structure of Galactic molecular clouds and highlights the importance of using accurate distance measurements as well as defining boundaries in three dimensions to obtain reliable physical parameters for these structures.

## Summary

The study of the three-dimensional structure of Galactic molecular clouds is crucial for understanding the impact of physical processes such as turbulence and magnetic fields on these structures and how they affect star formation. With the advent of the Gaia mission, which provides accurate distances to approximately one billion stars, significant progress has been made in this field. In this study, T. E. Dharmawardena et al. present a novel three-dimensional dust mapping algorithm called \texttt{Dustribution} that combines distances obtained from Gaia with extinctions inferred from optical-IR to recover the three-dimensional structure of 16 Galactic molecular cloud complexes at a resolution of approximately one parsec. By using \texttt{astrodendro}, the authors derive a catalogue of physical parameters for each complex and observe structures with aspect ratios ranging from near-spherical to very elongated shapes. They find a large variation in cloud environments that is not apparent when studying them in two dimensions. For example, they show that while California and Orion A clouds appear similar on-sky, California is more sheet-like and massive than Orion A, which could explain their different star-formation rates. The authors also demonstrate evidence for dust sputtering in Carina, their most distant complex, explaining its low dust mass measurement. By calculating the total mass of individual clouds, they demonstrate that defining cloud boundaries in three dimensions is necessary to obtain an accurate mass estimate; simply integrating extinction overestimates masses. Furthermore, T. E. Dharmawardena et al. 's study reveals several interesting findings about specific molecular cloud complexes: (i) California is much more massive and extended than Orion A; (ii) Camelopardalis consists of distinct groupings rather than being an interconnected complex; (iii) Chamaeleon appears to be centred on a cavity separating Cha I from Cha II and III; (iv) The Orion A and B molecular clouds lie along the edges of a bubble with a radius of approximately 50 pc centred behind Orion A at a distance of 480 pc; (v) Vela C exhibits a significant distance gradient along the cloud and is the most massive component of the Vela Molecular Ridge. The authors also demonstrate that it is necessary to define boundaries in three dimensions to accurately determine cloud masses. They show that Larson's relationship between mass and radius holds true in three dimensions whether assuming a spherical shape for the cloud or taking their true extents into account but note that characterising giant molecular clouds uniformly is not an easy task due to their varied environments especially when adding the third dimension. Overall, T. E. Dharmawardena et al. 's study provides valuable insights into the three-dimensional structure of Galactic molecular clouds and highlights the importance of using accurate distance measurements as well as defining boundaries in three dimensions to obtain reliable physical parameters for these structures.