Letter to the Editor

The “C”: The large Chameleon-Musca-Coalsack cloud

¹ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Straße 1, 85748 Garching bei München, Germany
e-mail: edh@mpa-garching.mpg.de
² Ludwig Maximilian University of Munich, Geschwister-Scholl-Platz 1, 80539 München, Germany
³ Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁴ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
⁵ Excellence Cluster ORIGINS, Boltzmannstraße 2, 85748 Garching bei München, Germany

Received: 15 April 2024
Accepted: 7 June 2024

Abstract

Recent advancements in 3D dust mapping have transformed our understanding of the Milky Way’s local interstellar medium, enabling us to explore its structure in three spatial dimensions for the first time. In this Letter, we use the most recent 3D dust map by Edenhofer et al. to study the well-known Chameleon, Musca, and Coalsack cloud complexes, located about 200 pc from the Sun. We find that these three complexes are not isolated but rather connect to form a surprisingly well-defined half-ring, constituting a single C-shaped cloud with a radius of about 50 pc, a thickness of about 45 pc, and a total mass of about 5 × 10⁴ M_⊙, or 9 × 10⁴ M_⊙ if including everything in the vicinity of the C-shaped cloud. Despite the absence of an evident feedback source at its center, the dynamics of young stellar clusters associated with the C structure suggest that a single supernova explosion about 4 Myr–10 Myr ago likely shaped this structure. Our findings support a single origin story for these cloud complexes, suggesting that they were formed by feedback-driven gas compression, and offer new insights into the processes that govern the birth of star-forming clouds in feedback-dominated regions, such as the Scorpius-Centaurus association.