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A Nearby Dark Molecular Cloud in the Local Bubble Revealed via H2 Fluorescence
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A Nearby Dark Molecular Cloud in the Local Bubble Revealed via H2 Fluorescence

Blakesley Burkhart, Thavisha E Dharmawardena, Shmuel Bialy, Thomas J Haworth, Fernando Cruz Aguirre, Young-Soo Jo, B-G Andersson, Haeun Chung, Jerry Edelstein, Isabelle Grenier, …
ArXiV.org
Cornell University
04/24/2025
DOI: 10.48550/arxiv.2504.17843
url
https://doi.org/10.48550/arxiv.2504.17843View
Preprint (Author's original)This preprint has not been evaluated by subject experts through peer review. Preprints may undergo extensive changes and/or become peer-reviewed journal articles. Open Access

Abstract

A longstanding prediction in interstellar theory posits that significant quantities of molecular gas, crucial for star formation, may be undetected due to being ``dark" in commonly used molecular gas tracers, such as carbon monoxide. We report the discovery of Eos, the closest dark molecular cloud, located just 94 parsecs from the Sun. This cloud is the first molecular cloud ever to be identified using H_2 far ultra-violet (FUV) fluorescent line emission, which traces molecular gas at the boundary layers of star-forming and supernova remnant regions. The cloud edge is outlined along the high-latitude side of the North Polar Spur, a prominent x-ray/radio structure. Our distance estimate utilizes 3D dust maps, the absorption of the soft X-ray background, and hot gas tracers such as O\,{\sc vi}; these place the cloud at a distance consistent with the Local Bubble's surface. Using high-latitude CO maps we note a small amount (M_{\rm{H}_2}\approx20-40\,M_\odot) of CO-bright cold molecular gas, in contrast with the much larger estimate of the cloud's true molecular mass (M_{\rm{H}_2}\approx3.4\times 10^3\,M_\odot), indicating most of the cloud is CO-dark. Combining observational data with novel analytical models and simulations, we predict this cloud will photoevaporate in 5.7 million years, placing key constraints on the role of stellar feedback in shaping the closest star-forming regions to the Sun.
Physics - Astrophysics of Galaxies

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