Forming Molecular Hydrogen in a Galaxy Halo Through Star Formation Wind Interactions
Abstract
Molecular hydrogen (H2) is the key ingredient for star formation in galaxies. However, how H2 is distributed in and around galaxies is an open question in astronomy. We report the detection of H2 (covering excitation levels J = 0 to 3) in a unique environment at a distance of 139 kpc from a starbursting luminous infrared galaxy. This is the furthest from a galaxy that H2 has been directly detected to date. This H2 system is unlike any seen before, with a high molecular-to-atomic hydrogen ratio (2%) and an accompanying low neutral hydrogen column density (log10[N(H I)/cm−2] = 18.52+0.13−3.58). Our measurements reveal that the H2 bearing cloud is traveling at ∼100 km s−1 relative to the host galaxy, has a super-solar metallicity, and excites at a single, cold temperature (245+25−21 K) indicating a lack of the ''typical'' core-envelope structure seen in other H2 clouds. Furthermore, our analysis points to the H2 likely being formed through interactions between galactic winds and the gaseous halo surrounding the galaxy. The properties of this cloud suggest that the H2 is short-lived, yet it presents crucial information on the microphysics of the wind-CGM interactions.
Related
- Molecular hydrogen formation on dust: The impact of gas-dust drift on formation efficiency
- The Neutral Hydrogen Gas Content of Star-forming and Quiescent S0 Galaxies
- CHemical Evolution in MassIve star-forming COres (CHEMICO). II. Molecular ions, electron fraction, and cosmic-ray ionisation rate
- What sets the star-formation rate in the Milky Way?. II. Comparing the star-forming clumps from simulations and observations
- Formation of Heavy Seed Black Holes and Little Red Dots-like Compact Clusters in Metal-enriched Star-forming Regions
BibTeX
@misc{koplitz2026forming,
title = {{Forming Molecular Hydrogen in a Galaxy Halo Through Star Formation Wind Interactions}},
author = {Brad Koplitz and Sanchayeeta Borthakur and Timothy Heckman and Frances H. Cashman and Evan Scannapieco and Jason Tumlinson and Hsiao-Wen Chen and Molly Peeples},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.06662},
eprint = {2610.06662},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.06662},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Forming Molecular Hydrogen in a Galaxy Halo Through Star Formation Wind Interactions
AU - Brad Koplitz
AU - Sanchayeeta Borthakur
AU - Timothy Heckman
AU - Frances H. Cashman
AU - Evan Scannapieco
AU - Jason Tumlinson
AU - Hsiao-Wen Chen
AU - Molly Peeples
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2610.06662
UR - https://arxiv.org/abs/2610.06662
AB - Molecular hydrogen (H_2) is the key ingredient for star formation in galaxies. However, how H_2 is distributed in and around galaxies is an open question in astronomy. We report the detection of H_2 (covering excitation levels J = 0 to 3) in a unique environment at a distance of 139 kpc from a starbursting luminous infrared galaxy. This is the furthest from a galaxy that H_2 has been directly detected to date. This H_2 system is unlike any seen before, with a high molecular-to-atomic hydrogen ratio (2%) and an accompanying low neutral hydrogen column density (log_10[N(H I)/cm^−2] = 18.52^+0.13_−3.58). Our measurements reveal that the H_2 bearing cloud is traveling at ∼100 km s^−1 relative to the host galaxy, has a super-solar metallicity, and excites at a single, cold temperature (245^+25_−21 K) indicating a lack of the ''typical'' core-envelope structure seen in other H_2 clouds. Furthermore, our analysis points to the H_2 likely being formed through interactions between galactic winds and the gaseous halo surrounding the galaxy. The properties of this cloud suggest that the H_2 is short-lived, yet it presents crucial information on the microphysics of the wind-CGM interactions.
ER -