Discovery of Molecular and Atomic Gas associated with HESS J1646-458 (Westerlund 1): Spatial TeV Gamma-Ray and Interstellar Proton Correspondence
Abstract
We report CO and HI studies of molecular and atomic gas toward the TeV gamma-ray source HESS J1646−458, widely considered to be associated with the young massive cluster Westerlund 1 (Wd1). We found that molecular clouds at VLSR ∼−32 km s−1 coincide with arc-like structures seen at 8 μm, likely illuminated by strong FUV radiation from Wd1. 12CO(J = 3-2) emission at the same velocity reveals a cavity-like structure with an expansion velocity of ∼$5$ km s−1 toward the central region of Wd1, suggesting a recently formed wind-blown bubble driven by the cluster. We also identify a complementary spatial distribution between the VLSR ∼−55 and ∼−32 km s−1 clouds, connected by an intermediate-velocity component at VLSR ∼−44 km s−1. These characteristics are consistent with signatures of triggered star formation through a cloud-cloud collision and imply that both clouds are physically associated with Wd1. On larger scales, the total interstellar proton column density at VLSR ∼−36-−23 km s−1 shows a moderate spatial correspondence with the TeV gamma-ray shell. Together with this correlation, a substantial gas mass of ∼1.6 × 106 M⊙, and the absence of bright synchrotron X-rays, the TeV gamma-ray emission surrounding Wd1 is consistent with the hadronic origin. The present finding allows us to calculate the total energy of accelerated cosmic-ray protons to be ∼6 × 1049 erg.
Versions
Related
- The Central Molecular Zone of our Galaxy, a chemical complexity factory: first interstellar detections of molecules towards G+0.693
- Magnetized Interstellar Molecular Clouds. III. Filament Collisions and Core Formation: Insights into Substructures and Evolution
- Magnetized interstellar molecular clouds - III. Filament Collisions and Core Formation: Insights into Substructures and Evolution
- Interstellar Complex Organic Molecules and Molecular Outflows in NGC 1333 IRAS 4B and 4B' Observed Using NOEMA
- Silicate cosmic dust grain collisions in the interstellar medium: A molecular dynamics study
BibTeX
@misc{sano2026discovery,
title = {{Discovery of Molecular and Atomic Gas associated with HESS J1646-458 (Westerlund 1): Spatial TeV Gamma-Ray and Interstellar Proton Correspondence}},
author = {H. Sano and Y. Fukui and S. Fujimori and T. Murase and R. Z. E. Alsaberi and M. D. Filipović and G. Rowell and M. Aruga and Y. Asano and R. G. Bhuvana and F. Demachi and S. Einecke and N. Fukaya and R. Hamada and H. Inoue and T. Kamazaki and S. Lazarević and T. Minamidani and Z. J. Smeaton and H. Sudou and K. Tachihara and H. Takaba and K. Tsuge and R. I. Yamada},
howpublished = {arXiv},
year = {2026},
month = may,
doi = {10.48550/arxiv.2605.25467},
eprint = {2605.25467},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.25467},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Discovery of Molecular and Atomic Gas associated with HESS J1646-458 (Westerlund 1): Spatial TeV Gamma-Ray and Interstellar Proton Correspondence
AU - H. Sano
AU - Y. Fukui
AU - S. Fujimori
AU - T. Murase
AU - R. Z. E. Alsaberi
AU - M. D. Filipović
AU - G. Rowell
AU - M. Aruga
AU - Y. Asano
AU - R. G. Bhuvana
AU - F. Demachi
AU - S. Einecke
AU - N. Fukaya
AU - R. Hamada
AU - H. Inoue
AU - T. Kamazaki
AU - S. Lazarević
AU - T. Minamidani
AU - Z. J. Smeaton
AU - H. Sudou
AU - K. Tachihara
AU - H. Takaba
AU - K. Tsuge
AU - R. I. Yamada
PY - 2026
DA - 2026/05/25
PB - arXiv
DO - 10.48550/arxiv.2605.25467
UR - https://arxiv.org/abs/2605.25467
AB - We report CO and HI studies of molecular and atomic gas toward the TeV gamma-ray source HESS J1646−458, widely considered to be associated with the young massive cluster Westerlund 1 (Wd1). We found that molecular clouds at V_LSR ∼−32 km s^−1 coincide with arc-like structures seen at 8 μm, likely illuminated by strong FUV radiation from Wd1. ^12CO(J = 3-2) emission at the same velocity reveals a cavity-like structure with an expansion velocity of ∼$5$ km s^−1 toward the central region of Wd1, suggesting a recently formed wind-blown bubble driven by the cluster. We also identify a complementary spatial distribution between the V_LSR ∼−55 and ∼−32 km s^−1 clouds, connected by an intermediate-velocity component at V_LSR ∼−44 km s^−1. These characteristics are consistent with signatures of triggered star formation through a cloud-cloud collision and imply that both clouds are physically associated with Wd1. On larger scales, the total interstellar proton column density at V_LSR ∼−36-−23 km s^−1 shows a moderate spatial correspondence with the TeV gamma-ray shell. Together with this correlation, a substantial gas mass of ∼1.6 × 10^6 M_⊙, and the absence of bright synchrotron X-rays, the TeV gamma-ray emission surrounding Wd1 is consistent with the hadronic origin. The present finding allows us to calculate the total energy of accelerated cosmic-ray protons to be ∼6 × 10^49 erg.
ER -