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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| Online Access: | https://arxiv.org/abs/2605.25467 |
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| _version_ | 1866911715348709376 |
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| author | Sano, H. Fukui, Y. Fujimori, S. Murase, T. Alsaberi, R. Z. E. Filipović, M. D. Rowell, G. Aruga, M. Asano, Y. Bhuvana, R. G. Demachi, F. Einecke, S. Fukaya, N. Hamada, R. Inoue, H. Kamazaki, T. Lazarević, S. Minamidani, T. Smeaton, Z. J. Sudou, H. Tachihara, K. Takaba, H. Tsuge, K. Yamada, R. I. |
| author_facet | Sano, H. Fukui, Y. Fujimori, S. Murase, T. Alsaberi, R. Z. E. Filipović, M. D. Rowell, G. Aruga, M. Asano, Y. Bhuvana, R. G. Demachi, F. Einecke, S. Fukaya, N. Hamada, R. Inoue, H. Kamazaki, T. Lazarević, S. Minamidani, T. Smeaton, Z. J. Sudou, H. Tachihara, K. Takaba, H. Tsuge, K. Yamada, R. I. |
| contents | 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_\mathrm{LSR} \sim$$-32$ km s$^{-1}$ coincide with arc-like structures seen at 8 $μ$m, likely illuminated by strong FUV radiation from Wd1. $^{12}$CO($J$ = 3-2) emission at the same velocity reveals a cavity-like structure with an expansion velocity of $\sim$$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_\mathrm{LSR} \sim$$-55$ and $\sim$$-32$ km s$^{-1}$ clouds, connected by an intermediate-velocity component at $V_\mathrm{LSR} \sim$$-44$ km s$^{-1}$. These characteristics are consistent with signatures of triggered star formation through a cloud-cloud collision and imply that both clouds are physically associated with Wd1. On larger scales, the total interstellar proton column density at $V_\mathrm{LSR}$ $\sim$$-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 $\sim$$1.6 \times 10^6$ $M_\odot$, and the absence of bright synchrotron X-rays, the TeV gamma-ray emission surrounding Wd1 is consistent with the hadronic origin. The present finding allows us to calculate the total energy of accelerated cosmic-ray protons to be $\sim$$6 \times 10^{49}$ erg. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_25467 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Discovery of Molecular and Atomic Gas associated with HESS J1646-458 (Westerlund 1): Spatial TeV Gamma-Ray and Interstellar Proton Correspondence Sano, H. Fukui, Y. Fujimori, S. Murase, T. Alsaberi, R. Z. E. Filipović, M. D. Rowell, G. Aruga, M. Asano, Y. Bhuvana, R. G. Demachi, F. Einecke, S. Fukaya, N. Hamada, R. Inoue, H. Kamazaki, T. Lazarević, S. Minamidani, T. Smeaton, Z. J. Sudou, H. Tachihara, K. Takaba, H. Tsuge, K. Yamada, R. I. High Energy Astrophysical Phenomena Astrophysics of Galaxies 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_\mathrm{LSR} \sim$$-32$ km s$^{-1}$ coincide with arc-like structures seen at 8 $μ$m, likely illuminated by strong FUV radiation from Wd1. $^{12}$CO($J$ = 3-2) emission at the same velocity reveals a cavity-like structure with an expansion velocity of $\sim$$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_\mathrm{LSR} \sim$$-55$ and $\sim$$-32$ km s$^{-1}$ clouds, connected by an intermediate-velocity component at $V_\mathrm{LSR} \sim$$-44$ km s$^{-1}$. These characteristics are consistent with signatures of triggered star formation through a cloud-cloud collision and imply that both clouds are physically associated with Wd1. On larger scales, the total interstellar proton column density at $V_\mathrm{LSR}$ $\sim$$-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 $\sim$$1.6 \times 10^6$ $M_\odot$, and the absence of bright synchrotron X-rays, the TeV gamma-ray emission surrounding Wd1 is consistent with the hadronic origin. The present finding allows us to calculate the total energy of accelerated cosmic-ray protons to be $\sim$$6 \times 10^{49}$ erg. |
| title | Discovery of Molecular and Atomic Gas associated with HESS J1646-458 (Westerlund 1): Spatial TeV Gamma-Ray and Interstellar Proton Correspondence |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2605.25467 |