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| Main Authors: | , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2505.22117 |
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| _version_ | 1866912400026894336 |
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| author | Fuente, Asunción Esplugues, Gisela Rivière-Marichalar, Pablo Navarro-Almaida, David Martín-Doménech, Rafael Muñoz-Caro, Guillermo M. Sánchez-Monge, Álvaro Taillard, Angèle Carrascosa, Héctor Miranzo-Pastor, Julián J. Tasa-Chaveli, Aitana Fernández-Ruiz, Patricia Guzmán, Viviana V. Goicoechea, Javier R. Gerin, Maryvonne Pety, Jerome |
| author_facet | Fuente, Asunción Esplugues, Gisela Rivière-Marichalar, Pablo Navarro-Almaida, David Martín-Doménech, Rafael Muñoz-Caro, Guillermo M. Sánchez-Monge, Álvaro Taillard, Angèle Carrascosa, Héctor Miranzo-Pastor, Julián J. Tasa-Chaveli, Aitana Fernández-Ruiz, Patricia Guzmán, Viviana V. Goicoechea, Javier R. Gerin, Maryvonne Pety, Jerome |
| contents | Sulfur is essential for life, but its abundance and distribution in the interstellar medium remain uncertain, with over 90% of sulfur undetected in cold molecular clouds. Sulfur allotropes (S$_{\rm n}$) have been proposed as possible reservoirs, but the only detected interstellar molecule with a disulfide bond is S$_2$H in the Horsehead Nebula, making the estimation of sulfur chains abundances difficult. Here we present total-power ALMA images of H$_2$S, S$_2$H, SO$_2$, CO$^+$, and SH$^+$ towards the Horsehead nebula. These observations, with unprecedented sensitivity (rms $\sim$ 1.5 mK), provide the first detections of SH$^+$ and CO$^+$ in this region, together with the identification of a new S$_2$H line. The comparison of the spectroscopic images of H$_2$S, S$_2$H, SO$_2$, CO$^+$ and SH$^+$ shows that the S$_2$H emission originates from a warm gas layer adjacent to the photodissociation front. The emission peak of S$_2$H is offset from those of reactive ions such as SH$^+$, CO$^+$, and SO$^+$, suggesting that gas-phase reactions involving SH$^+$ and H$_2$S are not the dominant formation pathway of S$_2$H. Instead, we propose that S$_2$H is desorbed from irradiated grain surfaces by non-thermal processes. The SH$^+$ detection indicates that sulfur is not significantly depleted at the UV-irradiated edge of the molecular cloud, arguing against a major refractory sulfur reservoir in the interior of molecular clouds. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_22117 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The sulfur plume in the Horsehead nebula: New detections of S$_2$H, SH$^+$, and CO$^+$ Fuente, Asunción Esplugues, Gisela Rivière-Marichalar, Pablo Navarro-Almaida, David Martín-Doménech, Rafael Muñoz-Caro, Guillermo M. Sánchez-Monge, Álvaro Taillard, Angèle Carrascosa, Héctor Miranzo-Pastor, Julián J. Tasa-Chaveli, Aitana Fernández-Ruiz, Patricia Guzmán, Viviana V. Goicoechea, Javier R. Gerin, Maryvonne Pety, Jerome Astrophysics of Galaxies Sulfur is essential for life, but its abundance and distribution in the interstellar medium remain uncertain, with over 90% of sulfur undetected in cold molecular clouds. Sulfur allotropes (S$_{\rm n}$) have been proposed as possible reservoirs, but the only detected interstellar molecule with a disulfide bond is S$_2$H in the Horsehead Nebula, making the estimation of sulfur chains abundances difficult. Here we present total-power ALMA images of H$_2$S, S$_2$H, SO$_2$, CO$^+$, and SH$^+$ towards the Horsehead nebula. These observations, with unprecedented sensitivity (rms $\sim$ 1.5 mK), provide the first detections of SH$^+$ and CO$^+$ in this region, together with the identification of a new S$_2$H line. The comparison of the spectroscopic images of H$_2$S, S$_2$H, SO$_2$, CO$^+$ and SH$^+$ shows that the S$_2$H emission originates from a warm gas layer adjacent to the photodissociation front. The emission peak of S$_2$H is offset from those of reactive ions such as SH$^+$, CO$^+$, and SO$^+$, suggesting that gas-phase reactions involving SH$^+$ and H$_2$S are not the dominant formation pathway of S$_2$H. Instead, we propose that S$_2$H is desorbed from irradiated grain surfaces by non-thermal processes. The SH$^+$ detection indicates that sulfur is not significantly depleted at the UV-irradiated edge of the molecular cloud, arguing against a major refractory sulfur reservoir in the interior of molecular clouds. |
| title | The sulfur plume in the Horsehead nebula: New detections of S$_2$H, SH$^+$, and CO$^+$ |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2505.22117 |