Interstellar detection of O-protonated carbonyl sulfide, HOCS+
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2024
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| author | Sanz-Novo, Miguel Rivilla, Víctor M. Jiménez-Serra, Izaskun Martín-Pintado, Jesús Colzi, Laura Zeng, Shaoshan Megías, Andrés López-Gallifa, Álvaro Martínez-Henares, Antonio Massalkhi, Sarah Tercero, Belén de Vicente, Pablo Andrés, David San Martín, Sergio Requena-Torres, Miguel A. |
| author_facet | Sanz-Novo, Miguel Rivilla, Víctor M. Jiménez-Serra, Izaskun Martín-Pintado, Jesús Colzi, Laura Zeng, Shaoshan Megías, Andrés López-Gallifa, Álvaro Martínez-Henares, Antonio Massalkhi, Sarah Tercero, Belén de Vicente, Pablo Andrés, David San Martín, Sergio Requena-Torres, Miguel A. |
| contents | We present the first detection in space of O-protonated carbonyl sulfide (\ch{HOCS+}), in the midst of an ultradeep molecular line survey toward the G+0.693-0.027 molecular cloud. From the observation of all $K$$_a$ = 0 transitions ranging from $J$$_{lo}$ = 2 to $J$$_{lo}$ = 13 of \ch{HOCS+} covered by our survey, we derive a column density of $N$ = (9 $\pm$ 2)$\times$10$^{12}$ cm$^{-2}$, translating into a fractional abundance relative to H$_2$ of $\sim$7$\times$10$^{-11}$. Conversely, the S-protonated \ch{HSCO+} isomer remains undetected, and we derive an upper limit to its abundance with respect to H$_2$ of $\leq$3$\times$10$^{-11}$, a factor of $\geq$2.3 less abundant than \ch{HOCS+}. We obtain a \ch{HOCS+}/OCS ratio of $\sim$2.5$\times$10$^{-3}$, in good agreement with the prediction of astrochemical models. These models show that one of the main chemical routes to the interstellar formation of \ch{HOCS+} is likely the protonation of OCS, which appears to be more efficient at the oxygen end. Also, we find that high values of cosmic-ray ionisation rates (10$^{-15}$-10$^{-14}$ s$^{-1}$) are needed to reproduce the observed abundance of \ch{HOCS+}. In addition, we compare the O/S ratio across different interstellar environments. G+0.693-0.027 appears as the source with the lowest O/S ratio. We find a \ch{HOCO+}/\ch{HOCS+} ratio of $\sim$31, in accordance with other O/S molecular pairs detected toward this region and also close to the O/S solar value ($\sim$37). This fact indicates that S is not significantly depleted within this cloud due to the action of large-scale shocks, unlike in other sources where S-bearing species remain trapped on icy dust grains. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2402_15405 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Interstellar detection of O-protonated carbonyl sulfide, HOCS+ Sanz-Novo, Miguel Rivilla, Víctor M. Jiménez-Serra, Izaskun Martín-Pintado, Jesús Colzi, Laura Zeng, Shaoshan Megías, Andrés López-Gallifa, Álvaro Martínez-Henares, Antonio Massalkhi, Sarah Tercero, Belén de Vicente, Pablo Andrés, David San Martín, Sergio Requena-Torres, Miguel A. Astrophysics of Galaxies We present the first detection in space of O-protonated carbonyl sulfide (\ch{HOCS+}), in the midst of an ultradeep molecular line survey toward the G+0.693-0.027 molecular cloud. From the observation of all $K$$_a$ = 0 transitions ranging from $J$$_{lo}$ = 2 to $J$$_{lo}$ = 13 of \ch{HOCS+} covered by our survey, we derive a column density of $N$ = (9 $\pm$ 2)$\times$10$^{12}$ cm$^{-2}$, translating into a fractional abundance relative to H$_2$ of $\sim$7$\times$10$^{-11}$. Conversely, the S-protonated \ch{HSCO+} isomer remains undetected, and we derive an upper limit to its abundance with respect to H$_2$ of $\leq$3$\times$10$^{-11}$, a factor of $\geq$2.3 less abundant than \ch{HOCS+}. We obtain a \ch{HOCS+}/OCS ratio of $\sim$2.5$\times$10$^{-3}$, in good agreement with the prediction of astrochemical models. These models show that one of the main chemical routes to the interstellar formation of \ch{HOCS+} is likely the protonation of OCS, which appears to be more efficient at the oxygen end. Also, we find that high values of cosmic-ray ionisation rates (10$^{-15}$-10$^{-14}$ s$^{-1}$) are needed to reproduce the observed abundance of \ch{HOCS+}. In addition, we compare the O/S ratio across different interstellar environments. G+0.693-0.027 appears as the source with the lowest O/S ratio. We find a \ch{HOCO+}/\ch{HOCS+} ratio of $\sim$31, in accordance with other O/S molecular pairs detected toward this region and also close to the O/S solar value ($\sim$37). This fact indicates that S is not significantly depleted within this cloud due to the action of large-scale shocks, unlike in other sources where S-bearing species remain trapped on icy dust grains. |
| title | Interstellar detection of O-protonated carbonyl sulfide, HOCS+ |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2402.15405 |