Ammonium hydrosulfide (NH4SH) as a potentially significant sulfur sink in interstellar ices
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arXiv
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| Auteurs principaux: | , , , , , , , , |
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| Format: | Preprint |
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2024
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| _version_ | 1866910791497678848 |
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| author | Slavicinska, Katerina Boogert, Adwin Tychoniec, Łukasz van Dishoeck, Ewine F. van Gelder, Martijn L. Santos, Julia C. Klaassen, Pamela D. Kavanagh, Patrick J. Chuang, Ko-Ju |
| author_facet | Slavicinska, Katerina Boogert, Adwin Tychoniec, Łukasz van Dishoeck, Ewine F. van Gelder, Martijn L. Santos, Julia C. Klaassen, Pamela D. Kavanagh, Patrick J. Chuang, Ko-Ju |
| contents | Sulfur is depleted with respect to its cosmic standard abundance in dense star-forming regions. It has been suggested that this depletion is caused by the freeze-out of sulfur on interstellar dust grains, but the observed abundances and upper limits of sulfur-bearing ices remain too low to account for all of the missing sulfur. Toward the same environments, a strong absorption feature at 6.85 $μ$m is observed, but its long-standing assignment to the NH4+ cation remains tentative. We investigate the plausibility of NH4SH salt serving as a sulfur reservoir and a carrier of the 6.85 $μ$m band in interstellar ices by characterizing its IR signatures and apparent band strengths in water-rich laboratory ice mixtures and using this laboratory data to constrain NH4SH abundances in observations of 4 protostars and 2 cold dense clouds. The observed 6.85 $μ$m feature is fit well with the laboratory NH4SH:H2O ice spectra. NH4+ column densities obtained from the 6.85 $μ$m band range from 8-23% with respect to H2O toward the sample of protostars and dense clouds. The redshift of the 6.85 $μ$m feature correlates with higher abundances of NH4+ with respect to H2O in both the laboratory data presented here and observational data of dense clouds and protostars. The apparent band strength of the SH- feature is likely too low for the feature to be detectable in the spectrally busy 3.9 $μ$m region, but the 5.3 $μ$m NH4+ $ν_{4}$ + SH- R combination mode may be an alternative means of detection. Its tentative assignment adds to mounting evidence supporting the presence of NH4+ salts in ices and is the first tentative observation of the SH- anion toward interstellar ices. If the majority ($\gtrsim$80-85%) of the NH4+ cations quantified toward the investigated sources in this work are bound to SH- anions, then NH4SH salts could account for up to 17-18% of their sulfur budgets. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2410_02860 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Ammonium hydrosulfide (NH4SH) as a potentially significant sulfur sink in interstellar ices Slavicinska, Katerina Boogert, Adwin Tychoniec, Łukasz van Dishoeck, Ewine F. van Gelder, Martijn L. Santos, Julia C. Klaassen, Pamela D. Kavanagh, Patrick J. Chuang, Ko-Ju Astrophysics of Galaxies Solar and Stellar Astrophysics Sulfur is depleted with respect to its cosmic standard abundance in dense star-forming regions. It has been suggested that this depletion is caused by the freeze-out of sulfur on interstellar dust grains, but the observed abundances and upper limits of sulfur-bearing ices remain too low to account for all of the missing sulfur. Toward the same environments, a strong absorption feature at 6.85 $μ$m is observed, but its long-standing assignment to the NH4+ cation remains tentative. We investigate the plausibility of NH4SH salt serving as a sulfur reservoir and a carrier of the 6.85 $μ$m band in interstellar ices by characterizing its IR signatures and apparent band strengths in water-rich laboratory ice mixtures and using this laboratory data to constrain NH4SH abundances in observations of 4 protostars and 2 cold dense clouds. The observed 6.85 $μ$m feature is fit well with the laboratory NH4SH:H2O ice spectra. NH4+ column densities obtained from the 6.85 $μ$m band range from 8-23% with respect to H2O toward the sample of protostars and dense clouds. The redshift of the 6.85 $μ$m feature correlates with higher abundances of NH4+ with respect to H2O in both the laboratory data presented here and observational data of dense clouds and protostars. The apparent band strength of the SH- feature is likely too low for the feature to be detectable in the spectrally busy 3.9 $μ$m region, but the 5.3 $μ$m NH4+ $ν_{4}$ + SH- R combination mode may be an alternative means of detection. Its tentative assignment adds to mounting evidence supporting the presence of NH4+ salts in ices and is the first tentative observation of the SH- anion toward interstellar ices. If the majority ($\gtrsim$80-85%) of the NH4+ cations quantified toward the investigated sources in this work are bound to SH- anions, then NH4SH salts could account for up to 17-18% of their sulfur budgets. |
| title | Ammonium hydrosulfide (NH4SH) as a potentially significant sulfur sink in interstellar ices |
| topic | Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2410.02860 |