Astrochemistry

A Quest For Sulfur-bearing Refractory Species. Identification Of CaS In The Interstellar Medium

By Keith Cowing

Status Report

astro-ph.GA

October 15, 2025

Filed under astro-ph.GA, astrochemistry, astronomy, biochemistry, G351.77-mm1, Interstellar, organic chemistry

A Quest For Sulfur-bearing Refractory Species. Identification Of CaS In The Interstellar Medium — ALMA 1.5 mm continuum emission towards the G351.77−0.54 star-forming region. Crosses mark the positions of the mm continuum sources identified by H. Beuther et al. (2019). The synthesized beam of the image (beam = 0.”21×0.”15, PA= −86◦ ; with an rms ≃ 0.32 mJy beam⁻¹ ) is shown in the bottom-left corner. The spectra shown in Figs. 2 and A1 have been extracted towards the peak position of G351.77-mm1, located at α(J2000) = 17^h26^m42.533^s and δ(J2000) = −36◦ 9′ 17.37″ — astro-ph.GA

The recent detection of refractory molecules in massive star-forming regions provides a means of probing the innermost regions of disks around massive stars. These detections also make it possible to explore the chemical composition of refractories through gas-phase observations.

In this regard, identifying refractory compounds containing sulfur could reveal potential connections between sulfur and refractories, as well as help determine the sulfur budget in these extreme environments.

We find convincing evidence of a reliable detection of CaS, and tentative detections of KS and KSH in the disk G351.77-mm1. These are the first ever identifications of these species in the interstellar medium. The CaS, KS, and KSH column densities are about 3 orders of magnitude lower than those of the abundant sulfur compounds SO₂, CH₃SH and SiS, proving that these species are not the major reservoir of sulfur at the spatial scales probed by our observations.

Higher angular resolution observations at different wavelengths are required to confirm these detections, which are of paramount importance to gain insights into the formation of gas-phase refractory molecules.

A. Tasa-Chaveli, Á. Sánchez-Monge, A. Fuente, A. Ginsburg, H. S. P. Müller, Th. Möller, P. Rivière-Marichalar, D. Navarro-Almaida, G. Esplugues, P. Schilke, M. Rodríguez-Baras, S. Thorwirth, L. Beitia-Antero

Comments: 17 pages, 6 figures, accepted for publication in Astrophysical Journal Letters
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2510.02937 [astro-ph.GA] (or arXiv:2510.02937v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2510.02937
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Submission history
From: Aitana Tasa-Chaveli
[v1] Fri, 3 Oct 2025 12:28:50 UTC (6,358 KB)
https://arxiv.org/abs/2510.02937
Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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