Deep Search For Phosphine In A Prestellar Core

Understanding in which chemical forms phosphorus exists in star- and planet-forming regions and how phosphorus is delivered to planets are of great interest from the viewpoint of the origin of life on Earth. Phosphine (PH₃) is thought to be a key species to understanding phosphorus chemistry, but never has been detected in star- and planet-forming regions.

We performed sensitive observations of the ortho-PH₃ 10−00 transition (266.944 GHz) toward the low-mass prestellar core L1544 with the ACA stand-alone mode of ALMA. The line was not detected down to 3σ levels in 0.07 km s⁻¹ channels of 18 mK. The non-detection provides the upper limit to the gas-phase PH₃ abundance of 5×10⁻¹² with respect to H₂ in the central part of the core.

ALMA 1.2 mm continuum emission toward L1544. The black solid ellipse represents the region where we extract the spectrum and continuum flux discussed in the main text. The synthesized beam size is shown by the gray-filled circle. North is up, and east is to the left. — astro-ph.GA

Based on the gas-ice astrochemical modeling, we find the scaling relationship between the gas-phase PH₃ abundance and the volatile (gas and ice with larger volatility than water) P elemental abundance for given physical conditions.

This characteristic and well-constrained physical properties of L1544 allow us to constrain the upper limit to the volatile P elemental abundance of 5×10⁻⁹, which is a factor of 60 lower than the overall P abundance in the ISM. Then the majority of P should exist in refractory forms.

The volatile P elemental abundance of L1544 is smaller than that in the coma of comet 67P/C-G, implying that the conversion of refractory phosphorus to volatile phosphorus could have occurred along the trail from the presolar core to the protosolar disk through e.g., sputtering by accretion/outflow shocks.

Kenji Furuya, Takashi Shimonishi

Comments: 10 pages, 4 figures, 1 Table, accepted for publication in ApJL
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2406.05978 [astro-ph.GA] (or arXiv:2406.05978v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2406.05978
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Submission history
From: Kenji Furuya
[v1] Mon, 10 Jun 2024 02:34:39 UTC (298 KB)
https://arxiv.org/abs/2406.05978
Astrobiology, Astrochemistry,