First images of phosphorus molecules towards a proto-solar analogue

Emission morphologies of band 4 transitions of PN and PO (color maps), compared to SiO, CCS, SO2 and 13CH3OH. The contour levels correspond to [4,7,10,13]σ for line data, where σ is 54, 56, 1.7, 3.6 and 3.2 mJy beam−1 km s −1 for SiO 2–1, SiO 6–5, CCS, SO2 and 13CH3OH, respectively. The position of the continuum peak is indicated by a yellow ‘+’. Restoration beams for PN and PO (purple) and additional lines (gray/orange) are displayed at the bottom right of each panel.

The chemistry of phosphorus in star and planet forming regions is poorly understood, despite the central role of phosphorus in terrestrial biochemistry.

We present the ALMA Band 3 and 4 observations of PO and PN toward the class I protostar B1-a, representing the first spatially resolved observations of phosphorus carriers toward a solar-like star-forming region. The phosphorus molecules emit from two distinct clusters, which coincide with regions where protostellar flow (traced by SiO) interacts with a dense gas filament (traced by CCS). Thus, gas-phase phosphorus appears to come from the collision of dense interstellar clusters.

Based on observed emission patterns, PO and PN appear to be daughter products of a solid phosphorus support with volatility intermediate between ices and silicate grains. Interstellar shocks may therefore play an important role in the conversion of semi-refractory phosphorus into a more volatile form before its incorporation into cometary ices.

Indeed, the (PO+PN)/CH3OH ratio is similar in B1-a and comet 67P, implying a comparable pool of volatile phosphorus. The PO/PN ratio ranges from ~1 to 8 on B1-a. The northern emission block exhibits a lower PO/PN ratio and lower 13CH3OH emission than the southern block, indicating distinct shock physics and chemistry at the two positions. Resolute observations of P carriers to additional sources are needed to better understand what regulates these PO/PN ratio variations in protostellar environments.

Jennifer B. Bergner, Andrew M. Burkhardt, Karin I. Oberg, Thomas S. Rice, Edwin A. Bergin

Comments: Accepted at ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Terrestrial and planetary astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2201.03467 [astro-ph.GA] (or arXiv:2201.03467v1 [astro-ph.GA] for this version)
Submission history
By: Jennifer Bergner
[v1] Mon Jan 10 2022 5:11:14 PM UTC (1327 KB)
Astrobiology, Astrochemistry

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