First Images Of Phosphorus Molecules Towards A Proto-Solar Analog


Emission morphologies of Band 4 transitions of PN and PO (colormaps), compared with SiO, CCS, SO2, and 13CH3OH. Contour levels correspond to [4,7,10,13]σ for the 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 continuum peak position is shown with a yellow ‘+’. Restoring beams for PN and PO (purple) and the additional lines (grey/orange) are shown in 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 ALMA Band 3 and 4 observations of PO and PN towards the Class I protostar B1-a, representing the first spatially resolved observations of phosphorus carriers towards a Solar-type star forming region. The phosphorus molecules emit from two distinct clumps, which coincide with regions where the protostellar outflow (traced by SiO) interacts with a filament of dense gas (traced by CCS). Thus, the gas-phase phosphorus seems to originate from the shocking of dense interstellar clumps.

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

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

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

Comments: Accepted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Earth 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
From: Jennifer Bergner
[v1] Mon, 10 Jan 2022 17:11:14 UTC (1,327 KB)
https://arxiv.org/abs/2201.03467
Astrobiology, Astrochemistry

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