First images of phosphorus molecules towards a proto-Solar analog

TL;DR

This study presents the first spatially resolved images of phosphorus molecules PO and PN in a Solar-type star forming region, revealing shock-related chemistry and potential links to cometary phosphorus reservoirs.

Contribution

It provides the first detailed spatial observations of phosphorus carriers in a protostar, highlighting shock processes affecting phosphorus chemistry in star formation.

Findings

Phosphorus molecules are emitted from shock-interacting dense gas regions.

PO and PN likely originate from solid phosphorus carriers affected by shocks.

The observed phosphorus ratios are comparable to those in comet 67P.

Abstract

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.