The First Steps of Interstellar Phosphorus Chemistry

Phosphorus-bearing species are an essential key to form life on Earth, however they have barely been detected in the interstellar medium. Since only PN and PO have been identified so far towards star-forming regions, the chemical formation pathways of P-bearing molecules are not easy to constrain and are thus highly debatable.

An important factor still missing in the chemical models is the initial elemental abundance of phosphorus, i.e. the depletion level of P. In order to overcome this problem, we study P-bearing species in diffuse/translucent clouds. In these objects phosphorus is mainly in the gas phase and therefore the elemental initial abundance needed in our chemical simulations corresponds to the cosmic one and is thus well constrained. An advanced chemical model with an updated P-chemistry network has been used. Single-pointing observations were performed with the IRAM 30m telescope towards the line of sight to the blazar B0355+508 aiming for the (2-1) transitions of PN, PO, HCP and CP. This line of sight incorporates five diffuse/translucent clouds. The (2-1) transitions of the PN, PO, HCP and CP were not detected.

We report detections of the (1-0) lines of 13CO, HNC and CN along with a first detection of C34S. We have reproduced the observations of HNC, CN, CS and CO in every cloud by applying typical conditions for diffuse/translucent clouds. According to our best-fit model, the most abundant P-bearing species are HCP and CP (∼10−10), followed by PN, PO and PH3 (∼10−11). We show that the production of P-bearing species is favoured towards translucent rather than diffuse clouds, where the environment provides a stronger shielding from the interstellar radiation. Based on our improved model, the (1-0) transitions of HCP, CP, PN and PO are expected to be detectable with estimated intensities up to ∼200 mK.

Johanna Chantzos, Victor M. Rivilla, Anton Vasyunin, Elena Redaelli, Luca Bizzocchi, Francesco Fontani, Paola Caselli
(Submitted on 29 Oct 2019)

Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1910.13449 [astro-ph.GA] (or arXiv:1910.13449v1 [astro-ph.GA] for this version)
Submission history
From: Johanna Chantzos
[v1] Tue, 29 Oct 2019 16:20:00 UTC (646 KB)
https://arxiv.org/abs/1910.13449
Astrobiology, Astrochemistry