Haasler, D;
Rivilla, VM;
Martin, S;
Holdship, J;
Viti, S;
Harada, N;
Mangum, J;
... van der Werf, P; + view all
(2022)
First extragalactic detection of a phosphorus-bearing molecule with ALCHEMI: Phosphorus nitride (PN).
Astronomy and Astrophysics: a European journal
, 659
, Article A158. 10.1051/0004-6361/202142032.
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Abstract
Context. Phosphorus (P) is a crucial element for life given its central role in several biomolecules. P-bearing molecules have been discovered in different regions of the Milky Way, but not yet towards an extragalactic environment. Aims. We searched for P-bearing molecules outside the Milky Way towards the nearby starburst Galaxy NGC 253. Methods. Using observations from the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) project, we used the MAdrid Data CUBe Analysis package to model the emission of P-bearing molecules assuming local thermodynamic equilibrium (LTE) conditions. We also performed a non-LTE analysis using SpectralRadex. Results. We report the detection of a P-bearing molecule, phosphorus nitride (PN), for the first time in an extragalactic environment, towards two giant molecular clouds (GMCs) of NGC 253. The LTE analysis yields total PN beam-averaged column densities N = (1.20 ± 0.09) - 1013 cm-2 and N = (6.5 ± 1.6) - 1012 cm-2, which translate into abundances with respect to H2 of = (8.0 ± 1.0) - 10-12 and = (4.4 ± 1.2) - 10-12. We derived a low excitation temperature of Tex = (4.4 ± 1.3) K towards the GMC with the brightest PN emission, which indicates that PN is sub-thermally excited. The non-LTE analysis results in column densities consistent with the LTE values. We also searched for other P-bearing molecules (PO, PH3, CP, and CCP), and upper limits were derived. The derived PO/PN ratios are < 1.3 and < 1.7. The abundance ratio between PN and the shock-tracer SiO derived towards NGC 253 follows the same trend previously found towards Galactic sources. Conclusions. Comparison of the observations with chemical models indicates that the derived molecular abundances of PN in NGC 253 can be explained by shock-driven chemistry followed by cosmic-ray-driven photochemistry.
| Type: | Article |
|---|---|
| Title: | First extragalactic detection of a phosphorus-bearing molecule with ALCHEMI: Phosphorus nitride (PN) |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1051/0004-6361/202142032 |
| Publisher version: | http://dx.doi.org/10.1051/0004-6361/202142032 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher's terms and conditions. |
| UCL classification: | UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy UCL > Provost and Vice Provost Offices > UCL BEAMS UCL |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10147606 |
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