D. Haasler, V. M. Rivilla, S. Martín, J. Holdship, S. Viti, N. Harada, J. Mangum, K. Sakamoto, S. Muller, K. Tanaka, Y. Yoshimura, K. Nakanishi, L. Colzi, L. Hunt, K. L. Emig, R. Aladro, P. Humire, C. Henkel, and P. van der Werf
reported on the
First Extragalactic Detection of a Phosphorus-bearing Molecule with ALCHEMI: Phosphorus Nitride (PN)
Astron. Astrophys. 659, (2022) Art. No. A158.

The J = 2 – 1 and J = 3 – 2 transitions of PN near 93.980 and 140.968 GHz, respectively, were observed with ALMA in the course of a very extensive molecular line survey (84.2 to 373.2 GHz) of the central molecular zone (CMZ) of the near-by star-burst galaxy NGC 253. The molecular cations were only detected toward the SW image representing denser material with a fairly high molecular fraction overall. They were not seen toward the NE image representing less dense material with a lower molecular fraction overall. Formation of SH⁺ thus appears to require higher densities than that best suited for OH⁺ or H₂O⁺.

The ³²S/³⁴S isotopic ratio is 16.2 ± 1.3, lower than the terrestrial ratio of 22, thus suggesting greater importance of supernovae in the elemental synthesis about 7.5 billion years ago compared to today. On the other hand, the ³²S/³⁴S isotopic ratios are still lower, about 10.5, for CS and H₂S in that galaxy, suggesting an even greater importance of higher-mass supernovae in the probably still denser ISM where these two molecules reside.

Contributor(s): H. S. P. Müller; 04, 2022