First extragalactic detection of a phosphorus-bearing molecule with ALCHEMI: Phosphorus nitride (PN)
Artikel i vetenskaplig tidskrift, 2022
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) x 10(13) cm(-2) and N = (6.5 +/- 1.6) x 10(12) cm(-2), which translate into abundances with respect to H-2 of chi = (8.0 +/- 1.0) x 10(-12) and chi = (4.4 +/- 1.2) x 10(-12). We derived a low excitation temperature of T-ex = (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.
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) x 10(13) cm(-2) and N = (6.5 +/- 1.6) x 10(12) cm(-2), which translate into abundances with respect to H-2 of chi = (8.0 +/- 1.0) x 10(-12) and chi = (4.4 +/- 1.2) x 10(-12). We derived a low excitation temperature of T-ex = (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.
individual
galaxies
ISM
clouds
abundances
ISM
astrochemistry
NGC 253
molecules
ISM
Författare
D. Haasler
Universidad Rey Juan Carlos
Centro de Astrobiología (INTA-CSIC)
V. M. Rivilla
Istituto nazionale di astrofisica (INAF)
Centro de Astrobiología (INTA-CSIC)
S. Martin
Atacama Large Millimeter-submillimeter Array (ALMA)
European Southern Observatory Santiago
J. Holdship
University College London (UCL)
Universiteit Leiden
S. Viti
University College London (UCL)
Universiteit Leiden
N. Harada
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
Academia Sinica
J. Mangum
National Radio Astronomy Observatory
K. Sakamoto
Academia Sinica
Sebastien Muller
Chalmers, Rymd-, geo- och miljövetenskap, Onsala rymdobservatorium
K. Tanaka
Keio University
Y. Yoshimura
University of Tokyo
K. Nakanishi
National Astronomical Observatory of Japan
The Graduate University for Advanced Studies (SOKENDAI)
L. Colzi
Istituto nazionale di astrofisica (INAF)
Centro de Astrobiología (INTA-CSIC)
L. Hunt
Istituto nazionale di astrofisica (INAF)
K. L. Emig
National Radio Astronomy Observatory
R. Aladro
Max-Planck-Gesellschaft
P. Humire
Max-Planck-Gesellschaft
C. Henkel
King Abdulaziz University
Max-Planck-Gesellschaft
Chinese Academy of Sciences
P. van der Werf
Universiteit Leiden
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 659 A158Ämneskategorier
Astronomi, astrofysik och kosmologi
DOI
10.1051/0004-6361/202142032