molecules:extragalactic:arh-plus_extragalactic [CDMS classic documentation]

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===== Argonium, ArH+, in Extragalactic Sources =====

H. S. P. Müller, S. Muller, P. Schilke, E. A. Bergin, J. H. Black, M. Gérin, D. C. Lis, D. A. Neufeld, and S. Suri,\\
reported on the\\
**[[https://doi.org/10.1051/0004-6361/201527254|Detection of Extragalactic Argonium, ArH<sup>+</sup>, toward PKS 1830–211]]**\\
//Astron. Astrophys.// **582**, (2015) Art. No. L4.\\
The ground state rotational transitions of <sup>36</sup>ArH<sup>+</sup> and <sup>38</sup>ArH<sup>+</sup> were observed in absorption in the //z// = 0.89 foreground galaxy toward the quasar PKS 1830–211. The Atacama Large Millimeter Array (ALMA) was used in its Early Science Cycle 2 phase. The transitions were redshifted from about 617 GHz to about 327 GHz. The interstellar abundance of <sup>40</sup>Ar is almost negligible, and <sup>40</sup>ArH<sup>+</sup> was accordingly not detected.

The <sup>36</sup>Ar/<sup>38</sup>Ar isotopic ratios were 3.46 ± 0.16 and 4.53 ± 0.33 toward the stronger SW and the weaker NE image, respectively. The values differ from 5.50 ± 0.01 in the Solar neighborhood, suggesting that high-mass supernovae played a greater role in creating elements heavier than helium (metals for astronomers) in the early Universe compared to today, as one would expect; the look-back time at //z// = 0.89 is about 7.5 billion years.\\
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We know from [[molecules:ism:arh-plus|Galactic observations]] that argonium is an excellent tracer of the almost purely atomic and very diffuse interstellar medium.\\
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A. M. Jacob, K. M. Menten, F. Wyrowski, B. Winkel, D. A. Neufeld and B. S. Koribalski<br>
reported on\\
**[[https://doi.org/10.1051/0004-6361/202142544|ArH<sup>+</sup> and H<sub>2</sub>O<sup>+</sup> Absorption towards Luminous Galaxies]]**\\
//Astron. Astrophys.// **659**, (2022) Art. No. 152.\\
The //J// = 1 − 0 transition of <sup>36</sup>ArH<sup>+</sup> was detected with the APEX 12 m dish toward the nearby galaxies NGC 253, NGC 4945, and Arp 220. The molecular fraction of the gas traced by ArH<sup>+</sup> was estimated to be ~10<sup>−3</sup> and that it resides in gas volumes with low electon densities.\\
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Contributor(s): H. S. P. Müller; 10, 2015; 04, 2022

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