Detection of extragalactic H3O+

F. F. S. van der Tak*, S. Aalto, R. Meijerink

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

38 Citations (Scopus)
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Abstract

Context. The H3O+ molecule probes the oxygen chemistry and the ionization rate of dense circumnuclear gas in galaxies.

Aims. Recent H3O+ observations show variations in the cosmic-ray ionization rate, by factors of >10 within our Galaxy.

Methods. Using the JCMT, we have observed the 364 GHz line of p-H3O+ in the centers of M 82 and Arp 220.

Results. In Arp 220, the line profile suggests that the emission originates in the Western nucleus. In M 82, both the eastern molecular peak and the circumnuclear region contribute to the emission. The derived column densities, abundances, and H3O+/H2O ratios indicate ionization rates similar to or even exceeding that in the Galactic Center.

Conclusions. Model calculations of the chemistry of irradiated molecular gas indicate a likely origin of this high ionization rate in the extended, evolved starburst of M 82. In contrast, irradiation by X-rays from the AGN disk is the most likely model for Arp 220.

Original languageEnglish
Pages (from-to)L5-L8
Number of pages4
JournalAstronomy & Astrophysics
Volume477
Issue number1
DOIs
Publication statusPublished - Jan-2008

Keywords

  • galaxies : starburst
  • galaxies : active
  • radio lines : galaxies
  • ISM : molecules
  • HNC LINE EMISSION
  • DENSE GAS
  • NEARBY GALAXIES
  • ARP 220
  • M82
  • STARBURST
  • SUBMILLIMETER
  • ARP-220
  • WATER
  • DIAGNOSTICS

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