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 language | English |
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Pages (from-to) | L5-L8 |
Number of pages | 4 |
Journal | Astronomy & Astrophysics |
Volume | 477 |
Issue number | 1 |
DOIs | |
Publication status | Published - 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