Issue |
A&A
Volume 477, Number 1, January I 2008
|
|
---|---|---|
Page(s) | L5 - L8 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20078824 | |
Published online | 20 November 2007 |
Letter to the Editor
Detection of extragalactic H3O
1
SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands e-mail: vdtak@sron.nl
2
Kapteyn Astronomical Institute, University of Groningen, The Netherlands
3
Onsala Space Observatory, Chalmers University of Technology, 43992 Onsala, Sweden
4
Astronomy Department, University of California, 601 Campbell Hall, Berkeley, CA 94720, USA
Received:
10
October
2007
Accepted:
12
November
2007
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.
Key words: galaxies: starburst / galaxies: active / radio lines: galaxies / ISM: molecules
© ESO, 2007
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.