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H3O+ line emission ...
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Aalto, Susanne,1964Chalmers tekniska högskola,Chalmers University of Technology
(author)
H3O+ line emission from starbursts and AGNs
- Article/chapterEnglish2011
Publisher, publication year, extent ...
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2011-01-26
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EDP Sciences,2011
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electronicrdacarrier
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LIBRIS-ID:oai:research.chalmers.se:f1561749-628a-4493-9985-05e1a81896c5
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https://research.chalmers.se/publication/139052URI
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https://research.chalmers.se/publication/509621URI
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https://doi.org/10.1051/0004-6361/201015878DOI
Supplementary language notes
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Language:English
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Summary in:English
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Subject category:art swepub-publicationtype
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Subject category:ref swepub-contenttype
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Context. The H3O+ molecule probes the chemistry and the ionization rate of dense circumnuclear gas in galaxies. Aims. We use the H3O+ molecule to investigate the impact of starburst and AGN activity on the chemistry of the molecular interstellar medium. Methods. Using the JCMT, we have observed the 3(2)(+)-2(2)(-) 364 GHz line of p-H3O+ towards the centres of seven active galaxies. Results. We have detected p-H3O+ towards IC 342, NGC 253, NGC 1068, NGC 4418, and NGC 6240. Upper limits were obtained for IRAS 15250 and Arp 299. We find large H3O+ abundances (N(H3O+)/N(H-2) greater than or similar to 10(-8)) in all detected galaxies apart from in IC 342 where it is about one order of magnitude lower. We note, however, that uncertainties in N(H3O+) may be significant due to lack of definite information on source size and excitation. We furthermore compare the derived N(H3O+) with N(HCO+) and find that the H3O+ to HCO+ column density ratio is large in NGC 1068 ( 24), moderate in NGC 4418 and NGC 253 ( 4-5), slightly less than unity in NGC 6240 ( 0.7) and lowest in IC 342 ( 0.2-0.6). We compare our results with models of X-ray and photon dominated regions ( XDRs and PDRs). Conclusions. For IC 342 we find that a starburst PDR chemistry can explain the observed H3O+ abundance. For the other galaxies, the large H3O+ columns are generally consistent with XDR models. In particular for NGC 1068 the elevated N(H3O+)/N(HCO+) ratio suggests a low column density XDR. For NGC 4418 however, large HC3N abundances are inconsistent with the XDR interpretation. An alternative possibility is that H3O+ forms through H2O evaporating off dust grains and reacting with HCO+ in warm, dense gas. This scenario could also potentially fit the results for NGC 253. Further studies of the excitation and distribution of H3O+-aswell as Herschel observations of water abundances - will help to further constrain the models.
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Costagliola, Francesco,1981Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)costagli
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van der Tak, F. F. S.Rijksuniversiteit Groningen,University of Groningen
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Meijerink, R.Universiteit Leiden (UL),Leiden University (UL)
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Chalmers tekniska högskolaRijksuniversiteit Groningen
(creator_code:org_t)
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In:Astronomy and Astrophysics: EDP Sciences527:80004-63611432-0746
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