Journal Article

Dense molecular gas in nearby gas-rich active galaxiesȪ

Xuejian Jiang, Junzhi Wang and Qiusheng Gu

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 418, issue 3, pages 1753-1763
Published in print December 2011 | ISSN: 0035-8711
Published online December 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19596.x
Dense molecular gas in nearby gas-rich active galaxiesȪ

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We present 3-mm observations obtained with the Institut de Radioastronomie Millimétrique (IRAM) 30-m telescope for 10 nearby gas-rich active galaxies spanning three orders of magnitude in infrared luminosity. Emission lines of HCO+(1–0), HCN(1–0) and C2H(1–0) were simultaneously detected in most galaxies of our sample. We also tentatively detected the rare isotopic species H13CN, HC15N and H13CO+ in up to four galaxies (IC 694, NGC 3690, NGC 4258 and NGC 6240). Our estimation shows that the optical depth of HCN is low to moderate in these galaxies (τ∼ 1–5). After comparing the intensity ratios of different molecular emission lines (HCN/HCO+, C2H/HCN and C2H/HCO+) with the infrared luminosity (LIR), we find that in the infrared luminous sample of five composite (AGN+starburst) galaxies these ratios vary with LIR: the HCN/HCO+ ratio increases with LIR, which is consistent with previous studies, while there is a slight trend in the composite galaxies that both C2H/HCN and C2H/HCO+ ratios decrease with increasing LIR. Although our sample is limited, this trend may possibly imply a relation between the overall gas density and the infrared luminosity of galaxies.

Keywords: ISM: molecules; galaxies: active; galaxies: evolution; galaxies: ISM

Journal Article.  6173 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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