Dense gas in normal and active galaxies

Details Dense gas in normal and active galaxies Dense gas in normal and active galaxies

Jan 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008ap%26ss.313..279k&link_type=abstract

Astrophysics and Space Science, Volume 313, Issue 1-3, pp. 279-285

Astronomy and Astrophysics

Astrophysics

11

Ism, Starburst, Seyfert, Abundance

Scientific paper

Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1 0) and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3 2) imaging survey of nearby spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging of Star-forming galaxies), CO(3 2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between the CO(3 2)/CO(1 0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on the other hand, we often find enhanced or overluminous HCN(1 0) emission. The HCN(1 0)/CO(1 0) and HCN(1 0)/HCO+(1 0) intensities are often enhanced up to ˜0.2 0.3 and ˜2 3, respectively. Such elevated ratios have never been observed in the nuclear starburst regions. One possible explanation for these high HCN(1 0)/CO(1 0) and HCN(1 0)/HCO+(1 0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1 0) and the star-formation rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these molecular lines are free from dust extinction.

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