1999/09/24 by Kotaro Kohno, Kohno, Kotaro, Ryohei Kawabe +6
Chemistry · Engineering · Physics and Astronomy · #Advanced Thermodynamic Systems and Engines #Astrophysics (astro-ph) #Astrophysics and Star Formation Studies #FOS: Physical sciences #Spectroscopy and Laser Applications #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9909422
2 pages, 1 figure, to appear in the proceedings of ``Imaging at Radio through Submillimeter Wavelengths'', held at Tucson, AZ, June 6-9, 1999, ed. J. Mangum (ASP: San Francisco)
arxiv created 1999/09/24 · openalex publication_date 1999/09/24 · arxiv updated 2009/12/01 · openalex created_date 2021/01/05 · openalex updated_date 2026/07/28
In order to study the distribution of dense molecular gas and its relation to\nthe central activities (starburst and AGN) in galaxies, we have conducted an\nimaging survey of HCN(1-0) and HCO+(1-0) emissions from nearby spiral galaxies\nwith the Nobeyama Millimeter Array. In starburst galaxies, we find that there\nis good spatial coincidence between dense molecular gas and star-forming\nregions. The ratios of HCN to CO integrated intensities on the brightness\ntemperature scale, R(HCN/CO), are as high as 0.1 to 0.2 in the starburst\nregions, and quickly decrease outside of these regions. In contrast, we find a\nremarkable decrease of the HCN emission in the post-starburst nuclei, despite\nthe strong CO concentrations there. The R(HCN/CO) values in the central a few\n100 pc regions of these quiescent galaxies are very low, 0.02 to 0.04. A rough\ncorrelation between R(HCN/CO) and Ha/CO ratios, which is an indicator of star\nformation efficiency, is found at a few 100 pc scale. The fraction of dense\nmolecular gas in the total molecular gas, measured from R(HCN/CO), may be an\nimportant parameter that controls star formation. In some Seyfert galaxies we\nfind extremely high R(HCN/CO) exceeding 0.3. These very high ratios are never\nobserved even in strong starburst regions, implying a physical link between\nextremely high R(HCN/CO) and Seyfert activity.\n