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Paper: Aperture Synthesis Images of Dense Molecular Gas in Nearby Galaxies with the Nobeyama Millimeter Array
Volume: 217, Imaging at Radio Through Submillimeter Wavelengths
Page: 364
Authors: Kohno, K.; Kawabe, R.; Shibatsuka, T.; Matsushita, S.
Abstract: Aperture synthesis observations of HCN(1 - 0) emission from nearby spiral galaxies has been conducted with the Nobeyama Millimeter Array. Our high resolution (a few arcseconds) data enable us to perform extensive study on the distributions of dense molecular material and its relation to the star formation activity at a few hundred parsecs resolution, which is comparable to the typical size of starburst/star-forming regions in the centers of galaxies. In starburst galaxies, we find a good spatial coincidence between dense molecular gas and star forming regions. The ratios of HCN/CO integrated intensities in brightness temperature scale, RHCN/CO, are enhanced up to 0.1 -- 0.2 in the starburst region, although the ratio quickly drops outside the star forming regions. In contrast, we find a remarkable decrease of the HCN emission in the post-starburst nuclei, despite of strong CO concentrations there. The RHCN/CO values in the central a few hundred pc regions of these quiescent galaxies are very low, 0.02 -- 0.04. A rough correlation between RHCN/CO and Hα/CO ratios, an indicator of star formation efficiency, are found. These results may indicate an intimate link between dense molecular gas and massive star formation, and the fraction of dense molecular gas to the total molecular gas traced with the RHCN/CO may be an important parameter to control the star formation efficiency.
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