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Date and Time of the Query: 2019-06-16 T23:33:01 PDT
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For refcode 2004ApJS..152...63G:
Retrieve 53 NED objects in this reference.
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NED Abstract

Copyright by American Astronomical Society. Reproduced by permission
2004ApJS..152...63G HCN Survey of Normal Spiral, Infrared-luminous, and Ultraluminous Galaxies Yu Gao and Philip M. Solomon Abstract. We report systematic HCN J = 1-0 (and CO) observations of a sample of 53 infrared (IR) and/or CO-bright and/or luminous galaxies, including seven ultraluminous infrared galaxies, nearly 20 luminous infrared galaxies, and more than a dozen of the nearest normal spiral galaxies. This is the largest and most sensitive HCN survey of galaxies to date. All galaxies observed so far follow the tight correlation between the IR luminosity L_IR_ and the HCN luminosity L_HCN_ initially proposed by Solomon, Downes, & Radford, which is detailed in a companion paper. We also address here the issue of HCN excitation. There is no particularly strong correlation between L_HCN_ and the 12 microns luminosity; in fact, of all the four IRAS bands, the 12 microns luminosity has the weakest correlation with the HCN luminosity. There is also no evidence of stronger HCN emission or a higher ratio of HCN and CO luminosities L_HCN_/L_CO_ for galaxies with excess 12 microns emission. This result implies that mid-IR radiative pumping, or populating, of the J=1 level of HCN by a mid-IR vibrational transition is not important compared with the collisional excitation by dense molecular hydrogen. Furthermore, large velocity gradient calculations justify the use of HCN J = 1-0 emission as a tracer of high-density molecular gas (>~3x10^4^/{tau}cm^-3^) and give an estimate of the mass of dense molecular gas from HCN observations. Therefore, L_HCN_ may be used as a measure of the total mass of dense molecular gas, and the luminosity ratio L_HCN_/L_CO_ may indicate the fraction of molecular gas that is dense. Keywords: Galaxies: ISM, Galaxies: Starburst, Infrared: Galaxies, ISM: Molecules, Radio Lines: Galaxies, Surveys
Retrieve 53 NED objects in this reference.
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