We present observations made with the 10 m Heinrich Hertz Submillimeter Telescope of HCN(3-2) emission from a sample of 30 nearby galaxies ranging in infrared luminosity from 10 10 to 10 12.5 L ☉ and HCN(3-2) luminosity from 10 6 to 10 9 K km s −1 pc 2 . We examine the correlation between the infrared luminosity and HCN(3-2) luminosity and find that the best-fit linear regression has a slope (in log-log space) of 0.74 ± 0.12. Including recently published data from Graciá-Carpio et al. tightens the constraints on the best-fit slope to 0.79 ± 0.09. This slope below unity suggests that the HCN(3-2) molecular line luminosity is not linearly tracing the amount of dense gas. Our results are consistent with predictions from recent theoretical models that find slopes below unity when the line luminosity depends on the average gas density with a power-law index greater than a Kennicutt-Schmidt index of 1.5.
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Bussmann et al. (2008) studied this question.
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