HCN 3-2 survey towards a sample of local galaxies

Abstract

We present observations of HCN 3-2 emissions towards 37 local galaxies using the 10 m Submillimeter Telescope. HCN 3-2 emission is detected in 23 galaxies. The correlation of infrared luminosity (L_IR) and the luminosity of HCN 3-2 line emission measured in our sample is fitted with a slope of 1.11 and correlation coefficient of 0.91, which follows the linear correlation found in other dense gas tracers in the literature. Although molecular gas above a certain volume density threshold (i.e., $n_{\rm H_2}\ge 10^4\:$ cm^-3) statistically gave a similar relation with infrared luminosity, the large scatter of HCN 3-2/HCN 1-0 ratios for galaxies with different L_IR indicates that dense gas masses estimated from the line luminosities of only one transition of dense gas tracers should be treated with caution for individual galaxies.