HCN 3-2 survey towards a sample of local galaxies

We present observations of HCN 3-2 emissions towards 37 local galaxies using 10-m Submillimeter Telescope (SMT). HCN 3-2 emission is detected in 23 galaxies. The correlation of infrared luminosity (LIR) 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 literatures. Although molecular gas above a certain volume density threshold (i.e., $n_{\rm H_2}\geq$ 10$^4$ cm$^{-3}$) statistically gave similar relation with infrared luminosity, the large scatter of HCN 3-2/HCN1-0 ratios for galaxies with different LIR 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.