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.
