1. Purple Mountain Obs. CAS CHINA 2005 LiJiang International Starburst Workshop The Dense Molecular Connection Between IR and RC Emission In Galaxies Fan Liu & Yu Gao (Purple Mountain Obs. CAS CHINA)

2. Purple Mountain Obs. CAS CHINA 2005 LiJiang International Starburst Workshop The Sample is drawn from Gao & Solomon ’ s HCN survey (2004) which include 65 galaxies. HCN, IR and CO luminosities are gained from Gao & Solomon ’ s paper(2004). The radio continuum (RC) flux is mainly gained from NVSS.

3. Purple Mountain Obs. CAS CHINA 2005 LiJiang International Starburst Workshop Figure 1 shows a very tight correlation between RC and HCN luminosity with a correlation coefficient R= 0.90. Compare with the correlation between IR and HCN (R= 0.94), the difference is not that significant. Figure 2 shows the correlation between ratio RC/CO (SFE) and ratio HCN/CO (dense molecular gas fraction). The correlation coefficient is 0.62.

4. Purple Mountain Obs. CAS CHINA 2005 LiJiang International Starburst Workshop Some correlations between the ratios of the 4 quantities, RC, IR, HCN and CO, e.g. : suggest that only RC&IR and HCN&IR have truly physical relations.CorrelationRR^2 IR/HCN vs. RC/HCN IR/CO vs. RC/CO 0.740.840.550.72 IR/RC vs. CO/RC IR/RC vs. HCN/RC 0.550.700.310.49 RC/IR vs. CO/IR RC/IR vs. HCN/IR -0.03-0.050.00090.0022 The same conclusion is also summarized by the 3-parameter fits: Log RC(HCN; IR) =  0.002log HCN + 1.05 log IR + 5.59 Log IR(HCN; RC) = 0.43 log HCN + 0.54 log RC + 4.35 Log HCN( IR; RC) = 0.002 log RC + 0.90 log IR + 1.89.

5. Purple Mountain Obs. CAS CHINA 2005 LiJiang International Starburst Workshop The Combination of the two tight correlations, IR — RC correlation and IR — HCN correlation, results in the tight correlation between RC and HCN, which confirms us the practicability of using RC luminosity instead of IR luminosity as an indicator of star formation rate (SFR). The far better high resolution capability of radio observatories than IR observatories allow us to study SFR of more distant galaxies and detailed SF region in nearby galaxies.

6. Purple Mountain Obs. CAS CHINA 2005 LiJiang International Starburst Workshop Thanks!