Zhi-Yu Zhang (ESO) ---- Dense gas tracers and star formation laws: Multi-transition CS survey in nearby active star-forming galaxies

Recent studies on star formation indicate that stars, especially the massive stars, are predominantly formed in dense molecular cores. I will present a survey of multiple transitions of CS (from J=1-0 to 7-6), and HCN/HCO+ J=4-3 in nearby star-forming galaxies, including normal spirals, starburst, and ULIRGs. We find linear correlations between the luminosities of L_IR and L'_gas for all dense gas tracers across eight magnitudes of IR luminosity (L_IR from 10^4 Lsun to 10^12 L_sun), on scales from entire galaxies to Galactic dense cores. Irrespective of the critical density of a specific transition, dense molecular gas is universally related in a linear way to star forming activities for self-gravitationally bound gas systems.