We observed 146 Galactic clumps in HCN ( 4-3 ) and CS ( 7-6 ) with the Atacama Submillimeter Telescope Experiment ( ASTE ) 10-m telescope .
A tight linear relationship between star formation rate and gas mass traced by dust continuum emission was found for both Galactic clumps and the high redshift ( \textit { z } > 1 ) star forming galaxies ( SFGs ) , indicating a constant gas depletion time of \sim 100 Myr for molecular gas in both Galactic clumps and high z SFGs .
However , low z galaxies do not follow this relation and seem to have a longer global gas depletion time .
The correlations between total infrared luminosities ( L _ { TIR } ) and molecular line luminosities ( L ^ { \prime } _ { mol } ) of HCN ( 4-3 ) and CS ( 7-6 ) are tight and sublinear extending down to clumps with L _ { TIR } \sim 10 ^ { 3 } L _ { \sun } .
These correlations become linear when extended to external galaxies .
A bimodal behavior in the L _ { TIR } –L ^ { \prime } _ { mol } correlations was found for clumps with different dust temperature , luminosity-to-mass ratio , and \sigma _ { line } / \sigma _ { vir } .
Such bimodal behavior may be due to evolutionary effects .
The slopes of L _ { TIR } –L \arcmin _ { mol } correlations become more shallow as clumps evolve .
We compared our results with lower J transition lines in ( 40 ) .
The correlations between clump masses and line luminosities are close to linear for low effective excitation density tracers but become sublinear for high effective excitation density tracers for clumps with L _ { TIR } larger than L _ { TIR } \sim 10 ^ { 4.5 } L _ { \sun } .
High effective excitation density tracers can not linearly trace the total clump masses , leading to a sublinear correlations for both M _ { clump } –L \arcmin _ { mol } and L _ { TIR } –-L \arcmin _ { mol } relations .