We analyze the spatially resolved ( 250 pc scales ) and integrated star formation ( SF ) law in the local luminous infrared galaxy ( LIRG ) IC 4687 .
This is one of the first studies of the SF law on a starburst LIRG at these small spatial scales .
We combined new interferometric ALMA CO ( 2–1 ) data with existing HST /NICMOS Pa \alpha narrowband imaging and VLT/SINFONI near-IR integral field spectroscopy to obtain accurate extinction-corrected SF rate ( SFR ) and cold molecular gas surface densities ( \Sigma _ { gas } and \Sigma _ { SFR } ) .
We find that IC 4687 forms stars very efficiently with an average depletion time ( t _ { dep } ) of 160 Myr for the individual 250 pc regions .
This is approximately one order of magnitude shorter than the t _ { dep } of local normal spirals and also shorter than that of main-sequence high- z objects , even when we use a Galactic \alpha _ { CO } conversion factor .
This result suggests a bimodal SF law in the \Sigma _ { SFR } \propto \Sigma _ { gas } ^ { N } representation .
A universal SF law is recovered if we normalize the \Sigma _ { gas } by the global dynamical time .
However , at the spatial scales studied here , we find that the SF efficiency ( or t _ { dep } ) does not depend on the local dynamical time for this object .
Therefore , an alternative normalization ( e.g. , free-fall time ) should be found if a universal SF law exists at these scales .