X-factors in a 2-component model Assumptions:   Orion-like high excitation component (probably not needed with denser coverage of CO ladder  Herschel)   Radiation pressure supported disk  L FIR /M(star forming gas) = constant (observed: L FIR /L HCN = constant; e.g., Gao & Solomon, Wu et al.) Results:   X-factors in (U)LIRGs dominated by dense, star-forming gas   X-factors have values of the order 2  4 (i.e., significantly higher than the Downes/Solomon value of 0.8) 37 Molecular gas in (U)LIRGs
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