2005A&A...444..813P

We report sensitive imaging observations of the CO J=1-0 line emission in the powerful high-redshift radio galaxy 4C41.17 (z=3.8) with the NRAO Very Large Array (VLA), conducted in order to detect the large concomitant H₂ gas reservoir recently unveiled in this system by De Breuck et al.(2005) via the emission of the high excitation J=4-3 line. Our observations fail to detect the J=1-0 line but yield sensitive lower limits on the R₄₃=(4-3)/(1-0) brightness temperature ratio of R₄₃∼0.55-γ1.0 for the bulk of the H₂ gas mass. Such high ratios are typical of the high-excitation molecular gas phase ``fueling'' the star formation in local starbursts, but quite unlike these objects, much of the molecular gas in 4C41.17 seems to be in such a state, and thus participating in the observed starburst episode. The widely observed and unique association of highly excited molecular gas with star forming sites allows CO line emission with large (high-J)/(low-J) intensity ratios to serve as an excellent ``marker'' of the spatial distribution of star formation in distant dust-obscured starbursts, unaffected by extinction.