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We report sensitive imaging observations of the CO J=1-0 line emission in thepowerful high-redshift radio galaxy 4C 41.17 (z=3.8) with the NRAO Very LargeArray (VLA), conducted in order to detect the large concomitant H_2 gasreservoir recently unveiled in this system by De Breuck et al (2005) via theemission of the high excitation J=4-3 line. Our observations fail to detect theJ=1-0 line but yield sensitive lower limits on the R_43=(4-3)/(1-0) brightnesstemperature ratio of R_43 ~ 0.55 - >1.0 for the bulk of the H_2 gas mass. Suchhigh ratios are typical of the high-excitation molecular gas phase ``fueling''the star formation in local starbursts, but quite unlike these objects, much ofthe molecular gas in 4C 41.17 seems to be in such a state, and thusparticipating in the observed starburst episode. The widely observed and uniqueassociation of highly excited molecular gas with star forming sites allows COline emission with large (high-J)/(low-J) intensity ratios to serve as anexcellent ``marker'' of the spatial distribution of star formation in distantdust-obscured starbursts, unaffected by extinction.Comment: 7 Pages including 8 PostScript figures. Accepted for publication in  Astronomy & Astrophysic

A sensitive search for CO J = 1–0 emission in 4C 41.17: high-excitation molecular gas at z = 3.8