(CO)-C-12 (3-2) AND (1-0) EMISSION-LINE OBSERVATIONS OF NEARBY STARBURST STARBURST GALAXY NUCLEI

New measurements of the (CO)-C-12 (1 - 0) and (CO)-C-12 (3 - 2) line e mission are presented for the nuclei of seven nearby starburst galaxie s selected from a complete sample of 21 nearby starburst galaxies for which the nuclear star formation rates are measured to be comparable t o the archetype starburst galaxies M82 and NGC 253. The new observatio ns capitalize on the coincidence between the beam size of the 45 m Nob eyama telescope at 115 GHz and that of the 15 m James Clerk Maxwell Te lescope at 345 GHz to measure the value of the (CO)-C-12 (3 - 2)/(1 - 0) emission line ratio in a 15'' (less-than-or-equal-to 2.5 kpc) diame ter region centered on the nuclear starburst. In principle, the (CO)-C -12 (3 - 2)/(1 -0) emission line ratio provides a measure of temperatu re and optical depth for the (CO)-C-12 gas. The error weighted mean va lue of the (CO)-C-12 (3 - 2)/(1 - 0) emission line ratio measured for the seven starburst galaxy nuclei is 0.64+/-0.06. The (CO)-C-12 (3 - 2 )/(1 - 0) emission line ratio measured for the starburst galaxy nuclei is significantly higher than the average value measured for molecular gas in the disk of the Galaxy, implying warmer temperatures for the m olecular gas in starburst galaxy nuclei. On the other hand, the (CO)-C -12 (3 - 2)/(1 - 0) emission line ratio measured for the starburst gal axy nuclei is not as high as would be expected if the molecular gas we re hot, >20 K, and optically thin, tau much less than 1. The total mas s of molecular gas contained within the central 1.2-2.8 kpc diameter r egion of the starburst galaxy nuclei ranges from 10(8) to 10(9) While substantial, the molecular gas mass represents only a small percentage , approximately 9%-16%, of the dynamical mass in the same region.