(CO)-C-12(J=1-0) AND (CO)-C-13(J=1-0) MAPPING OF THE STARBURST GALAXYM82

We have mapped the central 1 kpc region of the nearby starburst galaxy M82 in both the (CO)-C-12 (J = 1-0) and (CO)-C-13(J = 1-0) emission l ines under the same angular resolution (similar to 7 '' x 6 ''). The i ntensity ratio (R) of (CO)-C-12 (J = 1-0) to (CO)-C-13 (J = 1-0) emiss ion shows the significant spatial variation: R similar or equal to 35- 40 (the NE lobe), R similar or equal to 20-25 (the SW lobe), and R > 7 0 (the 2.2 mu m secondary peak). These values are significantly higher than those of giant molecular clouds in our Galaxy and molecular gas in other normal spiral galaxies. We also find that a very high ratio ( R > 90) is achieved around the brightest radio continuum source, 41.9 + 58, which is considered to be a supernova remnant (or remnants). Bas ed on the LTE model, we show that the molecular gas in M82 tends to be optically thin, even for the (CO)-C-12 emission; its optical depth is a few or less. The smaller optical depths may naturally explain the h igher R values observed in M82. We discuss the possibility that a supe rwind causes the formation of such clouds.