Hot gas in the nucleus of M82 - (C-12)O and (C-13)O J = 3-2 observations

Observations of the J = 3-2 transitions of (C-12)O and (C-13)O in the starburst galaxy M82 are reported. The (C-12)O J = 3-2 transition in the nuclear region is detected and mapped at 22-arcsec resolution. The high main beam brightness temperature of the line, 6.4 K, when compared to the J = 1-0 and J = 2-1 intensities, requires a hot moderately optically thin gas. There are about 10 to the 8th solar masses of warm molecular gas within a radius of 360 pc of M82. The low optical depths and high densities required to excite the J = 3-2 transition may imply sheetlike or filamentary clumping. 31 refs.