Arclike distribution of high CO (J=3-2)/CO (J=1-0) ratio gas surrounding central star cluster of the supergiant HII region NGC 604

We report the discovery of a high CO (J = 3-2)/CO (J = 1-0 ) ratio gas with an arclike distribution (high ratio gas arc) surrounding the central star cluster of the supergiant H ii region NGC 604 in the nearby spiral galaxy M33, based on multi- J CO observations of a 5' x 5' region of NGC 604 conducted using the ASTE 10 m and NRO 45 m telescopes. The discovered high- ratio gas arc extends to the southeast- northwest direction with a size of similar to 200 pc. The western part of the high- ratio gas arc closely coincides with the shells of the H (II) regions traced by Ha and radio continuum peaks. The CO (J = 3-2)/CO (J = 1-0 ) ratio, R3-2/1-0, ranges between 0.3 and 1.2 in the observed region, and the R3-2/1-0 values of the high- ratio gas arc are around or higher than unity, indicating very warm (T-kin >= 60 K) and dense (n(H2) >= 10(3) -10(4) cm(-3)) conditions of the high- ratio gas arc. We suggest that the dense gas formation and second-generation star formation occur in the surrounding gas compressed by the stellar wind and/or supernova of the first-generation stars of NGC 604, i. e., the central star cluster of NGC 604.