Published online by Cambridge University Press: 12 April 2016
Recently, it has been shown that some of nearby spiral galaxies have very massive (107-8Mʘ) and large (several 100 pc - ~ 1 kpc) molecular gas clouds (M51: Rand & Kulkarni 1990; NGC1068: Planesas et al. 1991). Since these clouds are significantly more massive and larger than those of so-called Giant Molecular Clouds (GMCs) found in our Galaxy, they are called Molecular Super-clouds (Rand & Kulkarni 1990; hereafter MSCs). In order to study observational properties of MSCs, we present the results of high-resolution (4”) 12CO(J=1-0) mosaic mapping of central 2.’5 region of the Sbc galaxy M51 using the Nobeyama Millimeter Array (NMA). Our main results are summarized in the followings (Tosaki, Kawabe & Taniguchi 1992).