Unusually Luminous Giant Molecular Clouds in the Outer Disk of M33

摘要: We use high spatial resolution (~7pc) CARMA observations to derive detailed properties for 8 giant molecular clouds (GMCs) at a galactocentric radius corresponding approximately two CO scale lengths, or ~0.5 optical radii (r25), in the Local Group spiral galaxy M33. At this radius, gas fraction, dust-to-gas ratio and metallicity are much lower than inner part of M33 typical galaxy. This allows us probe impact environment on GMC by comparing our measurements previous data from disk M33, Milky Way other nearby galaxies. The outer roughly fall size-linewidth relation defined extragalactic GMCs, but slightly displaced luminosity-virial mass sense having luminosity compared inferred virial mass. implies different CO-to-H2 conversion factor, which is average factor average. attribute significantly higher measured brightness temperatures ancillary sample likely an effect enhanced radiation levels due massive star formation vicinity target field. Apart temperature, we determine GMCs do not differ those comparison sample. In particular, combined covers same range size, linewidth, GMCs. When however, find even brightest be smaller most their counterparts. may incomplete sampling potentially steeper cloud function larger radii.