[EPR2003] 148 , the SIMBAD biblio

We present the first interferometric ¹²CO (J=1⟶0) map of the entire Hα disk of M33. The 13" diameter synthesized beam corresponds to a linear resolution of 50 pc, sufficient to distinguish individual giant molecular clouds (GMCs). From these data we generated a catalog of 148 GMCs with an expectation that no more than 15 of the sources are spurious. The catalog is complete down to GMC masses of 1.5x10⁵M_☉and contains a total mass of 2.3x10⁷M_☉. Single-dish observations of CO in selected fields imply that our survey detects ∼50% of the CO flux, hence that the total molecular mass of M33 is 4.5x10⁷M_☉, approximately 2% of the H I mass. The GMCs in our catalog are confined largely to the central region (R<4 kpc). They show a remarkable spatial and kinematic correlation with overdense H I filaments; the geometry suggests that the formation of GMCs follows that of the filaments. The GMCs exhibit a mass spectrum dN/dM∝M^–2.6±0.3, considerably steeper than that found in the Milky Way and in the LMC. Combined with the total mass, this steep function implies that the GMCs in M33 form with a characteristic mass of ∼7x10⁴ M_☉. More than 2/3 of the GMCs have associated H II regions, implying that the GMCs have a short quiescent period. Our results suggest the rapid assembly of molecular clouds from atomic gas, with prompt onset of massive star formation.