An outer galaxy molecular cloud catalog

We have generated a molecular cloud catalog from the Five College Radio Astronomy Observatory Outer Galaxy Survey of (CO)-C-12 (J = 1-0) emission using a two-phase object identification procedure. The first phase consists of grouping pixels into contiguous structures above a radiation temperature threshold of 0.8 K. The second phase decomposes the first-phase objects by an enhanced version of the CLUMPFIND algorithm, using dynamic thresholding, and again with a threshold of 0.8 K used for discrimination. A detailed comparison of our method with the CLUMPFIND algorithm is given, highlighting the advantages of the use of dynamic (rather than quantized) thresholding. Basic attributes of the clouds coordinates, bounding boxes, integrated intensities, peak observed temperatures are tabulated in the catalog. A two-dimensional elliptical Gaussian is fitted to the velocity-integrated map of each cloud; the major and minor axis sizes and major axis position angles thus derived are included in the catalog. To the spatially integrated emission line of each cloud, a Gaussian pro le is fitted to measure the global linewidth. Model Gaussian clouds, truncated at 0.8 K, are examined to determine the effects of biases on measured quantities, induced by truncation. Coupled with detailed analysis of the cataloged clouds, statistical corrections for the effects of truncation on measured sizes, linewidths, and integrated intensities are derived and applied, along with corrections for the effects of finite resolution on the measured attributes. The cataloged emission accounts for 76.4% of the total emission in the Outer Galaxy Survey. The deficit is shown to arise mainly from low-intensity emission on the periphery of larger objects, rather than from a large number of small and/or low-intensity features. From the measured parameters, Gaussian reconstructions of the emission are carried out, and these compare favorably to the raw data. A detailed analysis of the decomposition in complex regions is performed, showing that severe truncation at levels much in excess of 0.8 K is countered by the operation of a thermostat, resulting in concatenation of emission into a larger object if severe blending is present, rather than the identification of a number of smaller, more heavily truncated objects. Two other tests are carried out: ( 1) an association test that examines the utility of using the decomposed (CO)-C-12 (J = 1-0) emission, in comparison to CS emission, to identify possible sites of star formation as traced by IRAS point sources; (2) a test comparison of (CO)-C-12 and (CO)-C-13 decompositions to gauge the effects of emission saturation and blending. Overall, the results of these two tests show that emission enhancements in (CO)-C-12 (J = 1-0) emission, induced by internal heating by embedded star formation, are in general usefully recorded in the decomposition, but that emission blending and saturation on scales of similar tofew arcminutes in complex regions can limit the precision to which associations with other tracers can be made. A statistical approach to source association that makes good use of the information contained in the catalog is developed and described. The new (CO)-C-12 cloud catalog, as a concise description of the OGS data, will facilitate intercomparisons of molecular clouds with other ISM components, available at comparable resolution within the Canadian Galactic Plane Survey. The catalog covers the Galactic longitude range 102 = 5 to 141 = 5, Galactic latitude range -3degrees to +5.degrees4, and lsr velocity range + 20.8 to -120.2 km s(-1) and contains 14, 592 objects. Due to its size, and for ease of access, the catalog is made available in electronic form.