A Morphological Classification of 18190 Molecular Clouds Identified in $^{12}$CO Data from the MWISP Survey

Abstract

We attempt to visually classify the morphologies of 18190 molecular clouds, which are identified in the 12 CO(1-0) spectral line data over ∼ 450 deg 2 of the second Galactic quadrant from the Milky Way Imaging Scroll Painting project (MWISP). Using the velocity-integrated intensity maps of the 12 CO(1-0) emission, molecular clouds are first divided into unresolved and resolved ones. The resolved clouds are further classified as non-filaments or filaments. Among the 18190 molecular clouds, ∼ 25 % are unresolved, ∼ 64% are non-filaments, and ∼ 11% are filaments. In the terms of the integrated flux of 12 CO(1-0) spectra of the whole 18190 molecular clouds, ∼ 90% are from filaments, ∼ 9% are from non-filaments, and the rest ∼ 1% are from unresolved sources. Although non-filaments are dominant in the number of the discrete molecular clouds, filaments are the main contributor of 12 CO emission flux. We also present the number distributions of physical parameters of the molecular clouds in our catalog, including their angular sizes, velocity spans, peak intensities of 12 CO(1-0) emission, and 12 CO(1-0) total fluxes. We find that there is a systematic difference between the angular sizes of the non-filaments and filaments, with the filaments tending to have larger angular scales. The H 2 column densities of them are not significantly different. We also discuss the observational effects, such as those induced by the finite spatial resolution, beam dilution and line-of-sight projection, on the morphological classification of molecular clouds in our sample.