# The integrated properties of the molecular clouds from the JCMT CO(3-2) High Resolution Survey

## TL;DR

This study presents a comprehensive catalog of over 85,000 molecular clouds in the Milky Way's first quadrant using JCMT CO(3-2) data, revealing their properties, distributions, and scaling relations with significant scatter.

## Contribution

It introduces the first large-scale, high-resolution catalog of molecular clouds with detailed segmentation and analysis of their mass and size distributions.

## Key findings

- Cloud mass distribution follows a truncated power law with a cutoff at ~3 million solar masses.
- Only 35% of clouds are within spiral arms, indicating diverse cloud environments.
- Scaling relations show large intrinsic scatter, similar to other galaxy surveys.

## Abstract

We define the molecular cloud properties of the Milky Way first quadrant using data from the JCMT CO(3-2) High Resolution Survey. We apply the Spectral Clustering for Interstellar Molecular Emission Segmentation (SCIMES) algorithm to extract objects from the full-resolution dataset, creating the first catalog of molecular clouds with a large dynamic range in spatial scale. We identify $>85\,000$ clouds with two clear sub-samples: $\sim35\,500$ well-resolved objects and $\sim540$ clouds with well-defined distance estimations. Only 35% of the cataloged clouds (as well as the total flux encompassed by them) appear enclosed within the Milky Way spiral arms. The scaling relationships between clouds with known distances are comparable to the characteristics of the clouds identified in previous surveys. However, these relations between integrated properties, especially from the full catalog, show a large intrinsic scatter ($\sim0.5$ dex), comparable to other cloud catalogs of the Milky Way and nearby galaxies. The mass distribution of molecular clouds follows a truncated-power law relationship over three orders of magnitude in mass with a form $dN/dM \propto M^{-1.7}$ with a clearly defined truncation at an upper mass of $M_0 \sim 3 \times 10^6~M_\odot$, consistent with theoretical models of cloud formation controlled by stellar feedback and shear. Similarly, the cloud population shows a power-law distribution of size with $dN/dR \propto R^{-2.8}$ with a truncation at $R_0 = 70$ pc.