Northern Galactic Molecular Cloud Clumps in Hi-GAL: Dense Gas Map and Environmental Trends

TL;DR

This study maps dense molecular gas in the Galactic plane using Hi-GAL survey data, revealing how clump properties vary with Galactocentric radius to inform high-mass star formation understanding.

Contribution

It provides a 3D dense gas map of the Galactic plane and analyzes the properties and distribution of molecular cloud clumps with respect to their galactocentric distance.

Findings

Clump masses decrease with Galactocentric radius.

Clump radii are independent of Galactocentric radius.

Identified nearly 20,000 clumps with many having well-constrained distances.

Abstract

In the quest to understand high-mass star formation, it is necessary to understand that from which the high-mass stars will form -- the dense molecular gas clouds and clumps. The Herschel infrared GALactic plane survey (Hi-GAL) is a comprehensive survey of thermal dust emission that can be used to characterize the properties and Galactic distribution of molecular gas. We have analyzed the survey maps within the Galactic longitude range $10^\circ < \ell < 56^\circ$ and have transformed these 2D maps into a 3D dense gas map of the Galactic plane using distance probability density functions. This range corresponds to the extent of the Galactic Ring Survey (GRS), which provided the majority of our line-of-sight velocities, and thus kinematic distances. In this section of Hi-GAL, we identify 19,886 clumps, out of which 10,124 have, at minimum, a kinematic distance, and 5,405 have their distances well constrained through Bayesian techniques. Of those with well-constrained distances, clump masses tend to decrease with Galactocentric radius, whereas clump radii are independent of Galactocentric radius.