Evolution of molecular clouds on galaxy-cloud scale revealed by gravitational network analysis : High-mass clouds may deplete nearby gas via accretion or merging

TL;DR

This study models molecular clouds in galaxy NGC 628 as a gravitational network, revealing how high-mass clouds tend to be more isolated and may deplete nearby gas through accretion or merging, influencing their evolution.

Contribution

It introduces a novel gravitational network analysis of molecular clouds, linking their physical properties with network metrics to understand their formation and evolution.

Findings

High-mass clouds are less clustered and more isolated.

Less evolved, lower-mass clouds are in tighter subnetworks.

High-mass clouds may deplete nearby gas via accretion or merging.

Abstract

Observations show that molecular gas in spiral galaxies is organized into a network of interconnected systems through the gravitational coupling of multi-scale hub-filament structures. Building on this picture, we model molecular gas in the galaxy NGC 628 as a gravitational network, where molecular clouds are represented as nodes. Through analyzing this network, we can characterize both the gravitational interactions and the physical properties of the clouds using geometry-based network metrics. A strong correlation is observed between the geometric and physical properties of the nodes (clouds). High-mass clouds tend to exhibit less clustering and greater average separations, suggesting that they generally have fewer neighbors. During their formation and evolution, high-mass clouds may deplete nearby gas via accretion or merging, leading to more isolated characteristics within the network. This aligns with observations showing a decrease in the virial ratio of molecular clouds as their mass increases. For clouds at different evolutionary stages, less evolved clouds with lower mass are typically found in tighter gravitational subnetworks, with closer proximity to neighboring clouds. As a result, they are more prone to accretion or merging during evolution.