Hierarchical Structure of YSO Clusters in the W40 and Serpens South Region: Group Extraction and Comparison with Fractal Clusters

Abstract

Young stellar clusters are believed to inherit the spatial distribution like hierarchical structures of their natal molecular cloud during their formation. However, the change of the structures between the cloud and the young clusters is not well constrained observationally. We select the W40 - Serpens South region (~ 7 $\times$ 9 pc${}^2$) of the Aquila Rift as a testbed and investigate hierarchical properties of spatial distribution of young stellar objects (YSOs) in this region. We develop a minimum spanning tree (MST)-based method to group stars into several levels by successively cutting down edges longer than an algorithmically determined critical value. A total of 832 YSOs are divided into 5 levels with 23 groups. For describing the hierarchical properties in a controlled way, we construct a set of synthetic source distributions at various fractal dimensions, and apply the same method to explore their group characters. By comparing the $Q$ parameter and the surface density profiles of the observed and the synthetic data, we find that the YSO observation matches spatial patterns from multi-fractal dimensions. In the periphery region where the molecular clouds are more diffuse, the YSO structure is close to a fractal dimension of 2.0, while in the core regions the fractal dimensions are close to 1.6 and 1.4 for the W40 and the Serpens South regions, respectively. Therefore, the YSOs may inherit the fractal pattern of the dense part of the molecular clouds, but such pattern dissipates slowly in several Myr.

12 pages, 9 figures, Submitted to MNRAS

References in corpus (8)

• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• The Spatial Structure of Young Stellar Clusters. I. Subclusters
• Clustered and Triggered Star Formation in W5: Observations with Spitzer
• The Spitzer Gould Belt Survey of Large Nearby Interstellar Clouds: Discovery of a Dense Embedded Cluster in the Serpens-Aquila Rift
• The ALMA View of the OMC1 Explosion in Orion
• On the dynamics and survival of fractal clouds in galactic winds
• Understanding formation of young, distributed low-mass stars and clusters in the W4 cloud complex
• Deep Near-Infrared Survey Toward the W40 and Serpens South Region in Aquila Rift: A Comprehensive Catalog of Young Stellar Objects

Cited by in corpus (3)

• Cloud structure and young star distribution in the Dragonfish complex
• FIRESTORM I: Stellar Feedback and Gas Kinematics in the Evolved W40 Hub-Filament System
• S2D2: Small-scale Significant substructure DBSCAN Detection II. Tracing episodes and gradients of star formation activity