Clustering Properties of Far-Infrared Sources in Hi-GAL Science Demonstration Phase Fields

Abstract

We use a Minimum Spanning Tree algorithm to characterize the spatial distribution of Galactic Far-IR sources and derive their clustering properties. We aim to reveal the spatial imprint of different types of star forming processes, e.g. isolated spontaneous fragmentation of dense molecular clouds, or events of triggered star formation around HII regions, and highlight global properties of star formation in the Galaxy. We plan to exploit the entire Hi-GAL survey of the inner Galactic plane to gather significant statistics on the clustering properties of star forming regions, and to look for possible correlations with source properties such as mass, temperature or evolutionary stage. In this paper we present a pilot study based on the two 2x2 square degree fields centered at longitudes l=30 and l=59 obtained during the Science Demonstration Phase (SDP) of the Herschel mission. We find that over half of the clustered sources are associated with HII regions and infrared dark clouds. Our analysis also reveals a smooth chromatic evolution of the spatial distribution where sources detected at short-wavelengths, likely proto-stars surrounded by warm circumstellar material emitting in the far-infrared, tend to be clustered in dense and compact groups around HII regions while sources detected at long-wavelengths, presumably cold and dusty density enhancements of the ISM emitting in the sub-millimeter, are distributed in larger and looser groups.

17 pages, 9 figures, accepted for publication in ApJ

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• The Earliest Phases of Star Formation (EPoS): A Herschel Key Program - The precursors to high-mass stars and clusters
• Extreme infrared variables from UKIDSS - II. an end-of-survey catalogue of eruptive YSOs and unusual stars
• Young Stellar Objects in the Massive Star-Forming Regions W51 and W43
• The JCMT Gould Belt Survey: Dense Core Clusters in Orion B
• Young Stellar Objects in the Massive Star Forming Region W49
• Looking for phase-space structures in star-forming regions: An MST-based methodology
• On the shape of the mass-function of dense clumps in the Hi-GAL fields. I. SED determination and global properties of the mass-functions
• Cloud Disruption via Ionized Feedback: Tracing Pillar Dynamics in Vulpecula
• Source clustering in the Hi-GAL survey determined using a minimum spanning tree method
• A cluster of outflows in the Vulpecula Rift
• Large-scale latitude distortions of the inner Milky Way Disk from the Herschel/Hi-GAL Survey