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

TL;DR

This study uses a Minimum Spanning Tree algorithm to analyze the clustering of far-infrared sources in the Galaxy, revealing different spatial distributions linked to star formation processes and source properties.

Contribution

It introduces a novel application of MST to characterize the spatial distribution of Galactic far-IR sources and their relation to star formation activity.

Findings

Over half of clustered sources are associated with HII regions and dark clouds.

Sources at shorter wavelengths are more densely clustered around HII regions.

Longer wavelength sources are more dispersed and form looser groups.

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.