Clustering the Orion B giant molecular cloud based on its molecular emission

Abstract

Previous attempts at segmenting molecular line maps of molecular clouds have focused on using position-position-velocity data cubes of a single line to separate the spatial components of the cloud. In contrast, wide field spectral imaging with large spectral bandwidth in the (sub)mm domain now allows to combine multiple molecular tracers to understand the different physical and chemical phases that constitute giant molecular clouds. We aim at using multiple tracers (sensitive to different physical processes) to segment a molecular cloud into physically/chemically similar regions (rather than spatially connected components). We use a machine learning clustering method (the Meanshift algorithm) to cluster pixels with similar molecular emission, ignoring spatial information. Simple radiative transfer models are used to interpret the astrophysical information uncovered by the clustering. A clustering analysis based only on the J=1-0 lines of 12CO, 13CO and C18O reveals distinct density/column density regimes (nH~100, 500, and >1000 cm-3), closely related to the usual definitions of diffuse, translucent and high-column-density regions. Adding two UV-sensitive tracers, the (1-0) lines of HCO+ and CN, allows us to distinguish two clearly distinct chemical regimes, characteristic of UV-illuminated and UV-shielded gas. The UV-illuminated regime shows overbright HCO+ and CN emission, which we relate to photochemical enrichment. We also find a tail of high CN/HCO+ intensity ratio in UV-illuminated regions. Finer distinctions in density classes (nH~7E3, and 4E4 cm-3) for the densest regions are also identified, likely related to the higher critical density of the CN and HCO+ (1-0) lines. The association of simultaneous multi-line, wide-field mapping and powerful machine learning methods such as the Meanshift algorithm reveals how to decode the complex information available in molecular tracers.

Accepted for publication in A&A. 26 pages and 23 figures. The associated data products will soon be available at http://www.iram.fr/~pety/ORION-B

References in corpus (18)

• The distance to the Orion Nebula
• Bias-free Measurement of Giant Molecular Cloud Properties
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• The anatomy of the Orion B Giant Molecular Cloud: A local template for studies of nearby galaxies
• A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry
• The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds II: the Spatial Distribution and Demographics of Dusty Young Stellar Objects
• Testing the universality of the star formation efficiency in dense molecular gas
• Graph-based interpretation of the Molecular Interstellar Medium Segmentation
• Turbulence and star formation efficiency in molecular clouds: solenoidal versus compressive motions in Orion B
• Electron Excitation of High Dipole Moment Molecules Reexamined
• On the chemistry and distribution of HOC+ in M82: More evidence for extensive PDRs
• Dissecting the molecular structure of the Orion B cloud: Insight from Principal Component Analysis
• SCUBA observations of the Horsehead Nebula - what did the horse swallow?
• The JCMT Gould Belt Survey: A First Look at Dense Cores in Orion B
• Molecular hydrogen in the circumstellar environments of Herbig Ae/Be stars probed by FUSE
• The detectability of mm-wave molecular rotational transitions
• Geometry-Independent Determination of Radial Density Distributions in Molecular Cloud Cores and Other Astronomical Objects

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