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J/A+A/610/A12       Clustering the Orion B giant molecular cloud   (Bron+, 2018)

Clustering the Orion B giant molecular cloud based on its molecular emission. Bron E., Daudon C., Pety J., Levrier F., Gerin M., Gratier P., Orkisz J. H., Guzman V., Bardeau S., Goicoechea J. R., Liszt H., Oeberg K., Peretto N., Sievers A., Tremblin P. <Astron. Astrophys. 610, A12 (2018)> =2018A&A...610A..12B (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Molecular clouds ; Spectrophotometry ; Carbon monoxide Keywords: astrochemistry - ISM: molecules - ISM: clouds - ISM: structure - methods: statistical - ISM: individual objects: Orion B Abstract: Previous attempts at segmenting molecular line maps of molecular clouds have focused on using position-position-velocity data cubes of a single molecular line to separate the spatial components of the cloud. In contrast, wide field spectral imaging over a large spectral bandwidth in the (sub)mm domain now allows one to combine multiple molecular tracers to understand the different physical and chemical phases that constitute giant molecular clouds (GMCs). We aim at using multiple tracers (sensitive to different physical processes and conditions) to segment a molecular cloud into physically/ chemically similar regions (rather than spatially connected components), thus disentangling the different physical/chemical phases present in the cloud. We use a machine learning clustering method, namely the Meanshift algorithm, to cluster pixels with similar molecular emission, ignoring spatial information. Clusters are defined around each maximum of the multidimensional probability density function (PDF) of the line integrated intensities. Simple radiative transfer models were used to interpret the astrophysical information uncovered by the clustering analysis. A clustering analysis based only on the J=1-0 lines of three isotopologues of CO proves sufficient to reveal distinct density/column density regimes (nH∼100cm-3, ∼500cm-3, and >1000cm-3), closely related to the usual definitions of diffuse, translucent and high-column-density regions. Adding two UV-sensitive tracers, the J=1-0 line of HCO+ and the N=1-0 line of 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 a photochemical enrichment effect. We also find a tail of high CN/HCO+ intensity ratio in UV-illuminated regions. Finer distinctions in density classes (nH∼7103cm-3, ∼4104cm-3) for the densest regions are also identified, likely related to the higher critical density of the CN and HCO+ (1-0) lines. These distinctions are only possible because the high-density regions are spatially resolved. Molecules are versatile tracers of GMCs because their line intensities bear the signature of the physics and chemistry at play in the gas. The association of simultaneous multi-line, wide-field mapping and powerful machine learning methods such as the Meanshift clustering algorithm reveals how to decode the complex information available in these molecular tracers. Description: Integrated line intensities maps (in the 9-12km/s range) of the Orion B molecular cloud in 12CO(1-0), 13CO(1-0), C18O(1-0), CN(1-0), HCO+(1-0), used as basis for the clustering analysis presented in the paper. Maps of the cluster attributions of each pixel resulting from the two clustering analyses presented (based on CO isotopes only, and based on CO isotopes, HCO+ and CN) are also included. Description of the fits files: - : Cluster assignation map from the clustering analysis based on CO isotopes only. - : Cluster assignation map from the clustering analysis based on CO isotopes, HCO+ and CN. - : Integrated intensity (9-12km/s) map of the 12CO J=1-0 line. - : Integrated intensity (9-12km/s) map of the 13CO J=1-0 line. - : Integrated intensity (9-12km/s) map of the C18O J=1-0 line. - : Integrated intensity (9-12km/s) map of the CN N=1-0 line. - : Integrated intensity (9-12km/s) map of the HCO+ J=1-0 line. Objects: ----------------------------------------------------- RA (2000) DE Designation(s) ----------------------------------------------------- 05 41 42.7 -01 54 44 Orion B = NAME Orion B ----------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file list.dat 133 7 List of fits images fits/* 0 7 Individual fits images
See also: J/ApJ/559/307 : Sub-mm mapping in Orion B molecular cloud (Johnstone+, 2001) J/ApJ/639/259 : Sub-mm clumps in Orion B South mol. cloud (Johnstone+, 2006) J/ApJ/691/1560 : Dense core survey in the Orion B cloud (Ikeda+, 2009) J/ApJ/817/167 : JCMT Gould Belt Survey: dense cores in Orion B (Kirk+, 2016) Byte-by-byte Description of file: list.dat
Bytes Format Units Label Explanations
1- 9 F9.5 deg RAdeg Right ascension of center (J2000) 10- 18 F9.5 deg DEdeg Declination of center (J2000) 20- 22 I3 --- Nx Number of pixels along X-axis 24- 26 I3 --- Ny Number of pixels along Y-axis 28- 31 I4 Kibyte size Size of FITS file 33- 44 A12 --- FileName Name of FITS file, in subdirectory fits 46-133 A88 --- Title Title of the FITS file
Acknowledgements: Emeric Bron, emeric.bron(at)
(End) Emeric Bron [ICMM - Spain], Patricia Vannier [CDS] 20-Dec-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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