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 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:
- ClustCO.fit : Cluster assignation map from the clustering analysis
based on CO isotopes only.
- ClustFUV.fit : Cluster assignation map from the clustering analysis
based on CO isotopes, HCO+ and CN.
- map12CO.fit : Integrated intensity (9-12km/s) map of the
12CO J=1-0 line.
- map13CO.fit : Integrated intensity (9-12km/s) map of the
13CO J=1-0 line.
- mapC18O.fit : Integrated intensity (9-12km/s) map of the
C18O J=1-0 line.
- mapCN.fit : Integrated intensity (9-12km/s) map of the CN N=1-0 line.
- mapHCOp.fit : Integrated intensity (9-12km/s) map of the
HCO+ J=1-0 line.
Objects:
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RA (2000) DE Designation(s)
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05 41 42.7 -01 54 44 Orion B = NAME Orion B
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 133 7 List of fits images
fits/* . 7 Individual fits images
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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
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Bytes Format Units Label Explanations
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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
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Acknowledgements:
Emeric Bron, emeric.bron(at)obspm.fr
(End) Emeric Bron [ICMM - Spain], Patricia Vannier [CDS] 20-Dec-2017