2018A&A...610A..12B


Query : 2018A&A...610A..12B

2018A&A...610A..12B - Astronomy and Astrophysics, volume 610A, 12-12 (2018/2-1)

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., OBERG K., PERETTO N., SIEVERS A. and TREMBLIN P.

Abstract (from CDS):

Context. 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).
Aims. 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.
Methods. 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.
Results. 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∼7x103cm–3, ∼4x104cm–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.
Conclusions. 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.

Abstract Copyright: © ESO, 2018

Journal keyword(s): astrochemistry - ISM: molecules - ISM: clouds - ISM: structure - methods: statistical - ISM: individual objects: Orion B

VizieR on-line data: <Available at CDS (J/A+A/610/A12): list.dat fits/*>

Simbad objects: 10

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Number of rows : 10
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 * zet Ori ** 05 40 45.52666 -01 56 33.2649 0.50 1.56 1.77 1.85 2.05 O9.7Ib+B0III 344 0
2 [WNB2006] B33-SMM1 smm 05 40 54.0 -02 27 32           ~ 5 0
3 NAME Horsehead Nebula DNe 05 40 59.0 -02 27 30           ~ 491 0
4 IC 434 HII 05 41 -02.5           ~ 85 1
5 HGBS J054107.2-022721 Y*? 05 41 07.0 -02 27 21           ~ 10 0
6 NGC 2023 RNe 05 41 37.9 -02 15 52           ~ 610 1
7 NAME Ori B MoC 05 41 43.0 -01 54 44           ~ 1291 0
8 NGC 2024 Cl* 05 41 43 -01 50.5           ~ 1119 1
9 IC 435 RNe 05 43 00.5 -02 18 45           ~ 44 0
10 HD 38087 ** 05 43 00.5754723576 -02 18 45.389406240 7.96 8.40 8.29 8.06 7.89 B3II 160 1

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2022.11.29-16:19:41

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