Quantitative inference of the H2 column densities from 3mm molecular emission: case study towards Orion B
Artikel i vetenskaplig tidskrift, 2021
Context. Based on the finding that molecular hydrogen is unobservable in cold molecular clouds, the column density measurements of molecular gas currently rely either on dust emission observation in the far-infrared, which requires space telescopes, or on star counting, which is limited in angular resolution by the stellar density. The (sub)millimeter observations of numerous trace molecules can be effective using ground-based telescopes, but the relationship between the emission of one molecular line and the H-2 column density is non-linear and sensitive to excitation conditions, optical depths, and abundance variations due to the underlying physico- chemistry.Aims. We aim to use multi-molecule line emission to infer the H-2 molecular column density from radio observations.Methods. We propose a data-driven approach to determine the H-2 gas column densities from radio molecular line observations. We use supervised machine-learning methods (random forest) on wide-field hyperspectral IRAM-30m observations of the Orion B molecular cloud to train a predictor of the H-2 column density, using a limited set of molecular lines between 72 and 116 GHz as input, and the Herschel-based dust-derived column densities as "ground truth" output.Results. For conditions similar to those of the Orion B molecular cloud, we obtained predictions of the H-2 column density within a typical factor of 1.2 from the Herschel-based column density estimates. A global analysis of the contributions of the different lines to the predictions show that the most important lines are (CO)-C-13(1-0), (CO)-C-12(1-0), (CO)-O-18(1-0), and HCO+(1-0). A detailed analysis distinguishing between diffuse, translucent, filamentary, and dense core conditions show that the importance of these four lines depends on the regime, and that it is recommended that the N2H+(1-0) and CH3OH(2(0)-1(0)) lines be added for the prediction of the H-2 column density in dense core conditions.Conclusions. This article opens a promising avenue for advancing direct inferencing of important physical parameters from the molecular line emission in the millimeter domain. The next step will be to attempt to infer several parameters simultaneously (e.g., the column density and far-UV illumination field) to further test the method.
methods: statistical
ISM: clouds
ISM: molecules
Författare
Pierre Gratier
Université de Bordeaux
Jerome Pety
Institut de Radioastronomie Millimétrique (IRAM)
Université de recherche Paris Sciences et Lettres
Emeric Bron
Université de recherche Paris Sciences et Lettres
Antoine Roueff
Aix-Marseille Université
Jan Orkisz
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
Maryvonne Gerin
Université de recherche Paris Sciences et Lettres
Victor de Souza Magalhaes
Institut de Radioastronomie Millimétrique (IRAM)
Mathilde Gaudel
Université de recherche Paris Sciences et Lettres
Maxime Vono
Université de Toulouse
Sebastien Bardeau
Institut de Radioastronomie Millimétrique (IRAM)
Jocelyn Chanussot
Université Grenoble Alpes
Pierre Chainais
Université de Lille
Javier R. Goicoechea
CSIC - Instituto de Fisica Fundamental (IFF)
Viviana V. Guzman
Pontificia Universidad Catolica de Chile
Annie Hughes
Universite Paul Sabatier Toulouse III
Jouni Kainulainen
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
David Languignon
Université de recherche Paris Sciences et Lettres
Jacques Le Bourlot
Université de recherche Paris Sciences et Lettres
Franck Le Petit
Université de recherche Paris Sciences et Lettres
Francois Levrier
Université de recherche Paris Sciences et Lettres
Harvey Liszt
National Radio Astronomy Observatory
Nicolas Peretto
Cardiff University
Evelyne Rouefe
Université de recherche Paris Sciences et Lettres
Albrecht Sievers
Institut de Radioastronomie Millimétrique (IRAM)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 645 A27Ämneskategorier
Astronomi, astrofysik och kosmologi
Atom- och molekylfysik och optik
Teoretisk kemi
DOI
10.1051/0004-6361/202037871