Quantitative inference of the H2 column densities from 3mm molecular emission: case study towards Orion B
Artikel i vetenskaplig tidskrift, 2020

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.

ISM: clouds

ISM: molecules

methods: statistical

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, Galaktisk astrofysik

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, Galaktisk astrofysik

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 A27

Ämneskategorier

Astronomi, astrofysik och kosmologi

Atom- och molekylfysik och optik

Teoretisk kemi

DOI

10.1051/0004-6361/202037871

Mer information

Senast uppdaterat

2021-01-21