Title :

Tracers of the ionization fraction in dense and translucent gas: I. Automated exploitation of massive astrochemical model grids

Author(s) :

Bron, Emeric [Auteur correspondant]
Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres [LERMA]
Roueff, Evelyne [Auteur]
Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres [LERMA]
Gerin, Maryvonne [Auteur]
Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres [LERMA]
Pety, Jérôme [Auteur]
Institut de RadioAstronomie Millimétrique [IRAM]
Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres [LERMA]
Gratier, Pierre [Auteur]
FORMATION STELLAIRE 2020
Petit, Franck Le [Auteur]
Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres [LERMA]
Guzman, Viviana [Auteur]
Pontificia Universidad Católica de Chile [UC]
Orkisz, Jan [Auteur]
Onsala Space Observatory [OSO]
Magalhaes, Victor de Souza [Auteur]
Institut de RadioAstronomie Millimétrique [IRAM]
Gaudel, Mathilde [Auteur]
Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres [LERMA]
Vono, Maxime [Auteur]
Signal et Communications [IRIT-SC]
Bardeau, Sébastien [Auteur]
Institut de RadioAstronomie Millimétrique [IRAM]
Chainais, Pierre [Auteur]
Centre de Recherche en Informatique, Signal et Automatique de Lille - UMR 9189 [CRIStAL]
Goicoechea, Javier [Auteur]
Instituto de Física Fundamental [Madrid] [IFF]
Hughes, Annie [Auteur]
Institut de recherche en astrophysique et planétologie [IRAP]
Kainulainen, Jouni [Auteur]
Onsala Space Observatory [OSO]
Languignon, David [Auteur]
Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres [LERMA]
Bourlot, Jacques Le [Auteur]
Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres [LERMA]
Levrier, François [Auteur]
Astrophysique
Liszt, Harvey [Auteur]
National Radio Astronomy Observatory [Charlottesville] [NRAO]
Öberg, Karin [Auteur]
Harvard-Smithsonian Center for Astrophysics [CfA]
Peretto, Nicolas [Auteur]
School of Physics and Astronomy [Cardiff]
Roueff, Antoine [Auteur]
Institut FRESNEL [FRESNEL]
PhyTI [PhyTI]
Sievers, Albrecht [Auteur]
Institut de RadioAstronomie Millimétrique [IRAM]

Journal title :

Astronomy and Astrophysics - A&A

Pages :

A28

Publisher :

EDP Sciences

Publication date :

2021-01

ISSN :

0004-6361

English keyword(s) :

Astrochemistry
ISM: molecules
ISM: clouds
ISM: lines and bands
Methods: statistical
Methods: numerical

HAL domain(s) :

Planète et Univers [physics]

English abstract : [en]

The ionization fraction plays a key role in the physics and chemistry of the neutral interstellar medium, from controlling the coupling of the gas to the magnetic field to allowing fast ion-neutral reactions that drive ...
Show more >The ionization fraction plays a key role in the physics and chemistry of the neutral interstellar medium, from controlling the coupling of the gas to the magnetic field to allowing fast ion-neutral reactions that drive interstellar chemistry. Most estimations of the ionization fraction have relied on deuterated species such as DCO+, whose detection is limited to dense cores representing an extremely small fraction of the volume of the giant molecular clouds they are part of. As large field-of-view hyperspectral maps become available, new tracers may be found. We search for the best observable tracers of the ionization fraction based on a grid of astrochemical models. We build grids of models that sample randomly a large space of physical conditions (unobservable quantities such as gas density, temperature, etc.) and compute the corresponding observables (line intensities, column densities) and the ionization fraction. We estimate the predictive power of each potential tracer by training a Random Forest model to predict the ionization fraction from that tracer, based on these model grids. In both translucent medium and cold dense medium conditions, several observable tracers with very good predictive power for the ionization fraction are found. Several tracers in cold dense medium conditions are found to be better and more widely applicable than the traditional DCO+/HCO+ ratio. We also provide simpler analytical fits for estimating the ionization fraction from the best tracers, and for estimating the associated uncertainties. We discuss the limitations of the present study and select a few recommended tracers in both types of conditions. The method presented here is very general and can be applied to the measurement of any other quantity of interest (cosmic ray flux, elemental abundances, etc.) from any type of model (PDR models, time-dependent chemical models, etc.). (abridged)Show less >

Language :

Anglais

Popular science :

Non

Comment :

29 pages, 15 figures

Collections :

• Centre de Recherche en Informatique, Signal et Automatique de Lille (CRIStAL) - UMR 9189

Source :

Harvested from HAL