Title :

Bias versus variance when fitting multi-species molecular lines with a non-LTE radiative transfer model
Application to the estimation of the gas temperature and volume density

Author(s) :

Roueff, Antoine [Auteur correspondant]
Institut des Matériaux, de Microélectronique et des Nanosciences de Provence [IM2NP]
Pety, Jérôme [Auteur]
LERMA Cergy [LERMA]
Institut de RadioAstronomie Millimétrique [IRAM]
Gerin, Maryvonne [Auteur]
LERMA Cergy [LERMA]
Ségal, Léontine [Auteur]
Institut des Matériaux, de Microélectronique et des Nanosciences de Provence [IM2NP]
Institut de RadioAstronomie Millimétrique [IRAM]
Goicoechea, Javier [Auteur]
Instituto de Física Fundamental [Madrid] [IFF]
Liszt, Harvey [Auteur]
National Radio Astronomy Observatory [Charlottesville] [NRAO]
Gratier, Pierre [Auteur]
Laboratoire d'Astrophysique de Bordeaux [Pessac] [LAB]
Bešlić, Ivana [Auteur]
LERMA Cergy [LERMA]
Einig, Lucas [Auteur]
GIPSA - Signal Images Physique [GIPSA-SIGMAPHY]
Institut de RadioAstronomie Millimétrique [IRAM]
Gaudel, M. [Auteur]
LERMA Cergy [LERMA]
Orkisz, Jan [Auteur]
Chalmers University of Technology [Gothenburg, Sweden]
Palud, Pierre [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]
Centre de Recherche en Informatique, Signal et Automatique de Lille - UMR 9189 [CRIStAL]
Santa-Maria, Miriam [Auteur]
Instituto de Física Fundamental [Madrid] [IFF]
Magalhaes, Victor de Souza [Auteur]
Institut de RadioAstronomie Millimétrique [IRAM]
Zakardjian, Antoine [Auteur]
Institut de recherche en astrophysique et planétologie [IRAP]
Bardeau, Sebastien [Auteur]
Institut de RadioAstronomie Millimétrique [IRAM]
Bron, Emeric [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]
Chainais, Pierre [Auteur]
Centre de Recherche en Informatique, Signal et Automatique de Lille - UMR 9189 [CRIStAL]
Coudé, Simon [Auteur]
Harvard-Smithsonian Center for Astrophysics [CfA]
Worcester State University [Worcester]
Demyk, Karine [Auteur]
Institut de recherche en astrophysique et planétologie [IRAP]
Guzman Veloso, Viviana [Auteur]
Instituto de Astrofisica [Santiago]
Hughes, Annie [Auteur]
Institut de recherche en astrophysique et planétologie [IRAP]
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]
Levrier, François [Auteur]
Laboratoire de physique de l'ENS - ENS Paris [LPENS]
Lis, Dariusz [Auteur]
California Institute of Technology [CALTECH]
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]
Le Petit, Franck [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]
Peretto, Nicolas [Auteur]
Cardiff University
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]
Sievers, Albrecht [Auteur]
Institut de RadioAstronomie Millimétrique [IRAM]
Thouvenin, Pierre Antoine [Auteur]
Centre de Recherche en Informatique, Signal et Automatique de Lille - UMR 9189 [CRIStAL]

Journal title :

Astronomy and Astrophysics - A&A

Pages :

A255

Publisher :

EDP Sciences

Publication date :

2024-06

ISSN :

0004-6361

English keyword(s) :

ISM: molecules
ISM: clouds
Radiative transfer
Methods: data analysis
Methods: statistical

HAL domain(s) :

Physique [physics]/Astrophysique [astro-ph]/Astrophysique galactique [astro-ph.GA]
Statistiques [stat]/Applications [stat.AP]

English abstract : [en]

Robust radiative transfer techniques are requisite for efficiently extracting the physical and chemical information from molecular rotational lines.We study several hypotheses that enable robust estimations of the column ...
Show more >Robust radiative transfer techniques are requisite for efficiently extracting the physical and chemical information from molecular rotational lines.We study several hypotheses that enable robust estimations of the column densities and physical conditions when fitting one or two transitions per molecular species. We study the extent to which simplifying assumptions aimed at reducing the complexity of the problem introduce estimation biases and how to detect them.We focus on the CO and HCO+ isotopologues and analyze maps of a 50 square arcminutes field. We used the RADEX escape probability model to solve the statistical equilibrium equations and compute the emerging line profiles, assuming that all species coexist. Depending on the considered set of species, we also fixed the abundance ratio between some species and explored different values. We proposed a maximum likelihood estimator to infer the physical conditions and considered the effect of both the thermal noise and calibration uncertainty. We analyzed any potential biases induced by model misspecifications by comparing the results on the actual data for several sets of species and confirmed with Monte Carlo simulations. The variance of the estimations and the efficiency of the estimator were studied based on the Cramér-Rao lower bound.Column densities can be estimated with 30% accuracy, while the best estimations of the volume density are found to be within a factor of two. Under the chosen model framework, the peak 12CO(1−0) is useful for constraining the kinetic temperature. The thermal pressure is better and more robustly estimated than the volume density and kinetic temperature separately. Analyzing CO and HCO+ isotopologues and fitting the full line profile are recommended practices with respect to detecting possible biases.Combining a non-local thermodynamic equilibrium model with a rigorous analysis of the accuracy allows us to obtain an efficient estimator and identify where the model is misspecified. We note that other combinations of molecular lines could be studied in the future.Show less >

Language :

Anglais

Popular science :

Non

Collections :

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

Source :

Harvested from HAL