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

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dc.contributor.authorRoueff, Antoine
dc.contributor.authorPety, Jerome
dc.contributor.authorGerin, Maryvonne
dc.contributor.authorSegal, Leontine E.
dc.contributor.authorGoicoechea, Javier R.
dc.contributor.authorLiszt, Harvey S.
dc.contributor.authorGratier, Pierre
dc.contributor.authorBeslic, Ivana
dc.contributor.authorEinig, Lucas
dc.contributor.authorGaudel, Mathilde
dc.contributor.authorOrkisz, Jan H.
dc.contributor.authorPalud, Pierre
dc.contributor.authorSanta-Maria, Miriam G.
dc.contributor.authorMagalhaes, Victor de Souza
dc.contributor.authorZakardjian, Antoine
dc.contributor.authorBardeau, Sebastien
dc.contributor.authorBron, Emeric
dc.contributor.authorChainais, Pierre
dc.contributor.authorCoude, Simon
dc.contributor.authorDemyk, Karine
dc.contributor.authorGuzman, Viviana V.
dc.contributor.authorHughes, Annie
dc.contributor.authorLanguignon, David
dc.contributor.authorLevrier, Francois
dc.contributor.authorLis, Dariusz C.
dc.contributor.authorLe Bourlot, Jacques
dc.contributor.authorLe Petit, Franck
dc.contributor.authorPeretto, Nicolas
dc.contributor.authorRoueff, Evelyne
dc.contributor.authorSievers, Albrecht
dc.contributor.authorThouvenin, Pierre-Antoine
dc.date.accessioned2025-01-20T16:15:03Z
dc.date.available2025-01-20T16:15:03Z
dc.date.issued2024
dc.description.abstractContext. Robust radiative transfer techniques are requisite for efficiently extracting the physical and chemical information from molecular rotational lines. Aims. 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. Methods. 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 Cramer-Rao lower bound. Results. 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 (CO)-C-12 (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. Conclusions. 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.
dc.fuente.origenWOS
dc.identifier.doi10.1051/0004-6361/202449148
dc.identifier.eissn1432-0746
dc.identifier.issn0004-6361
dc.identifier.urihttps://doi.org/10.1051/0004-6361/202449148
dc.identifier.urihttps://repositorio.uc.cl/handle/11534/90474
dc.identifier.wosidWOS:001252009900010
dc.language.isoen
dc.revistaAstronomy & astrophysics
dc.rightsacceso restringido
dc.subjectline: profiles
dc.subjectradiative transfer
dc.subjectmethods: data analysis
dc.subjectmethods: statistical
dc.subjectISM: clouds
dc.subjectISM: general
dc.titleBias 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
dc.typeartículo
dc.volumen686
sipa.indexWOS
sipa.trazabilidadWOS;2025-01-12
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