Examinando por Autor "Chemin, Laurent"
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Ítem A machine learning approach to galactic emission-line region classification(Oxford University Press, 2023) Rhea, Carter L.; Rousseau-Nepton, Laurie; Moumen, Ismael; Prunet, Simon; Hlavacek-Larrondo, Julie; Grasha, Kathryn; Robert, Carmelle; Morisset, Christophe; Stasinska, Grazyna; Vale-Asari, Natalia; Giroux, Justine; Mcleod, Anna; Gendron-Marsolais, Marie-Lou; Wang, Junfeng; Lyman, Joe; Chemin, LaurentDiagnostic diagrams of emission-line ratios have been used e xtensiv ely to categorize extragalactic emission regions; ho we ver, these diagnostics are occasionally at odds with each other due to differing definitions. In this work, we study the applicability of supervised machine-learning techniques to systematically classify emission-line regions from the ratios of certain emission lines. Using the Million Mexican Model database, which contains information from grids of photoionization models using cloudy , and from shock models, we develop training and test sets of emission line fluxes for three key diagnostic ratios. The sets are created for three classifications: classic H II regions, planetary nebulae, and supernova remnants. We train a neural network to classify a region as one of the three classes defined abo v e giv en three ke y line ratios that are present both in the SITELLE and MUSE instruments' band-passes: [O III ] λ5007/H β, [N II ] λ6583/H α, ([S II ] λ6717 + [S II ] λ6731)/H α. We also tested the impact of the addition of the [O II ] λ3726, 3729/[O III ] λ5007 line ratio when available for the classification. A maximum luminosity limit is introduced to impro v e the classification of the planetary nebulae. Furthermore, the network is applied to SITELLE observations of a prominent field of M33. We discuss where the network succeeds and why it fails in certain cases. Our results provide a framework for the use of machine learning as a tool for the classification of extragalactic emission regions. Further work is needed to build more comprehensive training sets and adapt the method to additional observational constraints. © 2023 The Author(s).Ítem Constraining the LyC escape fraction from LEGUS star clusters with SIGNALS H ii region observations: a pilot study of NGC 628(Oxford University Press, 2023-09-01) Teh, Jia Wei; Grasha, Kathryn; Krumholz, Mark R; Battisti, Andrew J; Calzetti, Daniela; Rousseau-Nepton, Laurie; Rhea, Carter; Adamo, Angela; Kennicutt, Robert C; Grebel, Eva K; Cook, David O; Combes, Francoise; Messa, Mateo; Linden, Sean T.; Klessen, Ralf S; Vilchez, Jos M; Fumagalli, Michele; Mcleod, Anna; Smith, Linda J; Chemin, Laurent; Wang, Junfeng; Sabbi, Elena; Sacchi, Elena; Petric, Andreea; Bruna, Lorenza Della; Boselli, AlessandroThe ionizing radiation of young and massive stars is a crucial form of stellar feedback. Most ionizing (Lyman-continuum; LyC, λ < 912Å) photons are absorbed close to the stars that produce them, forming compact H ii regions, but some escape into the wider galaxy. Quantifying the fraction of LyC photons that escape is an open problem. In this work, we present a seminovel method to estimate the escape fraction by combining broadband photometry of star clusters from the Legacy ExtraGalactic UV Survey (LEGUS) with H ii regions observed by the Star formation, Ionized gas, and Nebular Abundances Legacy Survey (SIGNALS) in the nearby spiral galaxy NGC 628. We first assess the completeness of the combined catalogue, and find that 49 per cent of H ii regions lack corresponding star clusters as a result of a difference in the sensitivities of the LEGUS and SIGNALS surveys. For H ii regions that do have matching clusters, we infer the escape fraction from the difference between the ionizing power required to produce the observed H ii luminosity and the predicted ionizing photon output of their host star clusters; the latter is computed using a combination of LEGUS photometric observations and a stochastic stellar population synthesis code slug (Stochastically Lighting Up Galaxies). Overall, we find an escape fraction of across our sample of 42 H ii regions; in particular, we find H ii regions with high fesc are predominantly regions with low -luminosity. We also report possible correlation between fesc and the emission lines and. © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Ítem Detection of the Keplerian decline in the Milky Way rotation curve(EDP Sciences, 2023-10-01) Jiao, Yongjun; Hammer, François; Wang, Haifeng; Amram, Philippe; Chemin, Laurent; Yang, YanbinOur position inside the Galactic disc has previously prevented us from establishing an accurate rotation curve (RC). The advent of Gaia and its third data release (Gaia DR3) made it possible to specify the RC up to twice the optical radius. We aim to establish a new RC of the Galaxy from the Gaia DR3 by drastically reducing systematic uncertainties. Our goal is to provide a new estimate of the mass of the Galaxy. We compared different estimates, established a robust assessment of the systematic uncertainties, and addressed differences in methodologies, particularly regarding distance estimates. We find a sharply decreasing RC for the Milky Way; the decrease in velocity between 19.5 and 26.5 kpc is approximately 30 km s-1. We identify, for the first time, a Keplerian decline of the RC, starting at ∼19 kpc and ending at ∼26.5 kpc from the Galaxy centre, while a flat RC is rejected with a significance of 3σ. The total mass is revised downwards to 2.06-0.13+0.24× 1011 M⊙, which is in agreement with the absence of a significant mass increase at radii larger than 19 kpc. We evaluated the upper limit on the total mass by considering the upper values of velocity measurements, which leads to a strict, unsurpassable limit of 5.4× 1011 M⊙Ítem Looking at the Distant Universe with the MeerKAT Array: The H i Mass Function in the Local Universe(Institute of Physics, 2025-03) Kazemi-Moridani, Amir; Baker, Andrew J.; Verheijen, Marc; Gawiser, Eric; Blyth, Sarah-Louise; Obreschkow, Danail; Chemin, Laurent; Collier, Jordan D.; Cook, Kyle W.; Delhaize, Jacinta; Elson, Ed; Frank, Bradley S.; Glowacki, Marcin; Hess, Kelley M.; Holwerda, Benne W.; Hutchens, Zackary L.; Jarvis, Matt J.; Kaasinen, Melanie; Makhathini, Sphesihle; Mohapatra, Abhisek; Pan, Hengxing; Schröder, Anja C.; Stockenstroom, Leyya; Vaccari, Mattia; Westmeier, Tobias; Wu, John F.; Zwaan, MartinWe present measurements of the neutral atomic hydrogen (H i) mass function (HiMF) and cosmic H i density (ΩH I) at 0 ≤ z ≤ 0.088 from the Looking at the Distant Universe with MeerKAT Array (LADUMA) survey. Using LADUMA Data Release 1 (DR1), we analyze the HiMF via a new “recovery matrix” method that we benchmark against a more traditional modified maximum likelihood (MML) method. Our analysis, which implements a forward modeling approach, corrects for survey incompleteness and uses extensive synthetic source injections to ensure robust estimates of the HiMF parameters and their associated uncertainties. This new method tracks the recovery of sources in mass bins different from those in which they were injected and incorporates a Poisson likelihood in the forward modeling process, allowing it to correctly handle uncertainties in bins with few or no detections. The application of our analysis to a high-purity subsample of the LADUMA DR1 spectral line catalog in turn mitigates any possible biases that could result from the inconsistent treatment of synthetic and real sources. For the surveyed redshift range, the recovered Schechter function normalization, low-mass slope, and “knee” mass are ϕ * = 3.5 6 − 1.92 + 0.97 × 1 0 − 3 Mpc−3 dex−1, α = − 1.1 8 − 0.19 + 0.08 , and log ( M * / M ⊙ ) = 10.0 1 − 0.12 + 0.31 , respectively, which together imply a comoving cosmic H i density of Ω H I = 3.0 9 − 0.47 + 0.65 × 1 0 − 4 . Our results show consistency between recovery matrix and MML methods and with previous low-redshift studies, giving confidence that the cosmic volume probed by LADUMA, even at low redshifts, is not an outlier in terms of its H i content. © 2025. The Author(s). Published by the American Astronomical Society.Ítem Looking at the Distant Universe with the MeerKAT Array: The H i Mass Function in the Local Universe(Institute of Physics, 0025-03) Kazemi-Moridani, Amir; Baker, Andrew J.; Verheijen, Marc; Gawiser, Eric; Blyth, Sarah-Louise; Obreschkow, Danail; Chemin, Laurent; Collier, Jordan D.; Cook, Kyle W; Delhaize, Jacinta; Elson, Ed; Frank, Bradley S.We present measurements of the neutral atomic hydrogen (H i) mass function (HiMF) and cosmic H i density (ΩH I) at 0 ≤ z ≤ 0.088 from the Looking at the Distant Universe with MeerKAT Array (LADUMA) survey. Using LADUMA Data Release 1 (DR1), we analyze the HiMF via a new “recovery matrix” method that we benchmark against a more traditional modified maximum likelihood (MML) method. Our analysis, which implements a forward modeling approach, corrects for survey incompleteness and uses extensive synthetic source injections to ensure robust estimates of the HiMF parameters and their associated uncertainties. This new method tracks the recovery of sources in mass bins different from those in which they were injected and incorporates a Poisson likelihood in the forward modeling process, allowing it to correctly handle uncertainties in bins with few or no detections. The application of our analysis to a high-purity subsample of the LADUMA DR1 spectral line catalog in turn mitigates any possible biases that could result from the inconsistent treatment of synthetic and real sources. For the surveyed redshift range, the recovered Schechter function normalization, low-mass slope, and “knee” mass are ϕ * = 3.5 6 − 1.92 + 0.97 × 1 0 − 3 Mpc−3 dex−1, α = − 1.1 8 − 0.19 + 0.08 , and log ( M * / M ⊙ ) = 10.0 1 − 0.12 + 0.31 , respectively, which together imply a comoving cosmic H i density of Ω H I = 3.0 9 − 0.47 + 0.65 × 1 0 − 4 . Our results show consistency between recovery matrix and MML methods and with previous low-redshift studies, giving confidence that the cosmic volume probed by LADUMA, even at low redshifts, is not an outlier in terms of its H i content. © 2025. The Author(s). Published by the American Astronomical Society.