ALMA-IMF

IV. A comparative study of the main hot cores in W43-MM1: Detection, temperature, and molecular composition

¹ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
e-mail: nathalie.brouillet@u-bordeaux.fr
² Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán 58089, Mexico
³ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁴ Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France
⁵ Observatoire de Paris, PSL University, Sorbonne Université, LERMA, 75014 Paris, France
⁶ DAS, Universidad de Chile, 1515 camino el Observatorio, las Condes, Santiago, Chile
⁷ Department of Astronomy, University of Florida, PO Box 112055, USA
⁸ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁹ Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona, c/ Martí i Franquès 1, 08028 Barcelona, Spain
¹⁰ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), c/ Martí i Franquès 1, 08028 Barcelona, Spain
¹¹ Institut d’Estudis Espacials de Catalunya (IEEC), c. Gran Capità, 2-4, 08034 Barcelona, Spain
¹² Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹³ Instituto Argentino de Radioastronomía (CCT-La Plata, CONICET; CICPBA), C.C. No. 5, 1894, Villa Elisa, Buenos Aires, Argentina
¹⁴ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁵ Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁶ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, 4030000 Concepción, Chile

Received: 29 March 2022
Accepted: 27 June 2022

Abstract

Context. Hot cores are signposts of the protostellar activity of dense cores in star-forming regions. W43-MM1 is a young region that is very rich in terms of high-mass star formation, which is highlighted by the presence of large numbers of high-mass cores and outflows.

Aims. We aim to systematically identify the massive cores in W43-MM1 that contain a hot core and compare their molecular composition.

Methods. We used Atacama Large Millimeter/sub-millimeter Array (ALMA) high-spatial resolution (~2500 au) data to identify line-rich protostellar cores and carried out a comparative study of their temperature and molecular composition. Here, the identification of hot cores is based on both the spatial distribution of the complex organic molecules and the contribution of molecular lines relative to the continuum intensity. We rely on the analysis of CH₃CN and CH₃CCH to estimate the temperatures of the selected cores. Finally, we rescale the spectra of the different hot cores based on their CH₃OCHO line intensities to directly compare the detections and line intensities of the other species.

Results. W43-MM1 turns out to be a region that is rich in massive hot cores. It contains at least one less massive (core #11, 2 M_⊙) and seven massive (16−100 M_⊙) hot cores. The excitation temperature of CH₃CN, whose emission is centred on the cores, is of the same order for all of them (120–160 K). There is a factor of up to 30 difference in the intensity of the lines of complex organic molecules (COMs). However the molecular emission of the hot cores appears to be the same or within a factor of 2–3. This suggests that these massive cores, which span about an order of magnitude in core mass, have a similar chemical composition and show similar excitation of most of the COMs. In contrast, CH₃CCH emission is found to preferentially trace the envelope, with a temperature ranging from 50 K to 90 K. Lines in core #11 are less optically thick, which makes them proportionally more intense compared to the continuum than lines observed in the more massive hot cores. Core #1, the most massive hot core of W43-MM1, shows a richer line spectrum than the other cores in our sample, in particular in N-bearing molecules and ethylene glycol lines. In core #2, the emission of O-bearing molecules, such as OCS, CH₃OCHO, and CH₃OH, does not peak at the dust continuum core centre; the blueshifted and redshifted emission corresponds to the outflow lobes, suggesting formation via sublimation of the ice mantles through shocks or UV irradiation on the walls of the cavity. These data establish a benchmark for the study of other massive star-formation regions and hot cores.