ALMA-IMF

X. The core population in the evolved W33-Main (G012.80) protocluster

¹ Laboratoire de Physique de l’Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 75005 Paris, France
e-mail: melanie.armante@phys.ens.fr
² Observatoire de Paris, Université PSL, Sorbonne Université, LERMA, 75014 Paris, France
³ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁴ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán 58089, Mexico
⁵ Depts. of Astronomy & Chemistry, University of Virginia, Charlottesville, VA 22904, USA
⁶ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁷ Department of Astronomy, University of Florida, PO Box 112055, USA
⁸ Université Paris Cité, Université Paris-Saclay, CEA, CNRS, AIM, 91191, Gif-sur-Yvette, France
⁹ Instituto Argentino de Radioastronomía (CCT-La Plata, CONICET; CICPBA), C.C. No. 5, 1894, Villa Elisa, Buenos Aires, Argentina
¹⁰ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile
¹¹ Department of Astronomy, Yunnan University, Kunming, 650091, PR China
¹² Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹³ Instituto Argentino de Radioastronomía (CCT-La Plata, CONICET; CICPBA), C.C. No. 5, 1894, Villa Elisa, Buenos Aires, Argentina

Received: 28 July 2023
Accepted: 19 December 2023

Abstract

Context. One of the central questions in astrophysics is the origin of the initial mass function (IMF). It is intrinsically linked to the processes from which it originates, and hence its connection with the core mass function (CMF) must be elucidated.

Aims. We aim to measure the CMF in the evolved W33-Main star-forming protocluster to compare it with CMF recently obtained in other Galactic star-forming regions, including the ones that are part of the ALMA-IMF program.

Methods. We used observations from the ALMA-IMF large programme: ~2′ × 2′ maps of emission from the continuum and selected lines at 1.3 mm and 3 mm observed by the ALMA 12m only antennas. Our angular resolution was typically 1″, that is, ~2400 au at a distance of 2.4 kpc. The lines we analysed are CO (2–1), SiO (5–4), N₂H+ (1–0), H41α as well as He41α blended with C41α. We built a census of dense cores in the region, and we measured the associated CMF based on a core-dependent temperature value.

Results. We confirmed the ‘evolved’ status of W33-Main by identifiying three H II regions within the field, and to a lesser extent based on the number and extension of N₂H⁺ filaments. We produced a filtered core catalogue of 94 candidates that we refined to take into account the contamination of the continuum by free-free and line emission, obtaining 80 cores with masses that range from 0.03 to 13.2 M_⊙. We fitted the resulting high-mass end of the CMF with a single power law of the form N(log(M)) ∝ M^α, obtaining α = −1.44_−0.22^+0.16, which is slightly steeper but consistent with the Salpeter index. We categorised our cores as prestellar and protostellar, mostly based on outflow activity and hot core nature. We found the prestellar CMF to be steeper than a Salpeter-like distribution, and the protostellar CMF to be slightly top heavy. We found a higher proportion of cores within the H II regions and their surroundings than in the rest of the field. We also found that the cores’ masses were rather low (maximum mass of ~13 M_⊙).

Conclusions. We find that star formation in W33-Main could be compatible with a ‘clump-fed’ scenario of star formation in an evolved cloud characterised by stellar feedback in the form of H II regions, and under the influence of massive stars outside the field. Our results differ from those found in less evolved young star-forming regions in the ALMA-IMF program. Further investigations are needed to elucidate the evolution of late CMFs towards the IMF over statistically significant samples.