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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 HIIregions 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 13.2M⊙. We fitted the resulting high-mass end of the CMF with a single power law of the form N(log(M)) ∝ Mα, obtainingα= −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 HIIregions and their surroundings than in the rest of the field. We also found that the cores’ masses were rather low (maximum mass of ~13M⊙). 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 HIIregions, 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.
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This content will become publicly available on July 1, 2025
Core to ultracompact HII region evolution in the W49A massive protocluster
Aims.We aim to identify and characterize cores in the high-mass protocluster W49A, determine their evolutionary stages, and measure the associated lifetimes. Methods.We built a catalog of 129 cores extracted from an ALMA 1.3 mm continuum image at 0.26″ (2900 au) angular resolution. The association between cores and hypercompact or ultracompact HII(H/UC HII) regions was established from the analysis of VLA 3.3 cm continuum and H30αline observations. We also looked for emission of hot molecular cores (HMCs) using the methyl formate doublet at 218.29 GHz. Results.We identified 40 cores associated with an H/UC HIIregion and 19 HMCs over the ALMA mosaic. The 52 cores with an H/UC HIIregion and/or an HMC are assumed to be high-mass protostellar cores, while the rest of the core population likely consists of prestellar cores and low-mass protostellar cores. We found a good agreement between the two tracers of ionized gas, with 23 common detections and only four cores detected at 3.3 cm and not in H30α. The spectral indexes from 3.3 cm to 1.3 mm range from 1, for the youngest cores with partially optically thick free-free emission, to about −0.1, which is for the optically thin free-free emission obtained for cores that are likely more evolved. Conclusions.Using the H/UC HIIregions as a reference, we found the statistical lifetimes of the HMC and massive protostellar phases in W49N to be about 6 × 104yr and 1.4 × 105yr, respectively. We also showed that HMCs can coexist with H/UC HIIregions during a short fraction of the core lifetime, about 2 × 104yr. This indicates a rapid dispersal of the inner molecule envelope once the HC HIIis formed.
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- Award ID(s):
- 2142300
- PAR ID:
- 10569720
- Publisher / Repository:
- Astronomy and Astrophysics
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 687
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A84
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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