Core to ultracompact HII region evolution in the W49A massive protocluster

• Published in: Astronomy and astrophysics (Berlin) 2024-07, Vol.687, p.A84
• Main Authors: Nony, T., Galván-Madrid, R., Brouillet, N., Suárez, G., Louvet, F., De Pree, C. G., Juárez-Gama, M., Ginsburg, A., Immer, K., Lin, Y., Liu, H. B., Román-Zúñiga, C. G., Zhang, Q.
• Format: Article
• Language: English
• Subjects: Angular resolution; Emission; Evolution; Methyl formate; Protostars
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202449279

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 H II (H/UC H II ) regions was established from the analysis of VLA 3.3 cm continuum and H30 α line 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 H II region and 19 HMCs over the ALMA mosaic. The 52 cores with an H/UC H II region 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 H30 α . 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 H II regions as a reference, we found the statistical lifetimes of the HMC and massive protostellar phases in W49N to be about 6 × 10 4 yr and 1.4 × 10 5 yr, respectively. We also showed that HMCs can coexist with H/UC H II regions during a short fraction of the core lifetime, about 2 × 10 4 yr. This indicates a rapid dispersal of the inner molecule envelope once the HC H II is formed.