The Zero-Age Massive Stellar Population of W49A from VLA Observations

Abstract

We use all-configuration VLA data at 3.3 cm with a physical resolution of ~2000 AU to infer the embedded zero-age massive stellar population of the W49A protocluster, as traced by its compact, ultracompact (UC), and hypercompact (HC) H II regions. Our method consists of visual source identification, the derivation of stellar ionizing-photon rates from the observed emission measure, and the further derivation of stellar masses and luminosities using state-of-the-art stellar calibrations. Considering the 101 robust detections, maximum-likelihood estimation fitting of the high-mass end (M > 10.9 M_\odot) of the sample yields power-law slopes Gamma >= 2.40 for the logarithmic representation of the stellar initial mass function (IMF): dN/d(log M) proportional to M^{-Gamma}. The result is robust considering different assumptions for the ionizing stellar systems. The slopes remain at Gamma >= 1.88 after correction for optical depth effects at 3.3 cm. Therefore, the inferred distribution of stellar masses presents a clear deficit in the high-mass end as compared to the standard stellar IMF (Gamma = 1.35). We propose that this is due to a shorter lifetime of the radio-detected H II regions produced by higher-mass stars, but evolutionary effects in the mass distribution of star formation within embedded protoclusters cannot be discarded.

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BibTeX RIS

BibTeX

@misc{juarezgama2026zeroage,
  title = {{The Zero-Age Massive Stellar Population of W49A from VLA Observations}},
  author = {M. Juárez-Gama and R. Galván-Madrid and G. Suárez and C. G. De Pree and J. J. Tobin and G. Bruzual and A. Ginsburg and J. E. Mendoza-Torres and H. B. Liu and D. Wilner and T. Nony and A. Parra-López and R. Rivera-Soto and A. F. McLeod and N. Cunningham and X. Lu and E. F. Jiménez-Andrade},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2608.05453},
  eprint = {2608.05453},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2608.05453},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - The Zero-Age Massive Stellar Population of W49A from VLA Observations
AU  - M. Juárez-Gama
AU  - R. Galván-Madrid
AU  - G. Suárez
AU  - C. G. De Pree
AU  - J. J. Tobin
AU  - G. Bruzual
AU  - A. Ginsburg
AU  - J. E. Mendoza-Torres
AU  - H. B. Liu
AU  - D. Wilner
AU  - T. Nony
AU  - A. Parra-López
AU  - R. Rivera-Soto
AU  - A. F. McLeod
AU  - N. Cunningham
AU  - X. Lu
AU  - E. F. Jiménez-Andrade
PY  - 2026
DA  - 2026/09/02
PB  - arXiv
DO  - 10.48550/arxiv.2608.05453
UR  - https://arxiv.org/abs/2608.05453
AB  - We use all-configuration VLA data at 3.3 cm with a physical resolution of ~2000 AU to infer the embedded zero-age massive stellar population of the W49A protocluster, as traced by its compact, ultracompact (UC), and hypercompact (HC) H II regions. Our method consists of visual source identification, the derivation of stellar ionizing-photon rates from the observed emission measure, and the further derivation of stellar masses and luminosities using state-of-the-art stellar calibrations. Considering the 101 robust detections, maximum-likelihood estimation fitting of the high-mass end (M > 10.9 M_\odot) of the sample yields power-law slopes Gamma >= 2.40 for the logarithmic representation of the stellar initial mass function (IMF): dN/d(log M) proportional to M^{-Gamma}. The result is robust considering different assumptions for the ionizing stellar systems. The slopes remain at Gamma >= 1.88 after correction for optical depth effects at 3.3 cm. Therefore, the inferred distribution of stellar masses presents a clear deficit in the high-mass end as compared to the standard stellar IMF (Gamma = 1.35). We propose that this is due to a shorter lifetime of the radio-detected H II regions produced by higher-mass stars, but evolutionary effects in the mass distribution of star formation within embedded protoclusters cannot be discarded.
ER  -

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