Uncovering the Beast: Discovery of Embedded Massive Stellar Clusters in W49A

J. Alves, N. Homeier

Publications: Contribution to journalArticlePeer Reviewed


We present subarcsecond J, H, and Ks images (FWHM~0.5") of an unbiased 5'×5' (16×16 pc) survey of the densest region of the W49 giant molecular cloud. The observations reveal four massive stellar clusters (with stars as massive as ~120 Msolar), the largest (cluster 1) about 3 pc east of the well-known Welch ring of ultracompact H II regions. Cluster 1 is (i) extincted by at least AV>20 mag of foreground (unrelated and local) extinction, (ii) has more than 30 mag of internal inhomogeneous extinction, implying that it is still deeply buried in its parental molecular cloud, and (iii) is powering a 6 pc diameter giant H II region seen at both the near-infrared and the radio continuum. We also identify the exciting sources of several ultracompact H II regions. The census of massive stars in W49A agrees or is slightly overabundant when compared with the number of Lyman continuum photons derived from radio observations. We argue that although the formation of the Welch ring could have been triggered by cluster 1, the entire W49A starburst region seems to have been multiseeded instead of resulting from a coherent trigger. Based on observations collected at the European Southern Observatory, La Silla, Chile.
Original languageEnglish
Pages (from-to)L45-L49
JournalThe Astrophysical journal Letters
Issue number1
Publication statusPublished - 1 May 2003


  • ISM: H II Regions
  • ISM: Individual: Alphanumeric: W49A
  • Galaxy: Open Clusters and Associations: Individual: Alphanumeric: W49A
  • Stars: Formation

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