NIR Subarcsec Images of W49A: Uncovering the Beast

Joao Alves, Nicole Homeier

Publications: Contribution to bookContribution to proceedings


We present subarcsecond J H and Ks images (FWHM ˜ 0.5'') of an unbiased 5'×5' (16 pc × 16 pc) survey of the densest region of the W49 giant molecular cloud. The observations reveal 4 massive stellar clusters (with stars as massive as ˜ 120 M⊙) the larger (Cluster 1) about 3 pc East of the well known Welch ring of ultra-compact HII regions. Cluster 1 is a) extincted by at least AV > 20 mag of foreground (unrelated and local) extinction b) has more than 30 magnitudes of internal inhomogeneous extinction implying that it is still deeply buried in its parental molecular cloud and c) is powering a 6 pc diameter giant HII region seen both at the NIR and radio continuum. We also identify the exciting sources of several UC HII 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 multi-seeded instead of resulting from a coherent trigger
Original languageEnglish
Title of host publicationStar Formation at High Angular Resolution, International Astronomical Union
Subtitle of host publicationSymposium no. 221, held 22-25 July, 2003 in Sydney, Australia, Poster meeting abstract
Publication statusPublished - 2004

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