Discovery of Large-Scale Gravitational Infall in a Possible Massive Protostellar Cluster

We report Mopra (ATNF), Anglo-Australian Telescope, and Atacama Submillimeter Telescope Experiment observations of a molecular core in Carina, BY72 = G286.21+0.17, which give evidence of large-scale gravitational infall in the dense gas. From the millimetre and far-infrared data, the core has mass ∼ 5,000 M⊙, luminosity ∼ 2–3×10 L⊙, diameter ∼ 0.9 pc, and mass infall rate ∼ 2.4×10 −2 M⊙yr . If confirmed, this rate for gravitational infall in a molecular core may be the highest yet seen. The near-infrared K-band imaging shows an adjacent compact HII region and IR cluster surrounded by a shell-like photodissociation region showing H2 emission. At the molecular infall peak, the K imaging also reveals a deeply embedded group of stars with associated H2 emission. The combination of these features is very unusual and we suggest they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation. Subject headings: astrochemistry — infrared: ISM — ISM: kinematics and dynamics — ISM: molecules — radio lines: ISM — stars:formation School of Physics A28, University of Sydney, NSW 2006, Australia Astronomy Department, University of Florida, Gainesville, FL 32611, USA Department of Physical Science, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan Anglo-Australian Observatory, PO Box 296, Epping, NSW 1710, Australia Department of Astrophysics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan