Discovery of large-scale gravitational infall in a massive protostellar cluster

Abstract

We report Mopra Australia Telescope National Facility (ATNF), Anglo‐Australian Telescope and Atacama Submillimeter Telescope Experiment observations of a molecular clump in Carina, BYF73 = G286.21+0.17, which give evidence of large‐scale gravitational infall in the dense gas. From the millimetre and far‐infrared data, the clump has a mass of ∼2 × 104 M⊙, luminosity of ∼2–3 × 104 L⊙ and diameter of ∼0.9 pc. From radiative transfer modelling, we derive a mass infall rate of ∼3.4 × 10−2 M⊙ yr−1. If confirmed, this rate for gravitational infall in a molecular core or clump may be the highest yet seen. The near‐infrared K‐band imaging shows an adjacent compact H ii 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 that they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation.

The Stellar Content of the Infalling Molecular Clump G286.21+0.17

“…To the north-west of G286.21+0.17 is located more exposed star formation as noted in Barnes et al (2010). The strong diffuse emission in a shell-like structure suggests there to be an HII region present, which is confirmed by the Br γ emission seen by Barnes et al (2010).…”

“…Fig. 1 shows the near-infrared observations together with the H 13 CO + (1 − 0) contours obtained from the observations discussed in Barnes et al (2010). The clump G286.21+0.17 is seen as the molecular emission peak at the middle of the image.…”

“…The clump G286.21+0.17 is seen as the molecular emission peak at the middle of the image. Barnes et al (2010); Ohlendorf et al (2013) noted the presence of embedded sources within the clump but it is only with the sensitivity and spatial resolution in the near-infrared that the relative richness of the cluster is evident. Most of the sources are heavily obscured and only detected in the Ks band.…”

“…One of the first discoveries out of the survey was the identification of a massive clump with a very large infall (Barnes et al 2010). The massive clump G286.21+0.17 is located in the Carina star forming complex and was identified to have a molecular infall rate of (3.4 × 10 −2 M yr −1 ), indicating that star formation is still ongoing (Barnes et al 2010, where the core is known as BYF73). They suggested a molecular mass of up to 2×10 4 M assuming a distance of 2.5 kpc and a luminosity of 2-3×10 4 L (see also Verma et al 1994).…”

“…The CHaMP survey (Barnes et al 2005) is as unbiased survey of 20 × 3 degrees of the Galactic plane to characterize the star formation (see also Barnes et al 2011). One of the first discoveries out of the survey was the identification of a massive clump with a very large infall (Barnes et al 2010). The massive clump G286.21+0.17 is located in the Carina star forming complex and was identified to have a molecular infall rate of (3.4 × 10 −2 M yr −1 ), indicating that star formation is still ongoing (Barnes et al 2010, where the core is known as BYF73).…”