Probing the formation of intermediate- to high-mass stars in protoclusters

Abstract

Aims. The earliest phases of massive star formation in clusters are still poorly understood. Here, we test the hypothesis for high-mass star formation proposed in our earlier paper (Peretto et al. 2006) stating that a massive, ultra-dense core may be currently forming at the center of the collapsing NGC 2264-C protocluster via the gravitational coalescence of several intermediate-mass Class 0 objects. Methods. In order to confirm the physical validity of this hypothesis, we carried out IRAM Plateau de Bure interferometer observations of NGC 2264-C and performed SPH numerical simulations of the collapse of a Jeans-unstable, prolate dense clump. A detailed comparison between these hydrodynamic simulations and both our earlier IRAM 30 m observations and the new interferometer observations is presented. Results. Our Plateau de Bure observations provide evidence for disk emission in three of the six Class 0-like objects identified earlier with the 30 m in the NGC 2264-C clump. Furthermore, they reveal the presence of a new compact source (C-MM13) located only ∼10 000 AU away, but separated by ∼1.1 km s −1 in (projected) velocity, from the most massive Class 0 object (C-MM3) lying at the very center of NGC 2264-C. Detailed comparison with our numerical SPH simulations supports the view that NGC 2264-C is an elongated cluster-forming clump in the process of collapsing and fragmenting along its long axis, leading to a strong dynamical interaction and possible protostar merger in the central region of the clump. The marked velocity difference observed between the two central objects C-MM3 and C-MM13, which can be reproduced in the simulations, is interpreted as an observational signature of this dynamical interaction. The present study also sets several quantitative constraints on the initial conditions of large-scale collapse in NGC 2264-C. Our hydrodynamic simulations indicate that the observed velocity pattern characterizes an early phase of protocluster collapse which survives for an only short period of time (i.e., ≤1 × 10 5 yr). To provide a good match to the observations the simulations require an initial ratio of turbulent to gravitational energy of only ∼5%, which strongly suggests that the NGC 2264-C clump is structured primarily by gravity rather than turbulence. The required "cold" initial conditions may result from rapid compression by an external trigger. Conclusions. We speculate that NGC 2264-C is not an isolated case but may point to key features of the initial phases of high-mass star formation in protoclusters.

Probing the role of protostellar feedback in clustered star formation

“…The internal structure of NGC 2264-C and NGC 2264-D was subsequently resolved by higher-resolution millimeter and submillimeter studies Williams & Garland 2002;Peretto et al 2006Peretto et al , 2007. In particular, through 1.2 mm continuum observations, Peretto et al (2006) identified 12 compact dense cores in NGC 2264-C (see Fig.…”

“…The IRAM Plateau de Bure interferometer observations of Peretto et al (2007) revealed a thirteenth source, C-MM13, located only 13.5 (or ∼0.05 pc) away from C-MM3.…”

“…In their study, Peretto et al (2007) successfully modeled the dynamical evolution of the NGC 2264-C protocluster. They compared the available millimeter observations with SPH numerical simulations of the collapse of a Jeans-unstable, prolate dense clump.…”

“…However, the total mass of dense gas (i.e., with n H 2 > 10 4 cm −3 ) was ∼10 times lower in the best-fit simulations than in the actual NGC 2264-C clump. When Peretto et al (2007) increased the mass of dense gas by a factor of 10 in their numerical simulations, a larger number of cores was generated, leading to a poor match to the observations. It seemed therefore that an additional source of support against gravity, not included in the simulations of Peretto et al (2007), had to be invoked to explain the current dynamical state NGC 2264-C. Peretto et al suggested that this extra support could arise from protostellar feedback and/or magnetic fields.…”

“…The eleven outflows discovered in the present survey are labeled by F1 to F11. The background greyscale image is the 1.2 mm dust continuum map obtained by Peretto et al (2006) with MAMBO on the IRAM-30 m. White crosses and numbers refer to the millimeter continuum peaks identified by Peretto et al (2006Peretto et al ( , 2007 (see also Fig. 1).…”