Probing the formation of intermediate- to high-mass stars in protoclusters - A detailed millimeter study of the NGC 2264 clumps

By Nicolas Peretto, P. André, Arnaud Belloche. 2005

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We present the results of dust continuum and molecular line observations of two massive cluster-forming clumps, NGC 2264-C and NGC 2264-D, including extensive mapping performed with the MAMBO bolometer array and the HERA heterodyne array on the IRAM 30 m telescope. Both NGC 2264 clumps are located in the Mon OB1 giant molecular cloud complex, adjacent to one another. Twelve and fifteen compact millimeter continuum sources (i.e. MMSs) were identified in clumps C and D, respectively. These MMSs have larger sizes and masses than the millimeter continuum condensations detected in well-known nearby protoclusters such as $\rho$ Ophiuchi. The MMSs of NGC 2264 are closer in size to the DCO+ "cores" of $\rho$ Oph, although they are somewhat denser and exhibit broader linewidths. Most of the MMSs of NGC 2264-C harbor candidate Class 0 protostars associated with shocked molecular hydrogen jets. Evidence of widespread infall motions was found in, e.g., HCO+(3-2) or CS(3-2) in both NGC 2264-C and NGC 2264-D. A sharp velocity discontinuity ~2 km s-1 in amplitude was observed in N2H+(1-0) and H13CO+(1-0) in the central, innermost part of NGC 2264-C, which we interpreted as the signature of a strong dynamical interaction between two MMSs and their possible merging with the central MMS C-MM3. Radiative transfer modelling supports the idea that NGC 2264-C is a highly unstable prolate clump in the process of collapsing along its long axis on a near free-fall dynamical timescale ~ $1.7 \times 10 ^5$ yr. Our model fit of this large-scale collapse suggests a maximum mass inflow rate ~ $3\times 10^{-3}~M_{\odot}$ yr-1 toward the central protostellar object C-MM3. In NGC 2264-D, we estimated a mass infall rate $\dot{M}_{\rm DMM1} \sim 1.1 \times 10 ^{-4}~M_{\odot}$ yr-1 toward the rotating Class 0 object D-MM1, also based on radiative transfer modelling of the observations. Such infall rates are sufficiently high to overcome radiation pressure and allow the formation of ~ $20~M_{\odot}$ stars by accretion in ~ $1.7 \times 10 ^5$ yr, i.e., a time that is similar to the global dynamical timescale of the central part of NGC 2264-C. We conclude that we are likely witnessing the formation of a high-mass ($\ga$ $10~M_{\odot}$) protostar in the central part of NGC 2264-C. Our results suggest a picture of massive star formation intermediate between the scenario of stellar mergers of Bonnell et al. (1998) and the massive turbulent core model of McKee & Tan (2003), whereby a turbulent, massive ultra-dense core is formed by the gravitational merger of two or more Class 0 protostellar cores at the center of a collapsing protocluster.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/6376e0d719f58dcf2fc1c4b039aa27feef1d3279

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Citations in the corpus

Global collapse of molecular clouds as a formation mechanism for the most massive stars (2013, background): “However, there are several sources now for which large-scale infall has been suggested to play a major role in building up the mass of star-forming cores (e.g. Peretto et al. 2006; Schneider et al. 2010; Barnes et al. 2010; GalvánMadrid et al. 2010; Liu et al. 2012).”
RADIATION-HYDRODYNAMIC SIMULATIONS OF THE FORMATION OF ORION-LIKE STAR CLUSTERS. II. THE INITIAL MASS FUNCTION FROM WINDS, TURBULENCE, AND RADIATION (2012, background): “A number of authors have also proposed hybrid models, in which massive stars form from gravitationally bound gas structures, but these structures are assembled and fed from larger scales at the same time as they form massive stars (Peretto et al. 2006; Wang et al. 2010).”
The initial conditions of stellar protocluster formation - I. A catalogue of Spitzer dark clouds (2009, background): “So far, the study of the earliest stages of the formation of protoclusters have mostly focussed on the closest objects such asρ-Oph(e.g. Motte et al. 1998; André et al. 2007), Perseus (Hatchell et al. 2005; Enoch et al. 2006), NGC2264 (e.g. Peretto et al. 2006; Teixeira et al. 2006).”
Protostellar Turbulence Driven by Collimated Outflows (2007, background): “…infall and outflow are observed in a number of embedded clusters, including NGC 1333 (Walsh et al. 2006; Knee & Sandell 2000), the Serpens cloud core (Williams & Myers 2000; Olmi & Testi 2002; Davis et al. 1999), and NGC 2264 (Peretto et al. 2006; Williams & Garland 2002; Wolf-Chase et al. 2003).”
The ATLASGAL survey: a catalog of dust condensations in the Galactic plane (2013, methodology): “It has also been applied for smaller regions, such as RCW 106 (Mookerjea et al. 2004), NGC 2264 (Peretto et al. 2006) and G327.”
The initial conditions of star formation in the Ophiuchus main cloud: Kinematics of the protocluster condensations , (2007, background): “C clusterforming clump in the Mon OB1 complex, Peretto et al. (2006) found direct evidence of a strong dynamical interaction in the dense inner region of that protocluster.”
Dynamic star formation in the massive DR21 filament (2010, background): “The [HCO+]/[H2] abundance in high-mass star-forming regions is typically quoted to be 1.5–2.5 × 10−9 (Peretto et al. 2006, Marseille et al. 2008).”
The spine of the swan: a Herschel study of the DR21 ridge and filaments in Cygnus X (2012, unknown): “C (Peretto et al. 2006).”
The Birth Environment of the Solar System (2010, background): “Observations of young embedded clusters are starting to provide clues to the expected values of β. Growing observational evidence suggests that forming stars in clusters are not born with virial velocities (Walsh et al. 2004, Peretto et al. 2006).”
Cluster Formation in Protostellar Outflow-driven Turbulence (2005, background): “The majority do not show clear evidence of free-fall collapse (Garay 2005; see, however, Wu & Evans 2003 and Peretto et al. 2006 for examples of rapid infall), indicating quick replenishment of decayed turbulence, most likely by outflows.”
Early Evolution of Stellar Groups and Clusters: Environmental Effects on Forming Planetary Systems (2005, background): “As another example, the clumpto-clump velocities in the NGC 2264 region are estimated to be about 3 times smaller than that expected in virial equilibrium (Peretto et al. 2006).”
DYNAMICAL MASS SEGREGATION ON A VERY SHORT TIMESCALE (2009, background): “Prestellar cores are often observed to move subsonically (Belloche et al. 2001; André 2002; Walsh et al. 2004; Peretto et al. 2006; Kirk et al. 2007).”