Fragmentation and mass segregation in the massive dense cores of Cygnus X

By S. Bontemps, Fr'ed'erique Motte, T. Csengeri, Nathan Schneider. 2009

148 citations recorded by the source corpus.

Massive dense cores (MDCs) are the high-mass equivalent of the so-called dense cores in nearby star-forming regions. With typical sizes of 0.1 pc, they could form either a few high-mass stars, or a cluster of low-mass stars. We present high-angular resolution continuum observations obtained with the IRAM Plateau de Bure interferometer at 1.3 and 3.5 mm towards the six most massive and youngest (IR-quiet) dense cores in the Cygnus X complex. Located at only 1.7 kpc, the Cygnus X region offers the opportunity of reaching small enough scales (of the order of 1700 AU at 1.3 mm) to separate individual collapsing objects, and thus to observe and constrain the result of the fragmentation process. The cores are sub-fragmented with a total of 23 fragments inside 5 cores. Only the most compact MDC, CygX-N63, may host a single proto-stellar object with an envelope as massive as ˜60 M_ȯ. The fragments in the other cores have sizes and separations similar to low-mass pre-stellar condensations and Class 0 young stellar objects in nearby protoclusters, and are most probably self-gravitating objects (M > Mvir). In addition to CygX-N63, a total of 8 objects are found to be probable precursors of OB stars with their envelope masses ranging from 8.4 to 30 M_ȯ inside a FWHM of 4000 AU. The level of fragmentation is globally higher than in the turbulence regulated, monolithic collapse scenario, but it is also not as high as expected in a pure gravo-turbulent scenario where the distribution of mass is dominated by low-mass protostars/stars. Here, the fractions of the total MDC masses in the high-mass proto-stellar fragments are found to be as high as 37, 58, and 100% in CygX-N12, CygX-N53, and CygX-N63, respectively. These high fractions of mass in the proto-stellar fragments are also indicative of a high efficiency of core formation in the MDCs. The increase in the core formation efficiency as a function of average density in the MDCs is proposed to be caused by the increasing importance of self-gravity leading to gravitational collapse on the scale of the MDCs. At the same time, the observed MDCs tend to fragment into a few proto-stellar objects within their central regions. We are therefore probably witnessing the primordial mass segregation of clusters. The physical origin of the fragmentation into a few high-mass objects is not yet clear, and will be investigated in the future by studying the kinematics of the MDCs.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/f12d6926ea1be670b8940a370690c6f75e71736c

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Instrumentation

In Statistical and Nonlinear Physics

Citations in the corpus

Global collapse of molecular clouds as a formation mechanism for the most massive stars (2013, background): “However, given the uncertainties on the dust properties and density profile of cores, MM1 could match the mass of the most massive cores observed, on smaller scales, in Cygnus X (Bontemps et al. 2010).”
COLLAPSE OF MASSIVE MAGNETIZED DENSE CORES USING RADIATION MAGNETOHYDRODYNAMICS: EARLY FRAGMENTATION INHIBITION (2011, background): “In addition, recent observational work (e.g., Hennemann et al. 2009; Bontemps et al. 2010; Longmore et al. 2011) suggests that collapsing massive dense cores are less fragmented than what numerical calculations produce although the limited observational resolution available precludes a definitive…”
RADIATION-HYDRODYNAMIC SIMULATIONS OF THE FORMATION OF ORION-LIKE STAR CLUSTERS. II. THE INITIAL MASS FUNCTION FROM WINDS, TURBULENCE, AND RADIATION (2012, methodology): “…we choose this size scale because it is approximately the spatial resolution of the highest published resolution maps of massive cores (e.g. Beuther & Schilke 2004; Bontemps et al. 2010), though the Atacama Large Millimeter Array (ALMA) will soon produce images at significantly higher resolution.”
Importance of the Initial Conditions for Star Formation - I. Cloud Evolution and Morphology (2010, background): “On small scales ( 1 pc), the observed cores clearly deviate from a uniform density (e.g. Pirogov 2009; Bontemps et al. 2010; Könyves et al. 2010).”
LOW VIRIAL PARAMETERS IN MOLECULAR CLOUDS: IMPLICATIONS FOR HIGH-MASS STAR FORMATION AND MAGNETIC FIELDS (2013, background): “…the respective authors—evolutionary indicators like masers, mid–infrared emission, outflows, infall line profiles, etc., imply active star formation (Plume et al. 1997; Molinari et al. 2000; Beuther et al. 2002; Beltran et al. 2004; Fontani et al. 2005; Bontemps et al. 2010; Csengeri et al. 2011).”
The stellar and sub-stellar IMF of simple and composite populations (2011, background): “Bontemps et al. (2010) show by observation that massive young dense cores in Cygnus X tend to be more fragmented than expected from turbulence regulated monolithic collapse but that they are less fragmented than predicted by gravo-turbulent scenarios and that the fragments do not show a canonical…”
The spine of the swan: a Herschel study of the DR21 ridge and filaments in Cygnus X (2012, background): “It hosts the embedded HII region DR21 (e.g., Roelfsema et al. 1989), the maser source DR21(OH), and massive protostars (Bontemps et al. 2010).”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “However, in other works, focusing on colder infrared-quiet clumps at even earlier evolutionary stages, it is found that the actual masses of the fragments are often significantly larger than the Jeans mass (e.g., Bontemps et al. 2010; Wang et al. 2014; Zhang et al. 2015; Csengeri et al. 2017).”
Ammonia from cold high-mass clumps discovered in the inner Galactic disk by the ATLASGAL survey (2012, background): “This theory of competitive accretion also agrees with observations, which show that the most massive stars of a cluster are located at its centre (Bontemps et al. 2010).”
The ATLASGAL survey: a catalog of dust condensations in the Galactic plane (2013, methodology): “We adopt therefore the so far best observationally derived value of∼ 3± 1× 105 yr by Duarte-Cabral et al. (2013) for the highly embed- ded stage and account for a multiplicity of∼ 2, which has been seen towards MDCs in Cygnus-X at high angular-resolution (Bontemps et al. 2010).”