The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

By Fr'ed'erique Motte, S. Bontemps, Peter Schilke, Nicola Schneider, K. Menten, D. Broguiere. 2007

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Aims. Our current knowledge of high-mass star formation is mainly based on follow-up studies of bright sources found by IRAS, and is thus biased against its earliest phases, inconspicuous at infrared wavelengths. We therefore started searching, in an unbiased way and in the closest high-mass star-forming complexes, for the high-mass analogs of low-mass pre-stellar cores and class 0 protostars. Methods.We have made an extensive 1.2 mm continuum mosaicing study of the Cygnus X molecular cloud complex using the MAMBO cameras at the IRAM 30 m telescope. The ~3°^(σ2) imaged areas cover all the high-column density (A_V ≥ 15 mag) clouds of this nearby (~1.7 kpc) cloud complex actively forming OB stars. We then compared our millimeter maps with mid-infrared images, and have made SiO(2-1) follow-up observations of the best candidate progenitors of high-mass stars. Results. Our complete study of Cygnus X with ~0.09 pc resolution provides, for the first time, an unbiased census of massive young stellar objects. We discover 129 massive dense cores (FWHM size ~0.1 pc, M_(1.2 mm) = 4-950 M_☉, volume-averaged density ~10^5 cm^(-3), among which ~42 are probable precursors of high-mass stars. A large fraction of the Cygnus X dense cores (2/3 of the sample) remain undetected by the MSX satellite, regardless of the mass range considered. Among the most massive (≥40 M_☉) cores, infrared-quiet objects are driving powerful outflows traced by SiO emission. Our study qualifies 17 cores as good candidates for hosting massive infrared-quiet protostars, while up to 25 cores potentially host high-luminosity infrared protostars. We fail to discover the high-mass analogs of pre-stellar dense cores (~0.1 pc, > 10^4 cm^-3)) in Cygnus X, but find several massive starless clumps (~0.8 pc, 7 × 10^3 cm^(-3)) that might be gravitationally bound. Conclusions. Since our sample is derived from a single molecular complex and covers every embedded phase of high-mass star formation, it gives the first statistical estimates of their lifetime. In contrast to what is found for low-mass class 0 and class I phases, the infrared-quiet protostellar phase of high-mass stars may last as long as their better-known high-luminosity infrared phase. The statistical lifetimes of high-mass protostars and pre-stellar cores (~3 × 10^4 yr and < 10^3 yr) in Cygnus X are one and two order(s) of magnitude smaller, respectively, than what is found in nearby, low-mass star-forming regions. We therefore propose that high-mass pre-stellar and protostellar cores are in a highly dynamic state, as expected in a molecular cloud where turbulent processes dominate.

Subfields: Astronomy and Astrophysics, Instrumentation, Organic Chemistry

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LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION (2010, background): “However, large-scale surveys, e.g. as conducted in the Cygnus-X region (Motte et al. 2007), indicate that high-mass cores are in many aspects similar to scaledup versions of low-mass cores.”
Analytical Theory for the Initial Mass Function: CO Clumps and Prestellar Cores (2008, result): “This is consistent with the densities characteristic of starforming clumps, n̄ 104Y105 cm 3 (André et al. 2007; Motte et al. 2007).”
THE BOLOCAM GALACTIC PLANE SURVEY: SURVEY DESCRIPTION AND DATA REDUCTION (2010, methodology): “MAMBO on the 30 m IRAM telescope has been used at 1.2 mm to map both small, nearby cores (Kauffmann et al. 2008) and more distant regions of more massive star formation (Rathborne et al. 2006; Motte et al. 2007).”
The spine of the swan: a Herschel study of the DR21 ridge and filaments in Cygnus X (2012, background): “This study focusses on the DR21 ridge (also called DR21 filament), the densest and most massive cloud structure in the Cygnus X region (Schneider et al. 2006; Motte et al. 2007; Roy et al. 2011) at a distance of 1.4 kpc (Rygl et al. 2012).”
EVOLUTION OF MASSIVE PROTOSTARS VIA DISK ACCRETION (2010, unknown): “The proposed formation scenarios are being assessed with high-resolution observations of the massive cores and clumps (e.g., Motte et al. 2007; Marseille et al. 2008; Zhang et al. 2009; Bentemps et al. 2010).”
Ammonia from cold high-mass clumps discovered in the inner Galactic disk by the ATLASGAL survey (2012, background): “In contrast, a first attempt to obtain an unbiased sample using a complete dust continuum imaging at the scale of the molecular complex Cygnus X (Motte et al. 2007) was able to derive some more systematic results on the existence of a cold phase (IR-quiet massive dense cores and Class 0-like…”
The simultaneous formation of massive stars and stellar clusters (2009, background): “This is in agreement with the observation of Motte et al. (2007) that rapid supersonic inward motions are required to enhance clump densities to the values seen in massive protostellar cores.”
Clustered and Triggered Star Formation in W5: Observations with Spitzer (2008, background): “In recent surveys of low mass star forming regions (Enoch et al. 2007) and the high mass star forming regions in Cygnus (Motte et al. 2007), typical star-forming dense cores are ∼0.1 pc in size.”
HOW MANY INFRARED DARK CLOUDS CAN FORM MASSIVE STARS AND CLUSTERS? (2010, background): “…dense gas but no radio continuum; Mueller et al. (2002) map water masers embedded in CS clumps of high bolometric luminosity (> 103L⊙); Hill et al. (2005) explore methanol masers and ultra-compact Hii regions; Motte et al. (2007) study the nearby Cygnus-X MSF site (we use their ‘clumps’).”
Fragmentation and mass segregation in the massive dense cores of Cygnus X (2009, methodology): “…confirming the trend suggested by 5 The obtained Mfragtot = 64.3 M is larger than the 58 M obtained from the gaussian fit of the MAMBO data in Motte et al. (2007), but only slightly, and is therefore compatible with all the mass of the MDC in a single object. the efficiencies in Oph A and B2…”
The ATLASGAL survey: a catalog of dust condensations in the Galactic plane (2013, methodology): “This estimate is consistent with other studies (e.g. Motte et al. 2007; Russeil et al. 2010; Motte et al. 2010; Tackenberg et al. 2012) and is one order of magnitude lower than that of low-mass cores (e.g. Enoch et al. 2007; Hatchell & Fuller 2008), suggestingthat massive cores, (precursors of…”
TADPOL: A 1.3 mm SURVEY OF DUST POLARIZATION IN STAR-FORMING CORES AND REGIONS (2013, background): “At a distance of 1.5 kpc (Rygl et al. 2010), Cygnus X is one of the nearest massive star forming complexes in our galaxy (Schneider et al. 2006; Motte et al. 2007).”
EVOLUTION OF MASSIVE PROTOSTARS WITH HIGH ACCRETION RATES (2008, background): “Some recent observations are getting a close look at the initial condition of massive star formation, and have found strong candidates for high-mass pre-stellar cores (e.g., Rathborne, Simon & Jackson 2007; Motte et al. 2007).”
Dynamic star formation in the massive DR21 filament (2010, methodology): “We also recalculated the mass down to the level of 10% of the peak contour Clump-16 taking a mass-averaged temperature of 20 K (rather than the median temperature of Cygnus X clumps, 15 K, used by Motte et al. 2007), which is in closer agreement with NH3 measurements of this clump (Wienen 2008).”
The large APEX bolometer camera LABOCA (2008, background): “These studies can be extended to high-mass star-forming regions (e.g. Motte et al. 2007; Johnstone et al. 2006).”
ATLASGAL - The APEX telescope large area survey of the galaxy at 870 μm (2009, methodology): “This fraction is similar to the results found by Motte et al. (2007) for the Cygnus-X region.”
Initial highlights of the HOBYS key program, the Herschel imaging survey of OB young stellar objects (2010, methodology): “These three objects are among the first massive prestellar cores, since virtually none have been detected in surveys of the Cygnus X and NGC 6334 complexes (Motte et al. 2007; Russeil et al. 2010).”
Cluster-formation in the Rosette molecular cloud at the junctions of filaments (2012, unknown): “Our Rosette observations indicate that clusters preferentially form atfilament junctionsbut cores (and subsequently stars) can also formalong filaments(see also other studies of high-mass SF regions, e.g., the Nessie-nebula (Jackson et al. 2010), W48 (Nguyen Luong et al. 2011) or Cygnus (Motte et al”
Filaments and ridges in Vela C revealed by Herschel: from low-mass to high-mass star-forming sites (2011, background): “Recent work has focused on finding candidate early stage protostars indicative of the earliest stages of high-mass star formation (e.g. Beuther et al. 2002; Hill et al. 2005; Motte et al. 2007; Rathborne et al. 2007).”