Submillimeter Array Observations of Infrared Dark Clouds: A Tale of Two Cores

Rathborne, J. M.; Jackson, James M.; Zhang, Qizhou; Simon, R.

doi:10.1086/592733

Cited by 63 publications

(99 citation statements)

References 29 publications

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“…In the cores embedded within IRDCs observed by Rathborne et al (2007), three cold condensations are found with masses from 9 to 21 M and sizes ranging from 5200 to 8200 AU (0.026 and 0.041 pc). Rathborne et al (2008) discovered four additional condensations in two other IRDCs with masses ranging from 9 to 29 M but in a larger average size of 12 000 AU (0.06 pc). Zhang et al (2009) investigated G28.34+0.06 where 7 massive condensations were reported with masses ranging from 22 to 97 M inside physical sizes not provided in their article but which are probably significantly larger than the observation beam of 1.2 , which corresponds to 5800 AU.…”

Section: Envelope Masses Of the Proto-stellar Objectsmentioning

confidence: 98%

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

Bontemps¹,

Motte²,

Csengeri³

et al. 2010

A&A

188

337

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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 . 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 > M vir ). 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 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.

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Section: Envelope Masses Of the Proto-stellar Objectsmentioning

confidence: 98%

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

Bontemps¹,

Motte²,

Csengeri³

et al. 2010

A&A

188

337

View full text Add to dashboard Cite

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“…We stress here that the term IR-dark adopted by the authors we refer to is based on MSX observations, and that some sources in the IR-dark subsample may be detected at mid-IR wavelengths with more sensitive telescopes such as Spitzer. We are aware that at least some of our IR-dark sources are mid-IR emitters: G34.43+0.2M1 has a bolometric luminosity of 2 × 10 4 L (Rathborne et al 2008), and so does G24.60+0.1M2 (Rathborne et al 2007). However we keep our classification as it is, noting that this category of molecular clumps will perhaps need further sub-classifications as our knowledge on them improves.…”

Section: The Samplementioning

confidence: 99%

A comparative study of high-mass cluster forming clumps

López-Sepulcre

Cesaroni

Walmsley

2010

A&A

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Aims. We have searched for star formation activity (mainly infall and outflow signatures) in a sample of high-mass molecular clumps (M > 100 M ) in different evolutionary stages and with a wide range of surface densities, with the aim of looking for evolutionary trends and testing observationally recent theoretical models which predict the need for a minimum surface density to form high-mass stars. Methods. Our sample has been selected from single-dish 1.2 mm continuum surveys and is composed of 48 massive molecular clumps, of which 29 are IR-loud and 19 are IR-dark. Each of these has been mapped in the HCO + (1-0), HCN(1-0) and C 18 O(2-1) transitions with the IRAM-30 m telescope on Pico Veleta (Spain). We derive basic parameters (mass, momentum, kinetic energy) for the clumps and their associated outflows and examine the HCO + (1-0) line profiles for evidence of infall or expansion. Results. Molecular outflows have been detected in 75% of our targets from the presence of high-velocity wings in the HCO + (1-0) spectra. These are equally frequent and massive (between ∼1 and ∼100 M ) in IR-dark and IR-loud clumps, implying similar levels of star formation activity in both kinds of objects. A surface density threshold at Σ = 0.3 g cm −2 has been found above which the outflow detection rate increases significantly and the outflows are on average more massive. The infall detection rate in our sample is low, but significantly higher in the IR-dark sub-sample. Our clump mass estimates using the mm dust emission and C 18 O(2-1) are sensitive to the temperature, but assuming a value of 15 K for the IR-dark sub-sample, we find evidence that C 18 O is depleted by a factor ∼4.5. The HCO + (1-0) to HCN(1-0) integrated intensity ratios measured reveal a greater dispersion about the mean value in the IR-dark sub-sample than in the IR-loud by a factor of about 5. We find that a considerable number of IR-dark sources are self-absorbed in HCN(1-0) suggesting that radiative transport effects in the ground state transitions have an important influence on the integrated intensity ratio. Conclusions. Our results indicate that, in terms of outflow frequency and energetics, both IR-dark and IR-loud molecular clumps present equivalent signatures of star formation activity, and that the formation of high-mass stars requires sufficiently high clump surface densities. The higher infall detection rate measured for the IR-dark subsample suggests that these objects could be associated with the onset of star formation.

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“…Such massive core studies require a resolution much higher than this study; they have to resolve the clumps into cores. Several studies on fragmentation were recently carried out using the Plateau du Bure or the SMA interferometers Rathborne et al 2007Rathborne et al , 2008Zhang et al 2009;Swift 2009). They show that the 1.2 mm clumps fragment into smaller cores, but cannot tell at what level the fragmentation halts.…”

Section: Comparison With Theoretical Modelsmentioning

confidence: 99%

“…A&A 515, A42 (2010) Massive stars generally form in clusters (Lada & Lada 2003), of which the precursors are massive clumps or the so-called precluster forming clumps, hereafter just clumps, of a ∼1 pc size. For many massive star-forming regions, we do not yet have the capacity to resolve the clumps into prestellar cores and study the fragmentation ; Rathborne et al 2007Rathborne et al , 2008Zhang et al 2009;Swift 2009). In this paper, we report on the physical parameters of the clumps, such as their morphology, density and temperature.…”

Section: Introductionmentioning

confidence: 99%

Initial phases of massive star formation in high infrared extinction clouds

Rygl

Wyrowski

Schüller

et al. 2010

A&A

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Aims. The earliest phases of massive star formation are found in cold and dense infrared dark clouds (IRDCs). Since the detection method of IRDCs is very sensitive to the local properties of the background emission, we present here an alternative method to search for high column density in the Galactic plane by using infrared extinction maps. Using this method we find clouds between 1 and 5 kpc, of which many were missed by previous surveys. By studying the physical conditions of a subsample of these clouds, we aim at a better understanding of the initial conditions of massive star formation. Methods. We have made extinction maps of the Galactic plane based on the 3.6−4.5 μm color excess between the two shortest wavelength Spitzer IRAC bands, reaching to visual extinctions of ∼100 mag and column densities of 9 × 10 22 cm −2 . From this we compiled a new sample of cold and compact high extinction clouds. We used the MAMBO array at the IRAM 30 m telescope to study the morphology, masses and densities of the clouds and the dense clumps within them. The latter were followed up by pointed ammonia observations with the 100 m Effelsberg telescope, to determine rotational temperatures and kinematic distances. Results. Extinction maps of the Galactic plane trace large scale structures such as the spiral arms. The extinction method probes lower column densities, N H 2 ∼ 4 × 10 22 cm −2 , than the 1.2 mm continuum, which reaches up to N H 2 ∼ 3 × 10 23 cm −2 but is less sensitive to large scale structures. The 1.2 mm emission maps reveal that the high extinction clouds contain extended cold dust emission, from filamentary structures to still diffuse clouds. Most of the clouds are dark in 24 μm, but several show already signs of star formation via maser emission or bright infrared sources, suggesting that the high extinction clouds contain a variety of evolutionary stages. The observations suggest an evolutionary scheme from dark, cold and diffuse clouds, to clouds with a stronger 1.2 mm peak and to finally clouds with many strong 1.2 mm peaks, which are also warmer, more turbulent and already have some star formation signposts.

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Submillimeter Array Observations of Infrared Dark Clouds: A Tale of Two Cores

Cited by 63 publications

References 29 publications

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

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

A comparative study of high-mass cluster forming clumps

Initial phases of massive star formation in high infrared extinction clouds

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