Structure of evolved cluster-forming regions

Rolffs, R.; Schilke, P.; Wyrowski, F.; Menten, K. M.; Güsten, R.; Bisschop, S. E.

doi:10.1051/0004-6361/201015367

Cited by 38 publications

(75 citation statements)

References 70 publications

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“…The data points can be roughly fitted by a function f (x) = a · x b + c with an exponent of b = −1.3±0.5 and a constant c = (35±11) K for θ > 6 in the outer parts or envelope where the temperature gradient becomes flat. This is consistent with models of hot cores which predict a steep increase inwards (Rolffs et al 2011). The profile could be affected by the fit function, where in the optical thick limit, T and θ are inversely proportional to each other with T ∝ 1/θ, but this only concerns few molecules.…”

Section: General Remarkssupporting

confidence: 88%

Molecular line survey of the high-mass star-forming region NGC 6334I withHerschel/HIFI and the Submillimeter Array

Zernickel

Schilke

Schmiedeke

et al. 2012

A&A

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107

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Aims. We aim at deriving the molecular abundances and temperatures of the hot molecular cores in the high-mass star-forming region NGC 6334I and consequently deriving their physical and astrochemical conditions. Methods. In the framework of the Herschel guaranteed time key program CHESS (Chemical HErschel Surveys of Star forming regions), NGC 6334I is investigated by using the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory. A spectral line survey is carried out in the frequency range 480-1907 GHz, and further auxiliary interferometric data from the Submillimeter Array (SMA) in the 230 GHz band provide spatial information for disentangling the different physical components contributing to the HIFI spectrum. The spectral lines in the processed Herschel data are identified with the aid of former surveys and spectral line catalogs. The observed spectrum is then compared to a simulated synthetic spectrum, assuming local thermal equilibrium, and best fit parameters are derived using a model optimization package. Results. A total of 46 molecules are identified, with 31 isotopologues, resulting in about 4300 emission and absorption lines. Highenergy levels (E u > 1000 K) of the dominant emitter methanol and vibrationally excited HCN (ν 2 = 1) are detected. The number of unidentified lines remains low with 75, or <2% of the lines detected. The modeling suggests that several spectral features need two or more components to be fitted properly. Other components could be assigned to cold foreground clouds or to outflows, most visible in the SiO and H 2 O emission. A chemical variation between the two embedded hot cores is found, with more N-bearing molecules identified in SMA1 and O-bearing molecules in SMA2. Conclusions. Spectral line surveys give powerful insights into the study of the interstellar medium. Different molecules trace different physical conditions like the inner hot core, the envelope, the outflows or the cold foreground clouds. The derived molecular abundances provide further constraints for astrochemical models.

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Section: General Remarkssupporting

confidence: 88%

Molecular line survey of the high-mass star-forming region NGC 6334I withHerschel/HIFI and the Submillimeter Array

Zernickel

Schilke

Schmiedeke

et al. 2012

A&A

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107

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“…Nevertheless, clear global infall at clump scale is difficult to detect (López-Sepulcre et al 2010;Reiter et al 2011) since local star formation also creates infall and outflow signatures. Infall rates of star-forming clumps are observed to be small, about 10% of the free-fall velocity (Rolffs et al 2011;Tan et al 2014;Wyrowski et al 2016), supporting a quasi-static picture. Rygl et al (2013) suggested that the infall and outflow only become evident when the clump-cloud column density contrast exceeds 2 and, at more evolved stage, the infall is halted.…”

Section: Introductionmentioning

confidence: 71%

Formation of a protocluster: A virialized structure from gravoturbulent collapse

Lee

Hennebelle

2016

A&A

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Context. Most stars are born in the gaseous protocluster environment where the gas is reprocessed after the global collapse from the diffuse molecular cloud. The knowledge of this intermediate step gives more accurate constraints on star formation characteristics. Aims. We demonstrate that a virialized globally supported structure, in which star formation happens, is formed out of a collapsing molecular cloud, and we derive a mapping from the parent cloud parameters to the protocluster to predict its properties with a view to confront analytical calculations with observations and simulations. Methods. We decomposed the virial theorem into two dimensions to account for the rotation and the flattened geometry. Equilibrium was found by balancing rotation, turbulence, and self-gravity, while turbulence was maintained through accretion driving and it dissipates in one crossing time. We estimated the angular momentum and the accretion rate of the protocluster from the parent cloud properties.Results. The two-dimensional virial model predicts the size and velocity dispersion given the mass of the protocluster and that of the parent cloud. The gaseous protoclusters lie on a sequence of equilibrium with the trend R ∼ M 0.5 with limited variations, depending on the evolutionary stage, parent cloud, and parameters that are not well known, such as turbulence driving efficiency by accretion and turbulence anisotropy. The model reproduces observations and simulation results successfully. Conclusions. The properties of protoclusters follow universal relations and they can be derived from that of the parent cloud. The gaseous protocluster is an important primary stage of stellar cluster formation, and should be taken into account when studying star formation. Using simple estimates to infer the peak position of the core mass function (CMF) we find a weak dependence on the cluster mass, suggesting that the physical conditions inside protoclusters may contribute to set a CMF, and by extension an initial mass function (IMF), that appears to be independent of the environment.

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“…We use the tabulated dust opacity from Ossenkopf & Henning (1994) for dust without grain mantles and no coagulation, as found to best fit the Sagittarius B2 region by Rolffs et al (2011b). Including the free-free emission we cover the frequency range from 40 GHz up to 4 THz.…”

Section: Images and Post-processingmentioning

confidence: 99%

The physical and chemical structure of Sagittarius B2

Schmiedeke

Schilke

Möller

et al. 2016

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Context. We model the dust and free-free continuum emission in the high-mass star-forming region Sagittarius B2. Aims. We want to reconstruct the 3D density and dust temperature distribution, as a crucial input to follow-up studies of the gas velocity field and molecular abundances. Methods. We employ the 3D radiative transfer program RADMC-3D to calculate the dust temperature self-consistently, providing a given initial density distribution. This density distribution of the entire cloud complex is then recursively reconstructed, based on available continuum maps, including both single-dish and high-resolution interferometric maps that cover a wide frequency range (ν = 40 GHz−4 THz). The model covers spatial scales from 45 pc down to 100 au, i.e., a spatial dynamic range of 10 5 . Results. We find that the density distribution of Sagittarius B2 can be reasonably well fitted by applying a superposition of spherical cores with Plummer-like density profiles. To reproduce the spectral energy distribution, we position Sgr B2(N) along the line of sight behind the plane containing Sgr B2(M). We find that the entire cloud complex comprises a total gas mass of 8.0 × 10 6 M within a diameter of 45 pc. This corresponds to an averaged gas density of 170 M pc −3 . We estimate stellar masses of 2400 M and 20 700 M and luminosities of 1.8 × 10 6 L and 1.2 × 10 7 L for Sgr B2(N) and Sgr B2(M), respectively. We report H 2 column densities of 2.9 × 10 24 cm −2 for Sgr B2(N) and 2.5 × 10 24 cm −2 for Sgr B2(M) in a 40 beam. For Sgr B2(S), we derive a stellar mass of 1100 M , a luminosity of 6.6 × 10 5 L , and an H 2 column density of 2.2 × 10 24 cm −2 in a 40 beam. We calculate a star formation efficiency of 5% for Sgr B2(N) and 50% for Sgr B2(M). This indicates that most of the gas content in Sgr B2(M) has already been converted to stars or dispersed.

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Structure of evolved cluster-forming regions

Cited by 38 publications

References 70 publications

Molecular line survey of the high-mass star-forming region NGC 6334I withHerschel/HIFI and the Submillimeter Array

Molecular line survey of the high-mass star-forming region NGC 6334I withHerschel/HIFI and the Submillimeter Array

Formation of a protocluster: A virialized structure from gravoturbulent collapse

The physical and chemical structure of Sagittarius B2

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