Low Virial Parameters in Molecular Clouds: Implications for High-Mass Star Formation and Magnetic Fields

Kauffmann, Jens; Pillai, T.; Goldsmith, Paul F.

doi:10.1088/0004-637x/779/2/185

Cited by 266 publications

(356 citation statements)

References 81 publications

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“…The plot confirms the findings of URQ13, namely that almost all of the sources are supervirial. This is in agreement also with other studies (e.g., Fontani et al 2002;Kauffmann et al 2013) and supports the idea that clumps above ∼10 3 M in high-mass star forming regions are unstable against gravitational collapse.…”

Section: Clump Stabilitysupporting

confidence: 93%

Infrared emission of young HII regions: aHerschel/Hi-GAL study

Cesaroni

Pestalozzi

Beltrán

et al. 2015

A&A

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Context. Investigating the relationship between radio and infrared emission of Hii regions may help shed light on the nature of the ionizing stars and the formation mechanism of early-type stars in general. Aims. We have taken advantage of recent unbiased surveys of the Galactic plane such as Herschel/Hi-GAL and VLA/CORNISH to study a bona fide sample of young Hii regions located in the Galactic longitude range 10 • -65 • by comparing the mid-and far-IR continuum emission to the radio free-free emission at 5 GHz. Methods. We have identified the Hi-GAL counterparts of 230 CORNISH Hii regions and reconstructed the spectral energy distributions of 204 of these by complementing the Hi-GAL fluxes with ancillary data at longer and shorter wavelengths. Using literature data, we obtained a kinematical distance estimate for 200 Hii regions with Hi-GAL counterparts and determined their luminosities by integrating the emission of the corresponding spectral energy distributions. We have also estimated the mass of the associated molecular clumps from the (sub)millimeter flux densities. Results. Our main finding is that for ∼1/3 of the Hii regions the Lyman continuum luminosity appears to be greater than the value expected for a zero-age main-sequence star with the same bolometric luminosity. This result indicates that a considerable fraction of young, embedded early-type stars presents a "Lyman excess" possibly due to UV photons emitted from shocked material infalling onto the star itself and/or a circumstellar disk. Finally, by comparing the bolometric and Lyman continuum luminosities with the mass of the associated clump, we derive a star formation efficiency of 5%. Conclusions. The results obtained suggest that accretion may still be present during the early stages of the evolution of Hii regions, with important effects on the production of ionizing photons and thus on the circumstellar environment. More reliable numerical models describing the accretion process onto massive stars are required to shed light on the origin of the observed Lyman excess.

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Section: Clump Stabilitysupporting

confidence: 93%

Infrared emission of young HII regions: aHerschel/Hi-GAL study

Cesaroni

Pestalozzi

Beltrán

et al. 2015

A&A

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“…Similar trends have been reported in the literature (e.g. Barnes et al 2011;Kauffmann et al 2013;Urquhart et al 2015). We note that all of the HMSF clumps are found in the unstable part of the parameter space, which would suggest that, even if magnetic fields can stabilise the clumps globally (e.g.…”

Section: Virial Parametersupporting

confidence: 89%

SEDIGISM: Structure, excitation, and dynamics of the inner Galactic interstellar medium

Schüller

Csengeri

Urquhart

et al. 2017

A&A

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Context. The origin and life-cycle of molecular clouds are still poorly constrained, despite their importance for understanding the evolution of the interstellar medium. Many large-scale surveys of the Galactic plane have been conducted recently, allowing for rapid progress in this field. Nevertheless, a sub-arcminute resolution global view of the large-scale distribution of molecular gas, from the diffuse medium to dense clouds and clumps, and of their relationship to the spiral structure, is still missing. Aims. We have carried out a systematic, homogeneous, spectroscopic survey of the inner Galactic plane, in order to complement the many continuum Galactic surveys available with crucial distance and gas-kinematic information. Our aim is to combine this data set with recent infrared to sub-millimetre surveys at similar angular resolutions. Methods. The SEDIGISM survey covers 78 deg 2 of the inner Galaxy (−60CO. This isotopologue of CO is less abundant than 12 CO by factors up to 100. Therefore, its emission has low to moderate optical depths, and higher critical density, making it an ideal tracer of the cold, dense interstellar medium. The data have been observed with the SHFI single-pixel instrument at APEX. The observational setup covers the 13 CO(2 -1) and C 18 O(2 -1) lines, plus several transitions from other molecules. Results. The observations have been completed. Data reduction is in progress, and the final data products will be made available in the near future. Here we give a detailed description of the survey and the dedicated data reduction pipeline. To illustrate the scientific potential of this survey, preliminary results based on a science demonstration field covering −20 • ≤ ≤ -18.5 • are presented. Analysis of the 13 CO(2 -1) data in this field reveals compact clumps, diffuse clouds, and filamentary structures at a range of heliocentric distances. By combining our data with data in the (1-0) transition of CO isotopologues from the ThrUMMS survey, we are able to compute a 3D realization of the excitation temperature and optical depth in the interstellar medium. Ultimately, this survey will provide a detailed, global view of the inner Galactic interstellar medium at an unprecedented angular resolution of ∼30 .

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“…Note also that the GMCs are somewhat confined by the pressure of the ambient, uniform density medium. Observed GMCs appear to have smaller virial parameters, ∼1 (e.g., Roman-Duval et al 2010;Kauffmann et al 2013), especially when considering their positionvelocity connected, 13 CO-emitting structures (Hernandez & Tan 2015). Our choice of initializing with a larger kinetic energy content is motivated by the desire to not have rapid global collapse of the clouds within the first few megayears, i.e., the timescale of the collision.…”

Section: Initial Conditionsmentioning

confidence: 99%

GMC Collisions as Triggers of Star Formation. II. 3D Turbulent, Magnetized Simulations

Tan

Nakamura

et al. 2017

ApJ

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We investigate giant molecular cloud collisions and their ability to induce gravitational instability and thus star formation. This mechanism may be a major driver of star formation activity in galactic disks. We carry out a series of 3D, magnetohydrodynamics (MHD), adaptive mesh refinement simulations to study how cloud collisions trigger formation of dense filaments and clumps. Heating and cooling functions are implemented based on photodissociation region models that span the atomic-to-molecular transition and can return detailed diagnostic information. The clouds are initialized with supersonic turbulence and a range of magnetic field strengths and orientations. Collisions at various velocities and impact parameters are investigated. Comparing and contrasting colliding and non-colliding cases, we characterize morphologies of dense gas, magnetic field structure, cloud kinematic signatures, and cloud dynamics. We present key observational diagnostics of cloud collisions, especially: relative orientations between magnetic fields and density structures, like filaments; 13 CO( J=2-1), 13 CO( J=3-2), and 12 CO( J=8-7) integrated intensity maps and spectra; and cloud virial parameters. We compare these results to observed Galactic clouds.

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Low Virial Parameters in Molecular Clouds: Implications for High-Mass Star Formation and Magnetic Fields

Cited by 266 publications

References 81 publications

Infrared emission of young HII regions: aHerschel/Hi-GAL study

Infrared emission of young HII regions: aHerschel/Hi-GAL study

SEDIGISM: Structure, excitation, and dynamics of the inner Galactic interstellar medium

GMC Collisions as Triggers of Star Formation. II. 3D Turbulent, Magnetized Simulations

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