Magnetohydrodynamic Evolution of H<scp>ii</scp>Regions in Molecular Clouds: Simulation Methodology, Tests, and Uniform Media

Krumholz, Mark R.; Stone, James M.; Gardiner, Thomas A.

doi:10.1086/522665

Cited by 146 publications

(222 citation statements)

References 39 publications

(54 reference statements)

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“…Krumholz et al (2007) present a simulation of an H ii region expanding into a magnetised gas. This simulation shows that magnetic fields suppress the sweeping up of gas perpendicular to magnetic field lines.…”

Section: Morphology and Evolution Of An H II Regionmentioning

confidence: 99%

A gallery of bubbles

Deharveng

Schüller

Anderson

et al. 2010

A&A

358

584

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Context. This study deals with infrared bubbles, the H ii regions they enclose, and triggered massive-star formation on their borders.Aims. We attempt to determine the nature of the bubbles observed by Spitzer in the Galactic plane, mainly to establish if possible their association with massive stars. We take advantage of the very simple morphology of these objects to search for star formation triggered by H ii regions, and to estimate the importance of this mode of star formation.Methods. We consider a sample of 102 bubbles detected by Spitzer-GLIMPSE, and catalogued by Churchwell et al. (2006; hereafter CH06). We use mid-infrared and radio-continuum public data (respectively the Spitzer-GLIMPSE and -MIPSGAL surveys and the MAGPIS and VGPS surveys) to discuss their nature. We use the ATLASGAL survey at 870 μm to search for dense neutral material collected on their borders. The 870 μm data traces the distribution of cold dust, thus of the dense neutral material where stars may form. Results. We find that 86% of the bubbles contain ionized gas detected by means of its radio-continuum emission at 20-cm. Thus, most of the bubbles observed at 8.0 μm enclose H ii regions ionized by O-B2 stars. This finding differs from the earlier CH06 results (∼25% of the bubbles enclosing H ii regions). Ninety-eight percent of the bubbles exhibit 24 μm emission in their central regions. The ionized regions at the center of the 8.0 μm bubbles seem to be devoid of PAHs but contain hot dust. PAH emission at 8.0 μm is observed in the direction of the photodissociation regions surrounding the ionized gas. Among the 65 regions for which the angular resolution of the observations is high enough to resolve the spatial distribution of cold dust at 870 μm, we find that 40% are surrounded by cold dust, and that another 28% contain interacting condensations. The former are good candidates for the collect and collapse process, as they display an accumulation of dense material at their borders. The latter are good candidates for the compression of pre-existing condensations by the ionized gas. Thirteen bubbles exhibit associated ultracompact H ii regions in the direction of dust condensations adjacent to their ionization fronts. Another five show methanol masers in similar condensations. Conclusions. Our results suggest that more than a quarter of the bubbles may have triggered the formation of massive objects.Therefore, star formation triggered by H ii regions may be an important process, especially for massive-star formation.

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Section: Morphology and Evolution Of An H II Regionmentioning

confidence: 99%

A gallery of bubbles

Deharveng

Schüller

Anderson

et al. 2010

A&A

358

584

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“…This process is necessary to prevent the formation of artificial corrugations in the ionization front, as explained in detail in Krumholz et al (2007).…”

Section: Ray Rotationmentioning

confidence: 99%

Smoothed particle hydrodynamics simulations of expanding H II regions

Bisbas¹,

Wünsch²,

Whitworth³

et al. 2009

A&A

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Context. Ionizing radiation plays a crucial role in star formation at all epochs. In contemporary star formation, ionization abruptly raises the pressure by more than three orders of magnitude; the temperature increases from ∼10 K to ∼10 4 K, and the mean molecular weight decreases by a factor of more than 3. This may result in positive feedback, either by compressing pre-existing clouds and rendering them unstable, or by sweeping up gravitationally unstable shells. It may also result in negative feedback (by dispersing residual dense gas). Ionizing radiation from OB stars is also routinely invoked as a means of injecting kinetic energy into the interstellar medium and as a driver of sequential self-propagating star formation in galaxies. Aims. We describe a new algorithm for including the dynamical effects of ionizing radiation in SPH simulations, and we present several examples of how the algorithm can be applied to problems in star formation. Methods. We use the HEALPix software to tessellate the sky and to solve the equation of ionization equilibrium along a ray towards each of the resulting tesserae. We exploit the hierarchical nature of HEALPix to make the algorithm adaptive, so that fine angular resolution is invoked only where it is needed, and the computational cost is kept low. Results. We present simulations of (i) the spherically symmetric expansion of an Hii region inside a uniform-density, non-selfgravitating cloud; (ii) the spherically symmetric expansion of an Hii region inside a uniform-density, self-gravitating cloud; (iii) the expansion of an off-centre Hii region inside a uniform-density, non-self-gravitating cloud, resulting in rocket acceleration and dispersal of the cloud; and (iv) radiatively driven compression and ablation of a core overrun by an Hii region. Conclusions. The new algorithm provides the means to explore and evaluate the role of ionizing radiation in regulating the efficiency and statistics of star formation.

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“…As reported by Krumholz et al (2007), the photoionized gas expands, initially pushing the magnetic field aside because the thermal pressure dominates. However, once the thermal pressure in the ionized gas drops to the level of the magnetic pressure in the neutral gas, the magnetic field returns almost to its initial value and direction.…”

Section: Radiation Mhd Code and Test Casementioning

confidence: 64%

“…We have used this code to study the evolution of an HII region in a uniform magnetic field. This problem was first studied by Krumholz et al (2007) and we adopt their parameters in order to aid comparison, that is, an ionizing source of 10 46.5 photons s −1 , ambient density n 0 = 100 cm −2 and temperature T = 11 K, and uniform magnetic field of strength Top row: Magnetic field strength and direction (black indicates perpendicular to plane). Bottom row: Ionization fraction, temperature and density.…”

Section: Radiation Mhd Code and Test Casementioning

confidence: 99%

Radiation-MHD Simulations of HII Region Expansion in Turbulent Molecular Clouds

Arthur¹,

Henney²,

Mellema

et al. 2010

Proc. IAU

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Abstract. We use numerical simulations to investigate how the expansion of an HII region is affected by an ambient magnetic field. First we consider the test problem of expansion in a uniform medium with a unidirectional magnetic field. We then describe the expansion of an HII region in a turbulent medium, taking as our initial conditions the results of and MHD turbulence simulation. We find that although in the uniform medium case the magnetic field does produce interesting effects over long length and timescales, in the turbulent medium case the main effect of the magnetic field is to reduce the efficiency of fragmentation of the molecular gas.

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Magnetohydrodynamic Evolution of HiiRegions in Molecular Clouds: Simulation Methodology, Tests, and Uniform Media

Cited by 146 publications

References 39 publications

A gallery of bubbles

A gallery of bubbles

Smoothed particle hydrodynamics simulations of expanding H II regions

Radiation-MHD Simulations of HII Region Expansion in Turbulent Molecular Clouds

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