The Collisions of High‐Velocity Clouds with a Magnetized Gaseous Galactic Disk

Santillán, Alfredo; Franco, J.; Martos, M.; Kim, Jong-Soo

doi:10.1086/307065

Cited by 83 publications

(70 citation statements)

References 35 publications

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“…This kind of behaviour is for instance expected from a ram-pressure interaction: the diffuse warm gas has a much larger crosssection for the ram-pressure interaction than the small, dense clumps of the cold medium. Santillan et al (1999) for instance performed MHD simulations to explain head-tail HVCs at z-height of a few kpc. They were successful in explaining head-tail structures.…”

Section: Summary and Discussionmentioning

confidence: 99%

Deep H I observations of the compact high-velocity cloud HVC 125+41-207

Brüns

Kerp

Pagels

2001

A&A

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Abstract.We present deep H i observations of the compact high-velocity cloud HVC 125+41-207 using the 100-m Effelsberg telescope. Our goal was in particular to study the warm neutral medium (WNM) in detail. The Effelsberg data reveals a two phase core/halo structure -one component with a velocity width of Braun & Burton 2000) and one with F W HM ≈ 18 km s −1 . The column density distribution of the warmer component is highly asymmetric and shows a head-tail structure. We performed a Gaussian decomposition of the cloud and found that 52% of the H i mass of the cloud is in the WNM. 24% of the WNM is located in the tail. The overall structure and the systematic variation of the observational parameters radial velocity, velocity dispersion and column density indicate that this cloud is currently interacting with the ambient medium. The Westerbork H i data of this HVC (Braun & Burton 2000) reveals an interesting dense condensation. Assuming that this condensation is virialized and in pressure equilibrium with the ambient medium, we derive a distance of 130 kpc for HVC 125+41-207. Following these considerations, it is possible to constrain the parameters nIGM < 7.8 10 −6 cm −3 and TIGM > 1.1 10 5 K of the intergalactic medium of the Local Group.

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Section: Summary and Discussionmentioning

confidence: 99%

Deep H I observations of the compact high-velocity cloud HVC 125+41-207

Brüns

Kerp

Pagels

2001

A&A

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“…This would explain naturally the systematic velocity shifts observed between the envelopes and nuclei of Complexes A and C (Kalberla & Haud 2006). These complex processes can be investigated by means of hydrodynamical simulations of the HVC-Galactic disk collision (Tenorio-Tagle 1980Comerón & Torra 1992;Santillán et al 1999), for which our models can provide initial conditions. The entry velocities of HVCs into the Galactic layer predicted by our models are much greater than those predicted by a model of Galactic infall (Benjamin & Danly 1997).…”

Section: Analysis Of the ρ -D Relations Calculated Including Drag Forcesmentioning

confidence: 92%

Distribution of the high-velocity clouds in the Galactic halo

Olano¹

2008

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Context. There is a connection between the kinematics and sky distribution of the high velocity clouds (HVCs) and the spatial velocity and orbital plane of the Magellanic Clouds (MCs) that allow us to conclude that most HVCs were ejected from the Clouds, some hundreds of Myrs ago, probably by an encounter between the Large (LMC) and Small Magellanic Cloud (SMC). Aims. Based on the idea that HVCs have progenitors in the MCs, we attempt determine theoretical distances to the HVCs using observed data of the sky positions and radial velocities, and thus to map the spatial distribution of the HVCs. Methods. i) In the context of a kinematical model we have found an analytical formula that gives the distance of an HVC; ii) we have developed two dynamical models in order to study the orbits of the HVCs under the gravitational forces exerted by the Galaxy and the MCs and forces of resistance due to the movement of the HVCs through the Galactic gaseous disk. We have adopted the gravitational potential of the Milky Way given by a dark matter halo (Model 1) plus a massive thick disk partially composed by dark matter (Model 2). By means of a fitting to certain Galactic, MC and HVC conditions we have obtained values for the free parameters of the Models. We have obtained the dynamical distances to the HVCs by constructing the theoretical relationship between the radial velocity and the distance in the line of sight of each HVC. Results. The HVCs can be divided into three major groups: Population MS, Population W and Population A−C. Population MS comprises the Magellanic stream and the leading arm of the Magellanic system. The HVCs of this population are dispersed around the MCs within a volume of ≈200 kpc × 200 kpc × 60 kpc. Population W is situated at a mean distance of ≈15 kpc from the Sun, and has been braked by the gas of the Galactic disk. Population A−C includes Complexes A, C, H, L, M, and ACHVC. The dynamical models give two solutions for the distance of each HVC of Population A−C. The near-distance solutions place Population A−C at ≈6 kpc from the Sun, showing that this chain of HVCs started to interact with the outer parts of the Galactic gaseous disk about 100 Myr ago. While, the spatial distribution of Population A−C represented with the far distances has the shape of a gigantic ring with a radius of ≈125 kpc. Our results support the idea that the LMC-SMC encounter triggered a period of star formation bursts, in which part of the LMC bar was probably formed. The interactions of a few 10 5 massive stars formed in this era with the then-existing low metallicity ISM of the MCs would have created the HVCs

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“…1f of Frick et al (2000). An oblique collision of a high-velocity cloud with a magnetized gaseous disk results in MHD waves, gas vortices, and Parker instabilities, but no prominent hole (Santillán et al 1999). All of this, along with the resulting shock wave collisions, could explain some the peculiarities of the complex, including the discrete epochs of star formation, the dust lane across it, the circular Western rim, and the small perturbations in the HII velocities.…”

Section: The Relative Velocities and Positions Of The Perturbations Amentioning

confidence: 99%

6-m telescope spectroscopic observations of the bubble complex in NGC 6946

Efremov

Pustilnik

Kniazev

et al. 2002

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Abstract. We describe the results of a long-slit spectroscopic study of an unusual star complex in the nearby spiral galaxy NGC 6946 using the SAO 6 m telescope and the Keck 10 m telescope. The complex resembles a circular bubble 600 pc in diameter with a young super star cluster (SSC) near the center. The kinematics of ionized gas is studied through Hα emission with several slit positions. Position-velocity diagrams show two distinct features with high speed motions. One is an irregularly shaped region to the east of the SSC, 270 pc in size, in which most of the Hα emission is blue shifted by 120 km s −1 , and another is a 350 pc shell centered on the SSC with positive and negative velocity shifts of 60 km s −1 . Balmer and He i absorption lines in the SSC give an age of 12-13 Myr, which is consistent with the photometric age but significantly older than the kinematic ages of the high speed regions. The energetics of the SSC and its interaction with the environment are considered. The expansion energies exceed 10 52 ergs, but the power outputs from winds and supernova in the SSC are large enough to account for this. The intensities of Balmer, [N ii], and [S ii] emission lines within and around the complex indicate that shock excitation makes a significant contribution to the emission from the most energetic region.

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The Collisions of High‐Velocity Clouds with a Magnetized Gaseous Galactic Disk

Cited by 83 publications

References 35 publications

Deep H I observations of the compact high-velocity cloud HVC 125+41-207

Deep H I observations of the compact high-velocity cloud HVC 125+41-207

Distribution of the high-velocity clouds in the Galactic halo

6-m telescope spectroscopic observations of the bubble complex in NGC 6946

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