The collisions of high-velocity clouds with the galactic halo

Jelínek, Petr; Hensler, G.

doi:10.1016/j.cpc.2011.01.023

Cited by 6 publications

(5 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Recently, additional ideas have been suggested. Noting the X-rays emission that follows after charge exchange reactions in the heliosphere, Provornikova, Izmodenov, & Lallement (2011) suggest that charge exchange may be important at the interfaces between clouds and hot gas, and, noting the possible role of MHD plasma waves in heating the solar corona Jelínek & Hensler (2011) suggest that plasma waves instigated by collisions between high velocity clouds and halo gas may also be important.…”

Section: Introductionmentioning

confidence: 99%

Modeling the X-Rays Resulting From High-Velocity Clouds

Shelton

Kwak

Henley

2012

ApJ

View full text Add to dashboard Cite

With the goal of understanding why X-rays have been reported near some high velocity clouds, we perform detailed 3 dimensional hydrodynamic and magnetohydrodynamic simulations of clouds interacting with environmental gas like that in the Galaxy's thick disk/halo or the Magellanic Stream. We examine 2 scenarios. In the first, clouds travel fast enough to shock-heat warm environmental gas. In this scenario, the X-ray productivity depends strongly on the speed of the cloud and the radiative cooling rate. In order to shock-heat environmental gas to temperatures of ≥ 10 6 K, cloud speeds of ≥ 300 km/s are required. If cooling is quenched, then the shock-heated ambient gas is X-ray emissive, producing bright X-rays in the 1/4 keV band and some X-rays in the 3/4 keV band due to O VII and other ions. If, in contrast, the radiative cooling rate is similar to that of collisional ionizational equilibrium plasma with solar abundances, then the shocked gas is only mildly bright and for only about 1 Myr. The predicted count rates for the non-radiative case are bright enough to explain the count rate observed with XMM-Newton toward a Magellanic Stream cloud and some enhancement in the ROSAT 1/4 keV count rate toward Complex C, while the predicted count rates for the fully radiative case are not. In the second scenario, the clouds travel through and mix with hot ambient gas. The mixed zone can contain hot gas, but the hot portion of the mixed gas is not as bright as those from the shock-heating scenario.

show abstract

Section: Introductionmentioning

confidence: 99%

Modeling the X-Rays Resulting From High-Velocity Clouds

Shelton

Kwak

Henley

2012

ApJ

View full text Add to dashboard Cite

show abstract

“…On the other hand, simulated IVCs and HVCs that include magnetic fields tend to develop obvious tails, too. See Santillan et al (1999), Kwak et al (2009), Jelínek & Hensler (2011), Kwak et al (2011), andGalyard &Shelton (2016) for examples.…”

Section: Discussionmentioning

confidence: 99%

“…Model HVCs moving through the gradiated density gas within a few kpc of the Galactic midplane develop smooth tails. The tails are short and stocky in most simulations (see Santillan et al 1999;Santillan et al 2004;Jelínek & Hensler 2011), but are longer when the fairly massive clouds are simulated (Galyardt & Shelton 2016). Tails also grow on simulated HVCs traveling through very hot, low density gas, like that expected much farther from the Galactic midplane (see Heitsch & Putman 2009;Kwak et al 2011;Gritton et al 2014;Armillotta et al 2017;Gritton et al 2017;Sander & Hensler 2020), but these tails are generally much more globular and erratic than those on simulated HVCs nearer to the midplane and much blobbier than the Pegasus-Pisces Arch.…”

mentioning

confidence: 99%

The Long Tails of the Pegasus-Pisces Arch Intermediate Velocity Cloud

Shelton,

Williams,

Parker

et al. 2022

Preprint

View full text Add to dashboard Cite

We present hydrodynamic simulations of the Pegasus-Pisces Arch (PP Arch), an intermediate velocity cloud in our Galaxy. The PP Arch, also known as IVC 86-36, is unique among intermediate and high velocity clouds, because its twin tails are unusually long and narrow. Its −50 km s −1 line-of-sight velocity qualifies it as an intermediate velocity cloud, but the tails' orientations indicate that the cloud's total three-dimensional speed is at least ∼ 100 km s −1 . This speed is supersonic in the Reynold's Layer and thick disk. We simulated the cloud as it travels supersonically through the Galactic thick and thin disks at an oblique angle relative to the midplane. Our simulated clouds grow long double tails and reasonably reproduce the H I 21 cm intensity and velocity of the head of the PP Arch. A bow shock protects each simulated cloud from excessive shear and lowers its Reynolds number. These factors may similarly protect the PP Arch and enable the survival of its unusually long tails. The simulations predict the future hydrodynamic behavior of the cloud when it collides with denser gas nearer to the Galactic midplane. It appears that the PP Arch's fate is to deform, dissipate, and merge with the Galactic disk. Unified Astronomy Thesaurus concepts: Interstellar clouds (834); High-velocity clouds (735); Computational astronomy (293); Hydrodynamical simulations (767) 1. INTRODUCTION H I maps of the Pegasus-Pisces region reveal an unusually long, narrow, and straight cloud of intermediate velocity gas extending ∼ 42 o , from (l, b) ∼ (84 o , −34 o ) to (l, b) ∼ (130 o , −62 o ), with an apparent width of ∼ 3 o . It has a distinct head and tapered, bifurcated tail. It appears clearly in the map of H I with velocities between V LSR = −85 and −45 km s −1 in Figure 17 of Wakker (2001) and the maps of H I with velocities between V LSR ∼ −80 and ∼ −30 km s −1 in Figures 2 -4 in Fukui et al. (2021). Their Figure 2 is reproduced here as our Figure 1. Wakker (2001) identified this object as an intermediate velocity cloud (IVC). Wakker (2001) defined IVCs as clouds with local standard of rest velocities of V LSR =∼ 40 km s −1 to 90 km s −1 , but the upper V LSR cut-off has been placed as high as 100 km s −1 by some authors (e.g., Richter 2017). Wakker (2001) named this especially long IVC after its location, calling it the Pegasus-Pisces Arch, abbreviated as the PP Arch. Fukui et al. (2021), who concentrated on the portion that runs from (l, b) ∼ (84 o , −34 o ) to (l, b) ∼ (110 o , −55 o ), named it after the Galactic coordinates of its head, hence IVC 86-36.The Pegasus-Pisces Arch is long, but pennant-shaped, with a broader head and narrower, tapered tails. Its relatively streamline shape contrasts clearly with those of its irregularly shaped low velocity neighbors MBM 53, HLCG 92-35, MBM 54, and MBM 55 (Magnani et al. 1985;Yamamoto et al. 2003;Fukui et al. 2021), which, together, resemble a curved archipelago of small and midsized islands in maps of H I, CO, and tracers of dust.The Pegasus-Pisces Arch is also more streamli...

show abstract

“…Hence, magnetic fields of HVCs are weakly constrained by observations in orientation and strength. Another plausible cause for Faraday rotation can be the compressed magnetic field in the CGM in front of infalling HVCs (Jelínek & Hensler 2011). In this case, the source of Faraday rotation does not belong to the cloud.…”

Section: Magnetic Fieldsmentioning

confidence: 99%

Physical effects on compact high-velocity clouds in the circumgalactic medium

Sander,

Hensler

2020

Preprint

Self Cite

View full text Add to dashboard Cite

We numerically investigate the evolution of compact high-velocity clouds (CHVCs) passing through a hot, tenuous gas representing the highly-ionized circumgalactic medium (CGM) by applying the adaptive-mesh refinement code Flash.The model clouds start from both hydrostatic and thermal equilibrium and are in pressure balance with the CGM. Here, we present 14 models, divided into two mass categories and two metallicities each and different velocities. We allow for selfgravity and thermal conduction or not. All models experience mass diffusion, radiative cooling, and external heating leading to dissociation and ionization.Our main findings are: 1) self-gravity stabilizes clouds against Rayleigh-Taylor instability which are disrupted within 10 sound-crossing times without; 2) clouds can develop Jeans-instable regions internally even though they are initially below Jeans mass; 3) all clouds lose mass by ram pressure and Kelvin-Helmholtz instability; 4) thermal conduction substantially lowers mass-loss rates, by this, extending the clouds' lifetimes, particularly, more than doubling the lifetime of low-mass clouds; 5) thermal conduction leads to continuous, filamentary stripping, while the removed gas is heated up quickly and mixes efficiently with the ambient CGM; 6) without thermal conduction the removed gas consists of dense, cool, clumpy fragments; 7) thermal conduction might prevent CHVCs from forming stars; 8) clouds decelerated by means of drag from the ambient CGM form head-tail shapes and collapse after they reach velocities characteristic for intermediate-velocity clouds.Conclusively, only sophisticated modelling of CHVCs as non-homogeneous and non-isothermal clouds with thermal conduction and self-gravity explains observed morphologies and naturally leads to the suppression of star formation.

show abstract

The collisions of high-velocity clouds with the galactic halo

Cited by 6 publications

References 24 publications

Modeling the X-Rays Resulting From High-Velocity Clouds

Modeling the X-Rays Resulting From High-Velocity Clouds

The Long Tails of the Pegasus-Pisces Arch Intermediate Velocity Cloud

Physical effects on compact high-velocity clouds in the circumgalactic medium

Contact Info

Product

Resources

About