scholarly journals MHD simulations of ram pressure stripping of disk galaxies

2015 ◽  
Vol 11 (S319) ◽  
pp. 143-143
Author(s):  
Mariana Ramos-Martínez ◽  
Gilberto C. Gómez
Keyword(s):  
Wind Tunnel ◽  
Galaxy Evolution ◽  
Large Scale ◽  
Galactic Disk ◽  
Disk Galaxies ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Ram Pressure ◽  
3D Mhd Simulation

AbstractThe removal of ISM of disk galaxies through ram pressure stripping (RPS) has been extensively studied in numerous simulations (see Roediger 2009 and references therein). The models show that RPS has a significant impact on galaxy evolution (truncation of the ISM will lead to a decrease in star formation and a change in galaxy color). Nevertheless, the role of magnetic fields (MFs) on the dynamics of the gas in this process has not been sufficiently studied, although the influence of the MFs on the large scale structure is well established. This motivated us to perform a 3D MHD simulation of a disk galaxy with an isothermal, non-self gravitating and magnetized gaseous disk in equilibrium with a galaxy potential (Allen & Santillán, 1991). We model RPS on the galactic disk under the wind-tunnel approximation with the use of the RAMSES code (Teyssier, 2002) in order to understand the effects of MFs in RPS.

scholarly journals Evolution of auroral substorm as viewed from MHD simulations: dynamics, energy transfer and energy conversion

2020 ◽  
Vol 4 (1) ◽  
Author(s):  
Yusuke Ebihara ◽  
Takashi Tanaka
Keyword(s):  
Energy Transfer ◽  
Large Scale ◽  
A Priori ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
The Earth ◽  
Auroral Substorm ◽  
Transient Disturbances ◽  
Global Mhd Simulation

AbstractAn auroral substorm is a visual manifestation of large-scale, transient disturbances taking place in space surrounding the Earth, and is one of the central issues in the space plasma physics. While a number of studies have been conducted, a unified picture of the overall evolution of the auroral substorm has not been drawn. This paper is aimed to overview the recently obtained results of global magnetohydrodynamics (MHD) simulations in a context of a priori presence of anomalous resistivity leading to magnetic reconnection, and to illuminate what the global MHD simulation can sufficiently reproduce the auroral transients during the auroral substorm. Some auroral transients are found to be seamlessly reproduced by the MHD simulation, including complicated auroral structures moving equatorward during the growth phase, auroral brightening starting to appear near the equatorward border of the preexisting auroral arc, and an auroral surge traveling westward. Possible energy transfer and conversion from the solar wind to the Earth are also overviewed on the basis of the MHD simulation. At least, 4 dynamo regions appear sequentially in the course of the development of the auroral substorm. Although the MHD simulation reproduces some transients, further studies are needed to investigate the role of kinetic processes.

Quasar host galaxies and environments in the GAMA survey

2019 ◽  
Vol 15 (S356) ◽  
pp. 170-170
Author(s):  
Jari Kotilainen
Keyword(s):  
Galaxy Evolution ◽  
Large Scale ◽  
Group Membership ◽  
Host Galaxy ◽  
Host Galaxies ◽  
Cluster Group ◽  
First Results ◽  
Triggering Mechanisms ◽  
Mass Assembly

AbstractWe present first results from our study of the host galaxies and environments of quasars in Galaxy And Mass Assembly (GAMA), a multiwavelength photometric and spectroscopic survey for ∼300,000 galaxies over ∼300 deg2, to a limiting magnitude of r ∼ 20 mag. We use a GAIA-selected sample of ∼350 quasars at z < 0.3 in GAMA. For all the quasars, we determine all surrounding GAMA galaxies and measure their star formation (SF) rate and SF history, and the host galaxy morphology and group membership of the quasars. As a comparison sample of inactive galaxies, we use 1000 subsets of galaxies in GAMA, matched in redshift and galaxy stellar mass to the quasars. We find that quasar activity does not depend on the large-scale environment (cluster/group/void), although quasars tend to prefer satellite location in their environment. Compared to inactive galaxies, quasars are preferentially hosted in bulge-dominated galaxies and have higher SF rates, both overall and averaged over the last 10 and 100 Myr. Quasars also have shorter median SF timescales, shorter median time since the last SF burst, and higher metallicity than inactive galaxies. We discuss these results in terms of triggering mechanisms of the quasar activity and the role of quasars in galaxy evolution.

scholarly journals Relation of polar auroral arcs to magnetotail twisting and IMF rotation: a systematic MHD simulation study

2004 ◽  
Vol 22 (3) ◽  
pp. 951-970 ◽  
Author(s):  
A. Kullen ◽  
P. Janhunen
Keyword(s):  
Magnetic Field ◽  
Simulation Study ◽  
Large Scale ◽  
Detailed Examination ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Sign Change ◽  
Auroral Arcs ◽  
Good Agreement ◽  
Imf Clock Angle

Abstract. We investigate with the help of a magnetohydrodynamic (MHD) model how the large-scale topology of the magnetosphere develops for a constant interplanetary magnetic field (IMF) with different IMF clock angles and for an IMF By sign change during northward IMF. A detailed examination of the topological changes in the tail and the ionosphere for different IMF conditions shows a good agreement with observational results. The MHD simulations for different constant IMF clock angle cases show the expected field-line bending and tail twisting for nonzero IMF By. The tail becomes longer and at its tailward end stronger twisted for IMF Bz>∣By∣ than for IMF Bz

scholarly journals MHD simulations of star-disk magnetospheres and the formation of outflows and jets

2007 ◽  
Vol 3 (S243) ◽  
pp. 265-276
Author(s):  
Christian Fendt
Keyword(s):  
Numerical Simulation ◽  
Stellar Wind ◽  
Large Scale ◽  
Disk Surface ◽  
Time Dependent ◽  
Mhd Simulations ◽  
Tremendous Progress ◽  
Stellar Magnetospheres ◽  
Scale Evolution

AbstractIn this review the recent development concerning the large-scale evolution of stellar magnetospheres in interaction with the accretion disk is discussed. I put emphasis on the generation of outflows and jets from the disk and/or the star. In fact, tremendous progress has occurred over the last decade in the numerical simulation of the star-disk interaction. The role of numerical simulations is essential in this area because the processes involved are complex, strongly interrelated, and often highly time-dependent. Recent MHD simulations suggest that outflows launched from a very concentrated region tend to be un-collimated. I present preliminary results of simulations of large-scale star-disk magnetospheres loaded with matter from the stellar, resp. the disk surface demonstrating how a disk jet collimates the wind from the star and also how the stellar wind lowers the collimation degree of the disk outflow.

scholarly journals Flare particle acceleration in the interaction of twisted coronal flux ropes

2018 ◽  
Vol 611 ◽  
pp. A40 ◽  
Author(s):  
J. Threlfall ◽  
A. W. Hood ◽  
P. K. Browning
Keyword(s):  
Particle Acceleration ◽  
Solar Flares ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Uniform Background ◽  
Energy Gains ◽  
Particle Behaviour

Aim. The aim of this work is to investigate and characterise non-thermal particle behaviour in a three-dimensional (3D) magnetohydrodynamical (MHD) model of unstable multi-threaded flaring coronal loops.Methods. We have used a numerical scheme which solves the relativistic guiding centre approximation to study the motion of electrons and protons. The scheme uses snapshots from high resolution numerical MHD simulations of coronal loops containing two threads, where a single thread becomes unstable and (in one case) destabilises and merges with an additional thread.Results. The particle responses to the reconnection and fragmentation in MHD simulations of two loop threads are examined in detail. We illustrate the role played by uniform background resistivity and distinguish this from the role of anomalous resistivity using orbits in an MHD simulation where only one thread becomes unstable without destabilising further loop threads. We examine the (scalable) orbit energy gains and final positions recovered at different stages of a second MHD simulation wherein a secondary loop thread is destabilised by (and merges with) the first thread. We compare these results with other theoretical particle acceleration models in the context of observed energetic particle populations during solar flares.

scholarly journals Large-scale Gas Dynamical Processes Affecting the Origin and Evolution of Gaseous Galactic Halos

1991 ◽  
Vol 144 ◽  
pp. 417-428
Author(s):  
Paul R. Shapiro
Keyword(s):  
Absorption Line ◽  
Large Scale ◽  
Galactic Halo ◽  
Galactic Disk ◽  
High Redshift ◽  
Cloud Formation ◽  
Galactic Halos ◽  
Origin And Evolution ◽  
Mhd Simulations ◽  
Halo Gas

Observations of galactic halo gas are consistent with an interpretation in terms of the galactic fountain model in which supernova heated gas in the galactic disk escapes into the halo, radiatively cools and forms clouds which fall back to the disk. The results of a new study of several large-scale gas dynamical effects which are expected to occur in such a model for the origin and evolution of galactic halo gas will be summarized, including the following: (1) nonequilibrium absorption line and emission spectrum diagnostics for radiatively cooling halo gas in our own galaxy, as well the implications of such absorption line diagnostics for the origin of quasar absorption lines in galactic halo clouds of high redshift galaxies; (2) numerical MHD simulations and analytical analysis of large-scale explosions and superbubbles in the galactic disk and halo; (3) numerical MHD simulations of halo cloud formation by thermal instability, with and without magnetic field; and (4) the effect of the galactic fountain on the galactic dynamo.

scholarly journals The Strong Transformation of Spiral Galaxies Infalling into Massive Clusters at z~ 0.2

2006 ◽  
Vol 2 (S235) ◽  
pp. 198-198
Author(s):  
L. Cortese ◽  
D. Marcillac ◽  
J. Richard ◽  
H. Bravo-Alfaro ◽  
J.-P. Kneib ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Hubble Space Telescope ◽  
Galactic Disk ◽  
Type System ◽  
Neutral Hydrogen ◽  
Cluster Galaxies ◽  
Tidal Interactions ◽  
Ram Pressure ◽  
Cluster Environment

AbstractWe report the discovery of two peculiar galaxies infalling into the lensing clusters of galaxies Abell 1689 (z~ 0.18) and 2667 (z~ 0.23). Hubble Space Telescope images show extraordinary trails composed by blue bright knots and stellar streams associated with both these systems, an ~L* and ~0.1L* galaxy. Under the combined action of tidal interaction with the cluster potential and of ram pressure by the intra-cluster medium the morphologies and star formation histories of these two galaxies are strongly perturbed. While in the massive system tidal interactions are the dominant effect and are able to produce a sinking of gas towards the galaxy center triggering a strong burst of star formation and changing galaxy's morphology, in the smaller galaxy the effects of gravitation are reduced by ram pressure stripping which blows away the neutral hydrogen from the galactic disk, quenching the star formation activity and transforming a gas rich late type spiral into quiescent disk dominated early type system. This result is a new additional evidence that galaxy mass represents the main driver of galaxy evolution, even during their dive into the harsh cluster environment and can give additional insights on the origin of S0s and dwarf cluster galaxies.

scholarly journals Dynamical Effects of Mergers

1996 ◽  
Vol 171 ◽  
pp. 191-198 ◽  
Author(s):  
J.E. Barnes
Keyword(s):  
Galaxy Evolution ◽  
Elliptical Galaxies ◽  
Disk Galaxies ◽  
Numerical Work ◽  
Orbital Decay ◽  
Interaction Partners ◽  
Theoretical Predictions ◽  
Precise Role ◽  
Insight Into

The bridges and tails of interacting galaxies were elegantly explained when Toomre & Toomre (1972) showed that such features arise from tides acting on disk galaxies. Emboldened by this success, Toomre & Toomre proposed that certain twin-tailed fuzzballs without obvious interaction partners were in fact the merged relics of interacting pairs, and that such relics eventually become elliptical galaxies. Observations of twin-tailed systems found evidence for both their tidal origins and their elliptical destinies (e.g. Schweizer 1986), while self-consistent numerical simulations substantiated theoretical predictions of rapid orbital decay and the elliptical-like outcome of violent relaxation during merging (e.g. Barnes 1988, and references therein). But while our basic picture of merging seems solid, the precise role of this process in galaxy evolution is not so clear. Dynamical studies provide some insight into this issue; at present we can distinguish three levels of reliability in the numerical work: solid results, good bets, and hopeful guesses.

scholarly journals Giant disk galaxies : Where environment trumps mass in galaxy evolution

2015 ◽  
Vol 11 (A29B) ◽  
pp. 738-738
Author(s):  
H. M. Courtois
Keyword(s):  
Galaxy Evolution ◽  
Family Life ◽  
Total Mass ◽  
Final Outcome ◽  
Disk Galaxies ◽  
Nearby Galaxies

There is an ongoing argument regarding galaxies, like there is regarding children, of whether the final outcome is driven primarily by nature or nurture. In the case of galaxies, the total mass plays the role of genetics (nature) and the number of nearby galaxies plays the role of family life (nurture). Untangling the role of each has been particularly difficult for galaxies because the mass of a galaxy is closely tied to its environment.

scholarly journals Wind channeling, magnetospheres, and spindown of magnetic massive stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 320-329
Author(s):  
S. P. Owocki ◽  
A. ud-Doula ◽  
R. H. D. Townsend ◽  
V. Petit ◽  
J. O. Sundqvist ◽  
...  
Keyword(s):  
Large Scale ◽  
Massive Stars ◽  
Line Emission ◽  
Balmer Line ◽  
Closed Loops ◽  
Magnetically Trapped ◽  
Mhd Simulations ◽  
Angular Momentum Loss ◽  
Weak Winds

AbstractA subpopulation (~10%) of hot, luminous, massive stars have been revealed through spectropolarimetry to harbor strong (hundreds to tens of thousand Gauss), steady, large-scale (often significantly dipolar) magnetic fields. This review focuses on the role of such fields in channeling and trapping the radiatively driven wind of massive stars, including both in the strongly perturbed outflow from open field regions, and the wind-fed “magnetospheres” that develop from closed magnetic loops. For B-type stars with weak winds and moderately fast rotation, one finds “centrifugal magnetospheres”, in which rotational support allows magnetically trapped wind to accumulate to a large density, with quite distinctive observational signatures, e.g. in Balmer line emission. In contrast, more luminous O-type stars have generally been spun down by magnetic braking from angular momentum loss in their much stronger winds. The lack of centrifugal support means their closed loops form a “dynamical magnetosphere”, with trapped material falling back to the star on a dynamical timescale; nonetheless, the much stronger wind feeding leads to a circumstellar density that is still high enough to give substantial Balmer emission. Overall, this review describes MHD simulations and semi-analytic dynamical methods for modeling the magnetospheres, the magnetically channeled wind outflows, and the associated spin-down of these magnetic massive stars.

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