Resonant stellar orbits in spiral galaxies. VI - The equilibrium of a stellar disk in the regions of the Lindblad resonances

1978 ◽  
Vol 221 ◽  
pp. 539
Author(s):  
P. O. Vandervoort
Keyword(s):  
Spiral Galaxies ◽  
Stellar Disk ◽  
Stellar Orbits

scholarly journals The Z Velocity Dispersion of Outer H I Disks

1996 ◽  
Vol 169 ◽  
pp. 489-495
Author(s):  
John M. Dickey
Keyword(s):  
Velocity Distribution ◽  
Velocity Dispersion ◽  
Spiral Galaxies ◽  
Thermal State ◽  
Stellar Disk ◽  
Interstellar Gas ◽  
Heating And Cooling ◽  
Outer Disk ◽  
Atomic Gas

The velocity dispersion of the interstellar gas measured perpendicular to the disk in face-on spiral galaxies shows a remarkable consistency. Typically the width of the velocity distribution decreases monotonically with increasing galactic radius through the luminous, stellar disk; but in the outer disk where there is gas but no stars the velocity dispersion is συ ≃ 7 km s−1 with a scatter of 2 km s–1 at most from one position to another and from one galaxy to another. Trying to understand this number raises questions about the thermal state of the H I in outer, gaseous disks. The most important issue is to understand the dominant heating and cooling processes for the atomic gas.

scholarly journals Resonant Stellar Orbits in Spiral Galaxies

1975 ◽  
Vol 69 ◽  
pp. 237-244
Author(s):  
P. O. Vandervoort
Keyword(s):  
Excellent Agreement ◽  
Spiral Galaxy ◽  
Harmonic Balance ◽  
Spiral Galaxies ◽  
Numerical Solutions ◽  
Equations Of Motion ◽  
Analytic Solutions ◽  
Stellar Orbits ◽  
Method Of Harmonic Balance ◽  
Resonance Phenomena

This paper reviews a series of investigations of the orbits of stars in the regions of the Lindblad resonances of a spiral galaxy. The analysis is formulated in an epicyclic approximation. Analytic solutions of the epicyclic equations of motion are obtained by the method of harmonic balance of Bogoliubov and Mitropolsky. These solutions represent the resonance phenomena exhibited by the orbits in generally excellent agreement with numerical solutions.

scholarly journals Anatomy of a buckling galactic bar

2019 ◽  
Vol 629 ◽  
pp. A52 ◽  
Author(s):  
Ewa L. Łokas
Keyword(s):  
Outer Part ◽  
Vertical Direction ◽  
Dark Matter Halo ◽  
Stellar Disk ◽  
Stellar Orbits ◽  
Buckling Instability ◽  
Bending Waves ◽  
Before And After ◽  
The Galaxy ◽  
Circular Frequency

Using N-body simulations we study the buckling instability in a galactic bar forming in a Milky Way-like galaxy. The galaxy is initially composed of an axisymmetric, exponential stellar disk embedded in a spherical dark matter halo. The parameters of the model are chosen so that the galaxy is mildly unstable to bar formation and the evolution is followed for 10 Gyr. A strong bar forms slowly over the first few gigayears and buckles after 4.5 Gyr from the start of the simulation becoming much weaker and developing a pronounced boxy/peanut shape. We measure the properties of the bar at the time of buckling in terms of the mean acceleration, velocity, and distortion in the vertical direction. The maps of these quantities in face-on projections reveal characteristic quadrupole patterns which wind up over a short timescale. We also detect a secondary buckling event lasting much longer and occurring only in the outer part of the bar. We then study the orbital structure of the bar in periods before and after the first buckling. We find that most of the buckling orbits originate from x1 orbits supporting the bar. During buckling the ratio of the vertical to horizontal frequency of the stellar orbits decreases dramatically and after buckling the orbits obey a very tight relation between the vertical and circular frequency: 3ν = 4Ω. We propose that buckling is initiated by the vertical resonance of the x1 orbits creating the initial distortion of the bar that later evolves as kinematic bending waves.

scholarly journals Galactic spiral structure

2009 ◽  
Vol 465 (2111) ◽  
pp. 3425-3446 ◽  
Author(s):  
Charles Francis ◽  
Erik Anderson
Keyword(s):  
Pitch Angle ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Stellar Orbits ◽  
Grand Design ◽  
Galactic Spiral Structure ◽  
Pattern Speed ◽  
Galactic Spiral ◽  
Almost All ◽  
Spiral Arm

We describe the structure and composition of six major stellar streams in a population of 20 574 local stars in the New Hipparcos Reduction with known radial velocities. We find that, once fast moving stars are excluded, almost all stars belong to one of these streams. The results of our investigation have led us to re-examine the hydrogen maps of the Milky Way, from which we identify the possibility of a symmetric two-armed spiral with half the conventionally accepted pitch angle. We describe a model of spiral arm motions that matches the observed velocities and compositions of the six major streams, as well as the observed velocities of the Hyades and Praesepe clusters at the extreme of the Hyades stream. We model stellar orbits as perturbed ellipses aligned at a focus in coordinates rotating at the rate of precession of apocentre. Stars join a spiral arm just before apocentre, follow the arm for more than half an orbit, and leave the arm soon after pericentre. Spiral pattern speed equals the mean rate of precession of apocentre. Spiral arms are shown to be stable configurations of stellar orbits, up to the formation of a bar and/or ring. Pitch angle is directly related to the distribution of orbital eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve to form bars and rings. We show that orbits of gas clouds are stable only in bisymmetric spirals. We conclude that spiral galaxies evolve toward grand design two-armed spirals. We infer from the velocity distributions that the Milky Way evolved into this form about 9 billion years ago (Ga).

scholarly journals Gravitoelectromagnetism and stellar orbits in galaxies

2021 ◽  
pp. 2150102
Author(s):  
Viktor T. Toth
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Gravitational Field ◽  
Magnetic Force ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Observable Effect ◽  
Stellar Orbits ◽  
Gravitational Fields ◽  
The Impact

Beyond the Newtonian approximation, gravitational fields in general relativity can be described using a formalism known as gravitoelectromagnetism. In this formalism, a vector potential, the gravitomagnetic potential, arises as a result of moving masses, in strong analogy with the magnetic force due to moving charges in Maxwell’s theory. Gravitomagnetism can affect orbits in the gravitational field of a massive, rotating body. This raises the possibility that gravitomagnetism may serve as the dominant physics behind the anomalous rotation curves of spiral galaxies, eliminating the need for dark matter. In this essay, we methodically work out the magnitude of the gravitomagnetic equivalent of the Lorentz force and apply the result to the Milky Way. We find that the resulting contribution is too small to produce an observable effect on these orbits. We also investigate the impact of cosmological boundary conditions on the result and find that these, too, are negligible.

scholarly journals Spiral Galaxy - ICM Interactions in the Virgo Cluster

2004 ◽  
Vol 217 ◽  
pp. 370-375 ◽  
Author(s):  
Jeffrey D. P. Kenney ◽  
Hugh Crowl ◽  
Jacqueline van Gorkom ◽  
Bernd Vollmer
Keyword(s):  
Spiral Galaxies ◽  
Virgo Cluster ◽  
Wind Pressure ◽  
Radio Continuum ◽  
Stellar Disk ◽  
Continuum Emission ◽  
The Galaxy ◽  
Show Evidence ◽  
Optical Evidence ◽  
Early Phases

We discuss HI and optical evidence for ongoing ICM-ISM interactions in 6 Hi-deficient Virgo cluster spiral galaxies. One of the clearest cases is the highly inclined Virgo galaxy NGC 4522, which has a normal stellar disk but a truncated gas disk, and lots of extraplanar gas right next to the gas truncation radius in the disk. Unusually strong HI, Hα and radio continuum emission are all detected from the extraplanar gas. The radio continuum polarized flux and spectral index peak on the side opposite the extraplanar gas, suggesting ongoing pressure by the ICM. Four other HI-deficient edge-on Virgo spirals show evidence of extraplanar ISM gas or exhibit asymmetries in their disk HI distributions, but contain much less extraplanar HI than NGC 4522. Comparison with recent simulations suggests this difference may be evolutionary, with large surface densities of extraplanar gas observed only in early phases of an ICM-ISM interaction. In NGC 4569, the Hα image shows 2 effects of ICM pressure on the galaxy ISM. An anomalous arm of HII regions, possibly extraplanar, emerges from the edge of a truncated Hα disk. This resembles the arms seen in simulations which are formed by the combined effects of wind pressure plus rotation. An extended nebulosity near the minor axis, also in the NW, is interpreted as a starburst outflow bubble disturbed by ICM wind pressure.

scholarly journals Quantifying the mixing due to bars

2012 ◽  
Vol 10 (H16) ◽  
pp. 353-353
Author(s):  
Patricia Sanchez-Blazquez
Keyword(s):  
Angular Momentum ◽  
Gas Phase ◽  
Galaxy Evolution ◽  
Spiral Galaxies ◽  
Solar Neighborhood ◽  
Stellar Disk ◽  
Galactic Disks ◽  
Chemical Abundance ◽  
Evolutionary Processes ◽  
Barred Galaxies

AbstractWe will present star formation histories and the stellar and gaseous metallicity gradients in the disk of a sample of 50 face-on spiral galaxies with and without bars observed with the integral field unit spectrograph PMAS. The final aim is to quantify the redistribution of mass and angular momentum in the galactic disks due to bars by comparing both the gas-phase and star-phase metallicity gradients on the disk of barred and non-barred galaxies. Numerical simulations have shown that strong gravitational torque by non-axisymmetric components induce evolutionary processes such as redistribution of mass and angular momentum in the galactic disks (Sellwood & Binney 2002) and consequent change of chemical abundance profiles. If we hope to understand chemical evolution gradients and their evolution we must understand the secular processes and re-arrangement of material by non-axisymmetric components and vice-versa. Furthermore, the re-arrangement of stellar disk material influences the interpretation of various critical observed metrics of Galaxy evolution, including the age-metallicity relation in the solar neighborhood and the local G-dwarf metallicity distribution. Perhaps the most obvious of these aforementioned non-axisymmetric components are bars - at least 2/3 of spiral galaxies host a bar, and possibly all disk galaxies have hosted a bar at some point in their evolution. While observationally it has been found that barred galaxies have shallower gas-phase metallicity gradients than non-barred galaxies, a complementary analysis of the stellar abundance profiles has not yet been undertaken. This is unfortunate because the study of both gas and stars is important in providing a complete picture, as the two components undergo (and suffer from) very different evolutionary processes.

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