scholarly journals Stellar scattering and the formation of exponential discs in self-gravitating systems

2020 ◽  
Vol 499 (2) ◽  
pp. 2672-2684
Author(s):  
Jian Wu ◽  
Curtis Struck ◽  
Elena D’Onghia ◽  
Bruce G Elmegreen
Keyword(s):  
Velocity Dispersion ◽  
Stellar Orbits ◽  
Poisson Equations ◽  
Abrupt Changes ◽  
Gradient Solution ◽  
Stellar Velocity ◽  
Zero Entropy ◽  
Profile Changes ◽  
The Stability ◽  
Gravitating Systems

ABSTRACT We show, using the N-body code gadget-2, that stellar scattering by massive clumps can produce exponential discs, and the effectiveness of the process depends on the mass of scattering centres, as well as the stability of the galactic disc. Heavy, dense scattering centres in a less stable disc generate an exponential profile quickly, with a time-scale shorter than 1 Gyr. The profile evolution due to scattering can make a near-exponential disc under various initial stellar distributions. This result supports analytic theories that predict the scattering processes always favour the zero entropy gradient solution to the Jeans/Poisson equations, whose profile is a near-exponential. Profile changes are accompanied by disc thickening, and a power-law increase in stellar velocity dispersion in both vertical and radial directions is also observed through the evolution. Close encounters between stars and clumps can produce abrupt changes in stellar orbits and shift stars radially. These events can make trajectories more eccentric, but many leave eccentricities little changed. On average, orbital eccentricities of stars increase moderately with time.

scholarly journals Velocity dispersion and the stability of galactic disks

1985 ◽  
Vol 106 ◽  
pp. 541-542
Author(s):  
John Kormendy
Keyword(s):  
Global Stability ◽  
Velocity Dispersion ◽  
Spiral Structure ◽  
Marginal Stability ◽  
The Sun ◽  
Stellar Kinematics ◽  
Local Modes ◽  
Stellar Velocity ◽  
The Stability ◽  
Estimated Error

This paper estimates the effect of the stellar velocity dispersion on local and global instabilities in galaxy disks. Measurements of rotation velocities and velocity dispersions are illustrated for the disks of NGC 488 (Illingworth and Kormendy, in preparation), NGC 936 and NGC 1553. These are used to derive the Toomre stability parameter Q, i.e. the ratio of the observed dispersion to that needed for marginal stability against local modes. In both NGC 488 and 1553, Q = 2.5 − 4, depending on the assumed mass-to-light ratio. These values larger than 2 imply that the stellar disks are stable, although the gas in NGC 488 may remain unstable. This is consistent with the observation that both galaxies largely lack coherent spiral structure: NGC 1553 is an SO and NGC 488 a flocculent spiral. The SBO galaxy NGC 936 is more extreme: Q = 5 (estimated error is a factor of two). This is consistent with Sellwood's suggestion that a bar heats the disk until it is too hot to support spiral structure. In contrast to the above galaxies, Toomre has shown that our Galaxy has Q = 1.6 ± 0.5 near the Sun. It is therefore responsive enough to make spiral structure, as observed.We also explore the stellar kinematics of the disk of NGC 1553 as a function of radius. The exceptionally strong lens component in this galaxy is very hot. At half of the radius of the lens the velocity dispersion appears to be large enough to have an effect even on global stability.

scholarly journals STELLAR VELOCITY DISPERSION AND ANISOTROPY OF THE MILKY WAY INNER HALO

2015 ◽  
Vol 813 (2) ◽  
pp. 89 ◽  
Author(s):  
Charles King III ◽  
Warren R. Brown ◽  
Margaret J. Geller ◽  
Scott J. Kenyon
Keyword(s):  
Milky Way ◽  
Velocity Dispersion ◽  
Stellar Velocity

scholarly journals On resolution of the method of directional magnetotelluric soundings

2015 ◽  
Vol 1 (4) ◽  
pp. 82-85
Author(s):  
Михаил Савин ◽  
Mihail Savin
Keyword(s):  
Field Measurement ◽  
Measurement Errors ◽  
Prediction Modeling ◽  
Mathematical Experiment ◽  
Magnetotelluric Soundings ◽  
Geoelectric Model ◽  
Stability Of Solution ◽  
Abrupt Changes ◽  
The Stability ◽  
Electric Mode

The problem is to examine the resolution of directional magnetotelluric soundings (DMTS). Abrupt changes of impedances of electrical and magnetic types in critical region of parameters R~0, J~ωµσ are shown to result in significantly higher resolution of the method as compared with the traditional interpretation using Tikhonov–Cagniard impedance. The stability of solution of DMTS method inverse problem is considered subject to field measurement errors limited the resolution. The minimum of the limits is determined for the conductivity ∆σ/σ small variations. For studying DMTS resolution as applied to MT monitoring of earthquake site the mathematical experiment for three-layer geoelectric model was carried out. When changing the earthquake site conductivity of ∆σ~±10 % variations of reflection coefficient of electric mode are in the range of 20 % that is significantly more than the field measurement error. The possibility for prediction modeling in the context of obtained results is discussed.

Erratum: “Stellar Velocity Dispersion of a Massive Quenching Galaxy at z = 4.01” (2019, ApJL, 885, L34)

2020 ◽  
Vol 894 (1) ◽  
pp. L13
Author(s):  
Masayuki Tanaka ◽  
Francesco Valentino ◽  
Sune Toft ◽  
Masato Onodera ◽  
Rhythm Shimakawa ◽  
...  
Keyword(s):  
Velocity Dispersion ◽  
Stellar Velocity

A LOCAL BASELINE OF THE BLACK HOLE MASS SCALING RELATIONS FOR ACTIVE GALAXIES. II. MEASURING STELLAR VELOCITY DISPERSION IN ACTIVE GALAXIES

2012 ◽  
Vol 201 (2) ◽  
pp. 29 ◽  
Author(s):  
Chelsea E. Harris ◽  
Vardha N. Bennert ◽  
Matthew W. Auger ◽  
Tommaso Treu ◽  
Jong-Hak Woo ◽  
...  
Keyword(s):  
Black Hole ◽  
Velocity Dispersion ◽  
Active Galaxies ◽  
Scaling Relations ◽  
Black Hole Mass ◽  
Mass Scaling ◽  
Stellar Velocity

scholarly journals LLAMA: The MBH–σ⋆ relation of the most luminous local AGNs

2020 ◽  
Vol 634 ◽  
pp. A114 ◽  
Author(s):  
Turgay Caglar ◽  
Leonard Burtscher ◽  
Bernhard Brandl ◽  
Jarle Brinchmann ◽  
Richard I. Davies ◽  
...  
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Velocity Dispersion ◽  
Signal To Noise Ratio ◽  
Broad Line ◽  
Host Galaxies ◽  
Spatially Resolved ◽  
Stellar Velocity ◽  
Black Hole Masses

Context. The MBH–σ⋆ relation is considered a result of coevolution between the host galaxies and their supermassive black holes. For elliptical bulge hosting inactive galaxies, this relation is well established, but there is still discussion concerning whether active galaxies follow the same relation. Aims. In this paper, we estimate black hole masses for a sample of 19 local luminous active galactic nuclei (AGNs; LLAMA) to test their location on the MBH–σ⋆ relation. In addition, we test how robustly we can determine the stellar velocity dispersion in the presence of an AGN continuum and AGN emission lines, and as a function of signal-to-noise ratio. Methods. Supermassive black hole masses (MBH) were derived from the broad-line-based relations for Hα, Hβ, and Paβ emission line profiles for Type 1 AGNs. We compared the bulge stellar velocity dispersion (σ⋆) as determined from the Ca II triplet (CaT) with the dispersion measured from the near-infrared CO (2-0) absorption features for each AGN and find them to be consistent with each other. We applied an extinction correction to the observed broad-line fluxes and we corrected the stellar velocity dispersion by an average rotation contribution as determined from spatially resolved stellar kinematic maps. Results. The Hα-based black hole masses of our sample of AGNs were estimated in the range 6.34 ≤ log MBH ≤ 7.75 M⊙ and the σ⋆CaT estimates range between 73 ≤ σ⋆CaT ≤ 227 km s−1. From the so-constructed MBH − σ⋆ relation for our Type 1 AGNs, we estimate the black hole masses for the Type 2 AGNs and the inactive galaxies in our sample. Conclusions. We find that our sample of local luminous AGNs is consistent with the MBH–σ⋆ relation of lower luminosity AGNs and inactive galaxies, after correcting for dust extinction and the rotational contribution to the stellar velocity dispersion.

scholarly journals The Search for Dark Matter in Draco and Ursa Minor: A Three Year Progress Report

1987 ◽  
Vol 117 ◽  
pp. 153-160 ◽  
Author(s):  
M. Aaronson ◽  
E. Olszewski
Keyword(s):  
Dark Matter ◽  
Velocity Dispersion ◽  
Progress Report ◽  
Radial Velocities ◽  
Circumstantial Evidence ◽  
Dwarf Spheroidal Galaxies ◽  
Ursa Minor ◽  
Stellar Velocity ◽  
Atmospheric Motions ◽  
Matter Component

We report the cumulative results of an on-going effort to measure the stellar velocity dispersion in two nearby dwarf spheroidal galaxies. Radial velocities having an accuracy ≲ 2 km s−1 have now been secured for ten stars in Ursa Minor and eleven stars in Draco (including 16 K giants and 5 C types). Most objects have been observed at two or more epochs. Stars having non-variable velocities yield in both dwarfs a large (∼ 10 km s−1) dispersion. These results cannot be explained by atmospheric motions, and circumstantial evidence suggests that the effects of undetected binaries are also not likely to be important. Instead, it seems that both spheroidals contain a substantial dark matter component, which therefore must be “cold” in form.

scholarly journals Instability Through Anisotropy in Spherical Stellar Systems

1987 ◽  
Vol 127 ◽  
pp. 515-516
Author(s):  
P.L. Palmer ◽  
J. Papaloizou
Keyword(s):  
Growth Rate ◽  
Eigenvalue Problem ◽  
Growth Rates ◽  
Stellar Systems ◽  
Matrix Eigenvalue Problem ◽  
Simple Method ◽  
Anisotropic Models ◽  
Poisson Equations ◽  
Degree Of Anisotropy ◽  
The Stability

We consider the linear stability of spherical stellar systems by solving the Vlasov and Poisson equations which yield a matrix eigenvalue problem to determine the growth rate. We consider this for purely growing modes in the limit of vanishing growth rate. We show that a large class of anisotropic models are unstable and derive growth rates for the particular example of generalized polytropic models. We present a simple method for testing the stability of general anisotropic models. Our anlysis shows that instability occurs even when the degree of anisotropy is very slight.

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