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"Galactic dynamics."
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Kinematics and Dynamics of Galactic Stellar Populations
Stellar dynamics is an interdisciplinary field where mathematics, statistics, physics, and astronomy overlap. The approaches to studying a stellar system include dealing with the collisionless Boltzmann equation, the Chandrasekhar equations, and stellar hydrodynamic equations, which are comparable to the equations of motion of a compressible viscous fluid. Their equivalence gives rise to the closure problem, connected with the higher-order moments of the stellar velocity distribution, which is explained and solved for maximum entropy distributions and for any velocity distribution function, depending on a polynomial function in the velocity variables. On the other hand, the Milky Way kinematics in the solar neighbourhood needs to be described as a mixture distribution accounting for the stellar populations composing the Galactic components. As such, the book offers a statistical study, according to the moments and cumulants of a population mixture, and a dynamical approach, according to a superposition of Chandrasekhar stellar systems, connected with the potential function and the symmetries of the model.
eBook
Rotation curve and mass distribution in the Galaxy from the velocities of objects at distances up to 200 kpc
Three three-component (bulge, disk, halo) model Galactic gravitational potentials differing by the expression for the dark matter halo are considered. The central (bulge) and disk components are described by the Miyamoto–Nagai expressions. The Allen–Santillán (I), Wilkinson–Evans (II), and Navarro–Frenk–White (III) models are used to describe the halo. A set of present-day observational data in the range of Galactocentric distances
R
from 0 to 200 kpc is used to refine the parameters of thesemodels. For the Allen–Santillán model, a dimensionless coefficient
γ
has been included as a sought-for parameter for the first time. In the traditional and modified versions,
γ
= 2.0 and 6.3, respectively. Both versions are considered in this paper. The model rotation curves have been fitted to the observed velocities by taking into account the constraints on the local matter density
ρ
⊙
= 0.1
M
⊙
pc
−3
and the force
K
z
=1.1/2
πG
= 77
M
⊙
pc
−2
acting perpendicularly to the Galactic plane. The Galactic mass within a sphere of radius 50 kpc,
M
G
(
R
≤ 50 kpc) ≈ (0.41 ± 0.12) × 10
12
M
⊙
, is shown to satisfy all three models. The differences between the models become increasingly significant with increasing radius
R
. In model I, the Galactic mass within a sphere of radius 200 kpc at
γ
= 2.0 turns out to be greatest among the models considered,
M
G
(
R
≤ 200 kpc) = (1.45 ±0.30)× 10
12
M
⊙
,
M
G
(
R
≤ 200 kpc) = (1.29± 0.14)× 10
12
M
⊙
at
γ
= 6.3, and the smallest value has been found in model II,
M
G
(
R
≤ 200 kpc) = (0.61 ± 0.12) × 10
12
M
⊙
. In our view, model III is the best one among those considered, because it ensures the smallest residual between the data and the constructed model rotation curve provided that the constraints on the local parameters hold with a high accuracy. Here, the Galactic mass is
M
G
(
R
≤ 200 kpc) = (0.75 ± 0.19) × 10
12
M
⊙
. A comparative analysis with the models by Irrgang et al. (2013), including those using the integration of orbits for the two globular clusters NGC 104 and NGC 1851 as an example, has been performed. The third model is shown to have subjected to a significant improvement.
Journal Article
The Influence of the Galactic Bar on the Dynamics of Globular Clusters
We make use of recent estimates for the parameters of the Milky Way’s halo globular clusters and study the influence of the galactic bar on the dynamics of these clusters by computing their orbits. We use both an axisymmetric and non-axisymmetric galactic potentials, which include the rotating elongated bar/bulge structure. We account for observational errors both in the positions and in the velocities of the globular clusters and explore the influence of the bar on clusters’ evolution. This is contained in the angular momentum–total energy plane, (Lz,E), which is widely exploited as an indicator of the groups of globular clusters that originated from the same accretion event. Particular attention is devoted to the Gaia-Sausage/Enceladus and Pontus structures identified recently as two independent accretion events. Our study shows that it is not possible to identify GSE and Pontus as different merger events.
Journal Article
A Comprehensive Analysis on the Nature of the Spiral Arms in NGC 3686, NGC 4321, and NGC 2403
In theoretical investigations, various mechanisms have been put forward to explain the emergence of spiral patterns in galaxies. One of the few ways to find out the nature of spirals in a particular galaxy is to consider the so-called corotation radius, or corotation resonance. A distinctly defined corotation resonance is likely to indicate the existence of a spiral density wave, while the chaotic distribution of their positions may suggest a dynamic nature to the spiral structure. In this study, we analyzed measurements of the corotation radius obtained using several methods for three galaxies (NGC 3686, NGC 4321, and NGC 2403) that exhibit different morphologies of spiral structures. We also performed independent measurements to estimate the location of the resonance, which allowed us to determine whether each galaxy has a clear corotation radius position. This examination, along with other tests such as stellar age gradient, interlocking resonances, and the radial distribution of metallicity, enables us to understand the mechanism that may be responsible for the formation of spiral arms in the studied galaxies.
Journal Article
The Response of the Inner Dark Matter Halo to Stellar Bars
Barred galaxies constitute about two-thirds of observed disc galaxies. Bars affect not only the mass distribution of gas and stars but also that of the dark matter. An elongation of the inner dark matter halo is known as the halo bar. We aim to characterize the structure of the halo bars, with the goal of correlating them with the properties of the stellar bars. We use a suite of simulated galaxies with various bar strengths, including gas and star formation. We quantify the strengths, shapes, and densities of these simulated stellar bars. We carry out numerical experiments with frozen and analytic potentials in order to understand the role played by a live responsive stellar bar. We find that the halo bar generally follows the trends of the disc bar. The strengths of the halo and stellar bars are tightly correlated. Stronger bars induce a slight increase in dark matter density within the inner halo. Numerical experiments show that a non-responsive frozen stellar bar would be capable of inducing a dark matter bar, but it would be weaker than the live case by a factor of roughly two.
Journal Article
Refinement of the parameters of three selected model Galactic potentials based on the velocities of objects at distances up to 200 kpc
This paper is a continuation of our recent paper devoted to refining the parameters of threecomponent (bulge, disk, halo) axisymmetric model Galactic gravitational potentials differing by the expression for the dark matter halo using the velocities of distant objects. In all models the bulge and disk potentials are described by the Miyamoto–Nagai expressions. In our previous paper we used the Allen–Santillán (I), Wilkinson–Evans (II), and Navarro–Frenk–White (III) models to describe the halo. In this paper we use a spherical logarithmic Binney potential (model IV), a Plummer sphere (model V), and a Hernquist potential (model VI) to describe the halo. A set of present-day observational data in the range of Galactocentric distances
R
from 0 to 200 kpc is used to refine the parameters of the listed models, which are employed most commonly at present. The model rotation curves are fitted to the observed velocities by taking into account the constraints on the local matter density ρ
⊙
= 0.1
M
⊙
pc
−3
and the force
K
z
=1.1
/2
π
G = 77
M
⊙
pc
−2
acting perpendicularly to the Galactic plane. The Galactic mass within spheres of radius 50 and 200 kpc are shown to be, respectively,
M
50
= (0.409 ± 0.020) × 10
12
M
⊙
and
M
200
= (1.395 ± 0.082) × 10
12
M
⊙
in model IV,
M
50
= (0.417 ± 0.034) × 10
12
M
⊙
and
M
200
= (0.469 ± 0.038) × 10
12
M
⊙
in model V, and
M
50
= (0.417 ± 0.032) × 10
12
M
⊙
and
M
200
= (0.641 ± 0.049)× 10
12
M
⊙
in model VI. Model VI looks best among the three models considered here from the viewpoint of the achieved accuracy of fitting the model rotation curves to the measurements. This model is close to the Navarro–Frenk–White model III refined and considered best in our previous paper, which is shown using the integration of the orbits of two globular clusters, Lynga 7 and NGC 5053, as an example.
Journal Article
Accurate Decomposition of Galaxies with Spiral Arms: Dust Properties and Distribution
We analyze three nearby spiral galaxies—NGC 1097, NGC 1566, and NGC 3627—using images from the DustPedia database in seven infrared bands (3.6, 8, 24, 70, 100, 160, and 250 μm). For each image, we perform photometric decomposition and construct a multi-component model, including a detailed representation of the spiral arms. Our results show that the light distribution is well described by an exponential disk and a Sérsic bulge when non-axisymmetric components are properly taken into account. We test the predictions of the stationary density wave theory using the derived models in bands, tracing both old stars and recent star formation. Our findings suggest that the spiral arms in all three galaxies are unlikely to originate from stationary density waves. Additionally, we perform spectral energy distribution (SED) modeling using the hierarchical Bayesian code HerBIE, fitting individual components to derive dust properties. We find that spiral arms contain a significant (>10%) fraction of cold dust, with an average temperature of approximately 18–20 K. The estimated fraction of polycyclic aromatic hydrocarbons (PAHs) declines significantly toward the galactic center but remains similar between the arm and interarm regions.
Journal Article
Quantifying the Unwinding Due to Ram Pressure Stripping in Simulated Galaxies
Galaxies moving through the gas of the intracluster medium (ICM) experience ram pressure stripping, which can leave behind a gas tail. When a disk galaxy receives the wind edge-on, however, the characteristic signature is not a typical jellyfish tail, but rather an unwinding of the spiral arms. We aim to quantify such asymmetries both in the gas and in the stellar component of a simulated galaxy. To this end, we simulate a gas-rich star-forming spiral galaxy moving through a self-consistent ICM gas. The amplitude and location of the asymmetries were measured via Fourier decomposition. We found that the asymmetry is much more evident in the gas component, but it is also measurable in the stars. The amplitude tends to increase with time and the asymmetry radius migrates inwards. We found that, when considering the gas, the spiral arms extend much further and are more unwound than the corresponding stellar arms. Characterizing the unwinding via simulations should help inform the observational criteria used to classify ram pressure stripped galaxies, as opposed to asymmetries induced by other mechanisms.
Journal Article
Accuracy of Analytic Potentials for Orbits of Satellites Around a Milky Way-like Galaxy: Comparison with N-Body Simulations
To study the orbits of satellites, a galaxy can be modeled either by means of a static gravitational potential or by live N-body particles. Analytic potentials allow for fast calculations but are idealized and non-responsive. On the other hand, N-body simulations are more realistic but demand higher computational cost. Our goal is to characterize the regimes in which analytic potentials provide a sufficient approximation and those where N-bodies are necessary. We perform two sets of simulations, using both Gala and Gadget, in order to closely compare the orbital evolution of satellites around a Milky Way-like galaxy. Focusing on the periods when the satellite has not yet been severely disrupted by tidal forces, we find that the orbits of satellites up to 108M⊙ can be reliably computed with analytic potentials to within 5% error if they are circular or moderately eccentric. If the satellite is as massive as 109M⊙ then errors of 9% are to be expected. However, if the orbital radius is smaller than 30 kpc then the results may not be relied upon with the same accuracy beyond 1–2 Gyr.
Journal Article