arXiv subjects

Viktor D. Zozulia

Publications and source records attributed to Viktor D. Zozulia.

5 recordsLinked to original sources

arXiv2026

GalPort: Investigation of the bar in action-angle space

GalPort is a Python package for analysing the orbital dynamics of evolving disc galaxy numerical models in action-angle space. The package implements novel numerical methods for efficiently estimating actions, angles, and frequencies across different, particle-specific timescales: on the scale of radial or vertical oscillation and on the resonant libration/circulation timescale. The algorithm allows calculation of these dynamic quantities simultaneously at all time steps of the simulated galactic evolution. With this tool, one can trace orbital behaviour within time-varying galactic potentials and classify orbits (resonantly trapped, circulating, or passing through a resonance) based on their angle evolution. GalPort also includes specialised options for analysing the phase-space structure of a galactic bar in the disc plane and along its major axis. We demonstrate the package's performance on a typical N-body model of a barred galaxy, obtaining the global distributions of actions and frequencies and performing a detailed orbital decomposition. The code is publicly available under the MIT license at: https://github.com/vdzozulia/galport

astro-ph.GA↗

arXiv2025

Phase-space distortion as a key to unraveling galactic bar buckling

For the first time, we investigate the resonant structure of $N$-body galactic bar at the stage of buckling using action-angle variables. We studied the evolution of vertical actions ($J_z$) and angles associated with vertical resonance ($θ_\mathrm{res}=θ_z - θ_R$) for all orbits in the bar. For this purpose, we divide the orbits into types according to the behavior (libration or circulation) of their resonant angle with respect to fixed points $θ_\mathrm{res}=0$ and $π$ (vertical resonance). We show that during buckling, flat bar orbits circulating with increasing $θ_\mathrm{res}$ transformed into banana-shaped librating orbits (resonant capture) or circulating orbits with decreasing $θ_\mathrm{res}$ (resonant heating). The orbital transformation is accompanied by an increase in $J_z$ and the formation of a boxy/peanut-shaped (B/PS) bulge. During buckling, the phase space $J_z - θ_\mathrm{res}$ undergoes a distortion creating an asymmetry in the position of the fixed points $θ_\mathrm{res}=0$ and $π$ and in banana-shaped orbits near these points. The fixed point $θ_\mathrm{res}=0$ may disappear completely. This also breaks the symmetry between the orbits, which are captured into resonance or go into circulation with decreasing $θ_\mathrm{res}$ near $θ_\mathrm{res}=0$ and $π$. At the same time, near $θ_\mathrm{res}=0$, banana-shaped orbits with low vertical action $J_z$ appear. This reopens the path of orbital transformation through the fixed point $θ_\mathrm{res}=0$. The phase space transformation and orbit transformation occur in a coordinated manner and lead to smoothing of phase space perturbations and restoration of symmetry between orbits.

astro-ph.GA↗

arXiv2024

Boxy/peanut shaping of a mature galactic bar in action-angle space

We study vertical resonant trapping and resonant heating of orbits. These two processes both lead to the growth of a boxy/peanut-shaped bulge in a typical $N$-body model. For the first time, we study this by means of the action variables and resonant angles of the actual orbits that compose the model itself. We used the resonant angle instead of the frequency ratio, which allowed us to clearly distinguish between these two processes in numerical simulations. We show that trapping and heating occur simultaneously, at least at the stage of a mature bar, that is, some orbits quickly pass through vertical resonance while at the same time, a substantial number of orbits remains trapped into this stage for a long time. Half of all bar orbits spend more than 2.5 Gyr in vertical resonance over an interval of 4 Gyr. Half of the orbits trapped into the bar over the last 3 Gyr of simulation remain captured in vertical resonance for more than 2 Gyr. We conclude that in the later stages of the bar evolution, the process of vertical trapping dominates in the ongoing process that causes the boxy/peanut shape of a bar in a typical $N$-body model. This contradicts the results of several recent works.

astro-ph.GA↗

arXiv2024

Positive Lynden-Bell derivative as a ticket to the bar trap?

We have translated the results of $N$-body simulations of one barred model into the language of action variables and frequencies. Using this language, we analysed the behaviour of all orbits in the model on a large time scale at the stage of a mature bar. We show that the orbits join the bar while preserving their adiabatic invariant, which takes into account the 3D structure of the orbits. This allows us to apply the concept of the Lynden-Bell derivative for each of these orbits and trace how the sign of the derivative changes, i.e. how asynchronous changes in angular momentum $L_z$ and orbital precession rate $Ω_\mathrm{pr}$ (normal orbital mode) change to synchronous (abnormal mode). The transition to the abnormal mode occurs when $Ω_\mathrm{pr}$ reaches the angular velocity of the pattern $Ω_\mathrm{p}$, after which the orbit becomes stuck in the bar trap. All this happens against the background of secular changes in actions ($L_z$ decreases, $J_\mathrm{R}$ and $J_z$ increase). At the same time, corotation particles near two stable Lagrange points are also subject to secular changes in their actions. They increase $L_z$ and drift to the periphery, shifting corotation outwards. We also show that a change in the orbital mode from normal to abnormal and the trapping of orbits in a bar is possible only when the bar speed decreases with time, regardless of what is causing the bar to slow down. Our findings clarify and expand the picture of bar formation and evolution in numerical models.

astro-ph.GA↗

arXiv2022

B/PS bulges in DESI Legacy edge-on galaxies I: Sample building

We present the biggest up-to-date sample of edge-on galaxies with B/PS bulges and X-structures. The sample was prepared using images from the DESI Legacy catalogue and contains about 2000 galaxies. To find suitable candidates in catalogue, we made the assumption that the residues (original images minus model) of galaxies with B/PS bulges should exhibit a characteristic X-shape. Galaxies with such features were selected by eye and then used as input data for a neural network training, which was applied to a bigger sample of edge-on galaxies. Using the available data and the photometric models from the literature, we investigated the observational and statistical properties of the sample created. Comparing the $B/D$ ratios for galaxies with and without B/PS bulges, we found that the $B/D$ ratio for galaxies from our sample is statistically higher, with typical values in the range $\approx 0.2-0.5$ depending on the decomposition procedure. We studied how the opening angles $φ$ of the X-structure and the length of its rays are distributed in the formed sample and found them to be consistent with previous measurements and predictions from $N$-body models, e.g. $φ\gtrsim 25~°$, but measured here for a much larger number of galaxies. We found a sharp increase in the B/PS bulge fraction for stellar masses $\log M_{\star} \gtrsim 10.4$, but for edge-on galaxies, which complements the results of previous works. The sample can be used in future work to test various bar models and their relationship with B/PS bulges, as well as to study their stability and evolution.

astro-ph.GA↗