Simulations Of Barred Galaxies Research Articles

Ellipse-fitting in Mock Images of TNG50 Barred Galaxies

Recent studies have utilized the TNG50 simulation to explore barred galaxy morphology. The ellipse-fitting method is commonly used to assess properties of the isophotes in the central region of the disk. This work adapts the ellipse-fitting method to simulated images from TNG50, dealing with the issue of excessively pronounced ellipticities in central regions, whether in mass distribution maps or simulated radiative transfer images. To solve this problem, we introduce synthetic realism in the form of convolution with point spread functions, correcting the misbehavior in central ellipticities. These improvements simplify the application of ellipse-fitting to barred galaxies in the TNG50 simulation, enabling more accurate analysis of properties such as bar length and ellipticity, which would otherwise be more difficult to measure accurately. Thus, we conclude that when measuring shapes of simulated barred galaxies, one should apply realistic smoothing, otherwise the inner ellipticities will not be comparable to observations.

Measuring bar pattern speeds from single simulation snapshots

ABSTRACT We describe methods to measure simultaneously the orientation angle ψ and pattern speed Ω from single snapshots of simulated barred galaxies. Unlike previous attempts, our approach is unbiased, precise, and consistent in the sense that $\psi=\int\Omega \mathop{}\mathrm{d} t$. It can be extended to obtain the rate and axis of rotation, i.e. the vector $\boldsymbol{\Omega}$. We provide computer code implementing our method.

UNCERTAINTIES IN THE DEPROJECTION OF THE OBSERVED BAR PROPERTIES

In observations, it is important to deproject the two fundamental quantities characterizing a bar, i.e., its length ($a$) and ellipticity ($e$), to face-on values before any careful analyses. However, systematic estimation on the uncertainties of the commonly used deprojection methods is still lacking. Simulated galaxies are well suited in this study. We project two simulated barred galaxies onto a 2D plane with different bar orientations and disk inclination angles ($i$). Bar properties are measured and deprojected with the popular deprojection methods in the literature. Generally speaking, deprojection uncertainties increase with increasing $i$. All the deprojection methods behave badly when $i$ is larger than $60^\circ$, due to vertical thickness of the bar. Thus, future statistical studies of barred galaxies should exclude galaxies more inclined than $60^\circ$. At moderate inclination angles ($i\leq60^\circ$), 2D deprojection methods (analytical and image stretching) and Fourier-based methods (Fourier decomposition and bar-interbar contrast) perform reasonably well with uncertainties $\sim10\%$ in both the bar length and ellipticity. Whereas the uncertainties of the 1D analytical deprojection can be as high as $100\%$ in certain extreme case. We find that different bar measurement methods show systematic differences in the deprojection uncertainties. We further discuss the deprojection uncertainty factors with the emphasis on the most important one, i.e., the 3D structure of the bar itself. We construct two triaxial toy bar models that can qualitatively reproduce the results of the 1D and 2D analytical deprojections; they confirm that the vertical thickness of the bar is the main source of uncertainties.

On the Relevance of the Tremaine‐Weinberg Method Applied to an Hα Velocity Field: Pattern Speed Determination in M100 (NGC 4321)

The relevance of the Tremaine-Weinberg (TW) method is tested to measure the bar, spiral and inner structure pattern speeds using a gaseous velocity field. The TW method is applied to various simulated barred galaxies in order to demonstrate its validity in seven different configurations, including star formation or/and dark matter halo. The reliability of the different physical processes involved and of the various observational parameters are also tested. The simulations show that the TW method could be applied to the gaseous velocity fields to get a good estimate of the bar pattern speed, under the condition that regions of shocks are avoided and measurements are confined to regions where the gaseous bar is well formed. We successfully apply the TW method to the \\ha velocity field of the Virgo Cluster Galaxy M100 (NGC 4321) and derive pattern speeds of 55+/-5 km/s/kpc for the nuclear structure, 30+/-2 km/s/kpc for the bar and 20+/-1 km/s/kpc for the spiral pattern, in full agreement with published determinations using the same method or alternative ones.

Detailed comparison of the structures and kinematics of simulated and observed barred galaxies

We examine the observable properties of simulated barred galaxies including radial mass profiles, edge-on structure and kinematics, bar lengths and pattern speed evolution for detailed comparison to real systems. We have run several simulations in which bars are created through inherent instabilities in self-consistent simulations of a realistic disc+halo galaxy model with a disc-dominated, flat rotation curve. These simulations were run at high (N=20M particles) and low (N=500K) resolution to test numerical convergence. We determine the pattern speeds in simulations directly from the phase angle of the bar versus time and the Tremaine-Weinberg method. Fundamental dynamics do not change between the high and low resolution, suggesting that convergence has been reached in this case. We find the higher resolution is needed to simulate structural and kinematic properties accurately. The edge-on view of the higher-resolution system clearly shows the bending instability and formation of a peanut-shaped bulge. We determined bar lengths by different means to determine the simulated bar is fast, with a corotation to bar length ratio under 1.5. Simulated bars in these models form with pattern speeds slower than those observed and slow down during their evolution. Dynamical friction between the bar and dark halo is responsible for this deceleration, as revealed by the transfer of angular momentum between the disc and the halo. However, even though the pattern speed is reduced at later times, the instantaneous scale length of the disc has grown sufficiently for the bar motion to agree with many observations. By using a different model and simulation technique than other authors, we are able to compare the robustness of these methods.