Looking for a needle in a haystack: Measuring the length of a stellar bar

Ghosh, Soumavo; Di Matteo, Paola

doi:10.1051/0004-6361/202347763

Cited by 4 publications

(1 citation statement)

References 89 publications

(134 reference statements)

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“…Hereafter we will refer to R 1 as the bar radius or length, as it agrees well with the definition of best estimates for bar lengths in numerical simulations (Ghosh & Di Matteo 2023). Second, once the bar region is determined, it computes the bar pattern speed and the bar phase angle together with their uncertainties using the covariance matrix of the real part of Eq.…”

Section: The Dehnen Methodsmentioning

confidence: 73%

The bar pattern speed of the Large Magellanic Cloud

Jiménez-Arranz,

Chemin,

Romero-Gómez

et al. 2024

A&A

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The internal kinematics of the Large Magellanic Cloud (LMC) have been studied in unprecedented depth thanks to the excellent quality of the mission data, thus revealing the disc's non-axisymmetric structure. We seek to constrain the LMC bar pattern speed using the astrometric and spectroscopic data from the mission. We applied three methods to evaluate the bar pattern speed by measuring it via: the Tremaine-Weinberg (TW) method, the Dehnen method, and a bisymmetric velocity (BV) model. These methods provide additional information on the bar properties, such as the corotation radius as well as the bar length and strength. We tested the validity of the methods with numerical simulations. A wide range of pattern speeds are inferred by the TW method, owing to a strong dependency on the orientation of the galaxy frame and the viewing angle of the bar perturbation. The simulated bar pattern speeds (corotation radii, respectively) are well recovered by the Dehnen method (BV model). Applied to the LMC data, the Dehnen method finds a pattern speed of $ thus corresponding to a bar that barely rotates and is only slightly counter-rotating with respect to the LMC disc. The BV method gives a LMC bar corotation radius of $R_c = 4.20 0.25$ kpc, corresponding to a pattern speed of $ kmskpc. It is not possible to determine which global value best represents an LMC bar pattern speed with the TW method, due to the strong variation with the orientation of the reference frame. The non-rotating bar from the Dehnen method would be at odds with the structure and kinematics of the LMC disc. The BV method result is consistent with previous estimates and gives a bar corotation-to-length ratio of $1.8 0.1$, suggesting that the LMC is hosting a slow bar.

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Section: The Dehnen Methodsmentioning

confidence: 73%

The bar pattern speed of the Large Magellanic Cloud

Jiménez-Arranz,

Chemin,

Romero-Gómez

et al. 2024

A&A

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Bars and boxy/peanut bulges in thin and thick discs

Ghosh,

Fragkoudi,

Di Matteo

et al. 2024

A&A

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Boxy/peanut (b/p) bulges, the vertically extended inner parts of bars, are ubiquitous in barred galaxies in the local Universe, including our own Milky Way. At the same time, the majority of external galaxies and the Milky Way also possess a thick disc. However, the dynamical effect of thick discs in the b/p formation and evolution is not fully understood. Here, we investigate the effect of thick discs in the formation and evolution of b/ps by using a suite of $N$-body models of (kinematically cold) thin and (kinematically hot) thick discs. Within the suite of models, we systematically vary the mass fraction of the thick disc, and the thin-to-thick disc scale length ratio. The b/ps form in almost all our models via a vertical buckling instability, even in the presence of a massive thick disc. The thin disc b/p is much stronger than the thick disc b/p. With an increasing thick-disc mass fraction, the final b/p structure becomes progressively weaker in strength and larger in extent. Furthermore, the time interval between the bar formation and the onset of buckling instability becomes progressively shorter with an increasing thick-disc mass fraction. The breaking and restoration of the vertical symmetry (during and after the b/p formation) show a spatial variation -- the inner bar region restores vertical symmetry rather quickly (after the buckling), while in the outer bar region the vertical asymmetry persists long after the buckling happens. Our findings also predict that at higher redshifts, when discs are thought to be thicker, b/ps would have a more `boxy' appearance than an `X-shaped' one. This remains to be tested in future observations at higher redshifts.

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KRATOS: A large suite of N-body simulations to interpret the stellar kinematics of LMC-like discs

Jiménez-Arranz,

Roca-Fàbrega,

Romero-Gómez

et al. 2024

A&A

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The Large and Small Magellanic Clouds (LMC and SMC, respectively) are the brightest satellites of the Milky Way (MW), and for the last thousand million years they have been interacting with one another. As observations only provide a static picture of the entire process, numerical simulations are used to interpret the present-day observational properties of these kinds of systems, and most of them have been focused on attempting to recreate the neutral gas distribution and characteristics through hydrodynamical simulations. We present KRATOS, a comprehensive suite of 28 open-access pure N-body simulations of isolated and interacting LMC-like galaxies designed for studying the formation of substructures in their discs after interaction with an SMC-mass galaxy. The primary objective of this paper is to provide theoretical models that help us to interpret the formation of general structures in an LMC-like galaxy under various tidal interaction scenarios. This is the first paper of a series dedicated to the analysis of this complex interaction. Simulations are grouped into 11 sets of up to three configurations, with each set containing (1) a control model of an isolated LMC-like galaxy; (2) a model that contains the interaction with an SMC-mass galaxy, and (3) a model where both an SMC-mass and a MW-mass galaxy may interact with the LMC-like galaxy (the most realistic model). In each simulation, we analysed the orbital history between the three galaxies and examined the morphological and kinematic features of the LMC-like disc galaxy throughout the interaction. This includes investigating the disc scale height and velocity maps. When a bar was found to develop, we characterised its strength, length, off-centredness, and pattern speed. The diverse outcomes found in the KRATOS simulations, including the presence of bars, warped discs, and various spiral arm shapes, demonstrate the opportunities they they offer to explore a range of LMC-like galaxy morphologies. These morphologies directly correspond to distinct disc kinematic maps, making them well-suited for a first-order interpretation of the LMC's kinematic maps. From the simulations, we note that tidal interactions can: boost the disc scale height; both destroy and create bars; and naturally explain the off-centre stellar bars. The bar length and pattern speed of long-lived bars are not appreciably altered by the interaction. The high spatial, temporal, and mass resolution used in the KRATOS simulations has been shown to be appropriate for the purpose of interpreting the internal kinematics of LMC-like discs, as evidenced by the first scientific results presented in this work.

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Looking for a needle in a haystack: Measuring the length of a stellar bar

Cited by 4 publications

References 89 publications

The bar pattern speed of the Large Magellanic Cloud

The bar pattern speed of the Large Magellanic Cloud

Bars and boxy/peanut bulges in thin and thick discs

KRATOS: A large suite of N-body simulations to interpret the stellar kinematics of LMC-like discs

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