Tidal interaction can stop galactic bars: on the LMC non-rotating bar

Abstract

Context: Using Gaia DR3 data, Jiménez-Arranz et al. (2024a) computed the LMC bar pattern speed using three different methods. One of them suggested that the LMC might be hosting a bar that barely rotates, and is slightly counter-rotating with respect to the LMC disc, with a pattern speed of ${\Omega }_p=-1.0\pm 0.5$ km/s/kpc. Aims: To confirm that tidal interactions can trigger the LMC hosting a non-rotating bar due to its interaction with the SMC, which could cause the LMC bar to slow down significantly until it (momentarily) stops. Methods: We analyse a subset of models (K9 and K21) from the KRATOS suite (Jiménez-Arranz et al. 2024b) where we detected non-rotating bars. We make use of two different methods to track the evolution of the bar pattern speed: the program patternSpeed.py (Dehnen et al. 2023), and temporal finite-differences of the change rate the bar major axis' phase angle. Results: In the second LMC-SMC-like pericenter passage of K9, the bar of the LMC-like galaxy weakens to almost disappear and regenerates with a pattern speed that suffers a slowdown from ${\Omega }_p\sim 20$ km/s/kpc to ${\Omega }_p\sim 0$ km/s/kpc in less than 75 Myr. Then, the bar rotates at less than ${\Omega }_p\sim 3-5$ km/s/kpc for around 100 Myr, until it recovers the initial (before interaction) pattern speed of ${\Omega }_p\sim 10$ km/s/kpc. The results for the K21 simulation are comparable. Conclusions: This work is the first direct evidence that galactic bars can be slowed down or even stopped by tidal interaction, which strengthens the possibility of the LMC hosting a non-rotating bar, and can add an alternative formation scenario for observed slow-rotating bars.

arXiv commentSubmitted as a letter to A&A. Comments are welcomed!

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• A Galactic Transformation -- Understanding the SMC's Structural and Kinematic Disequilibrium
• Asymmetries in the LMC velocity maps
• Tidally-induced radial migration waves in LMC-like galaxies
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• The orbital dynamics of the LMC and SMC about the Milky Way