What drives bar rotation? The effect of internal properties and galaxy interactions on bar pattern speeds

Merrow, A ORCID: 0009-0001-9521-417X, Fragkoudi, F ORCID: 0000-0002-0897-3013, Grand, RJJ ORCID: 0000-0001-9667-1340 and Martig, M ORCID: 0000-0001-5454-1492 (2026) What drives bar rotation? The effect of internal properties and galaxy interactions on bar pattern speeds. Monthly Notices of the Royal Astronomical Society, 547 (4). ISSN 0035-8711

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Abstract

One of the main properties of galactic bars is their rotation (or pattern) speed, which is driven by both internal galactic properties, as well as external interactions. To assess the influence of these internal and external drivers on bar rotation in a cosmological setting, we use the Auriga suite of cosmological hydrodynamical zoom-in simulations. We calculate the bar pattern speed and the bar rotation rate – the ratio of corotation radius to bar length – at the time of bar formation and at (Formula presented), and compare these to bar age, bar strength, baryon dominance, galaxy stellar mass, and the history of external galaxy interactions. We find that galaxies which are more baryon dominated at (Formula presented) – and which lie above the observed stellar mass–halo mass abundance matching relation – host faster bars, while more dark matter dominated galaxies host slower bars. Baryon-dominated galaxies also form their bars earlier and their rotation rates stay constant or even decrease over time; this leads to older bars being faster than their younger counterparts – in contrast to the expectation of bar slow-down from dynamical friction imparted by the dark matter halo. We also find a trend in stellar mass, with ‘faster’ bars being hosted in more massive galaxies, which could be driven by the underlying higher baryon-dominance of more massive galaxies. Furthermore, we find that external interactions, such as mergers and flybys, correlate with lower bar rotation rates, particularly for strong interactions that occur around bar formation time. This correlation is relatively weak, leaving internal baryon-dominance as the main driver of fast bar rotation rates.

Item Type:	Article
Uncontrolled Keywords:	methods: numerical; galaxies: bar; galaxies: disc; galaxies: evolution; galaxies: interactions; galaxies: kinematics and dynamics; astro-ph.GA; astro-ph.GA; 5107 Particle and High Energy Physics; 51 Physical Sciences; 5107 Particle and High Energy Physics; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	19 February 2026
Date of first compliant Open Access:	12 June 2026
Date Deposited:	12 Jun 2026 14:39
Last Modified:	12 Jun 2026 14:39
DOI or ID number:	10.1093/mnras/stag371
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28836

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