There have been many studies aiming to reveal the origins of the star–gas misalignment found in galaxies, but there still is a lack of understanding of the contribution from each formation channel candidate. We aim to answer the question by investigating the misaligned galaxies in the Horizon-AGN simulation. There are 27,903 galaxies of stellar mass M* > 1010Me in our sample, of which 5984 are in a group in the halo mass of M200 > 1012Me. We have identified four main formation channels of misalignment and quantified their levels of contribution: mergers (35%), interaction with nearby galaxies (23%), interaction with dense environments or their central galaxies (21%), and secular evolution, including smooth accretion from neighboring filaments (21%). We found in the simulation that the gas, rather than stars, is typically more vulnerable to dynamical disturbances; hence, misalignment formation is mainly due to the change in the rotational axis of the gas rather than stars, regardless of the origin. We have also inspected the lifetime (duration) of the misalignment. The decay timescale of the misalignment shows a strong anticorrelation with the kinematic morphology (V/σ) and the cold gas fraction of the galaxy. The misalignment has a longer lifetime in denser regions, which is linked with the environmental impact on the host galaxy. There is a substantial difference in the length of the misalignment lifetime depending on the origin, and it can be explained by the magnitude of the initial position angle offset and the physical properties of the galaxies.
Bibliographical noteFunding Information:
Much of this work was conducted while S.K.Y. was visiting the University of Sydney, University of Western Australia, University of Melbourne, and Swinburne University through the Astro3D Distinguished Visitor Programme from the Australian government. He thanks the generous support from the program and the hospitality from the host institutes. S.K.Y. acknowledges support from the Korean National Research Foundation (NRF-2020R1A2C3003769). D.J.K. acknowledges support from Yonsei University through Yonsei Honors Scholarship. J.J.B. acknowledges the support of an Australian Research Council Future Fellowship (FT180100231). C.P. thanks S. Prunet for constructive comments. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. This work relied on the HPC resources of the Horizon Cluster hosted by Institut d’Astrophysique de Paris. We warmly thank S. Rouberol for running the cluster on which the simulation was postprocessed.
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All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science