Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection
Galaxy merger timescales are crucial for understanding and modeling galaxy formation in our hierarchically structured Universe. However, previous studies have reported widely varying dependencies of merger timescales on initial orbital parameters and mass ratios at the first crossing of r _vir . Usi...
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2025-01-01
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| author | Kun Xu Y. P. Jing |
| author_facet | Kun Xu Y. P. Jing |
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| description | Galaxy merger timescales are crucial for understanding and modeling galaxy formation in our hierarchically structured Universe. However, previous studies have reported widely varying dependencies of merger timescales on initial orbital parameters and mass ratios at the first crossing of r _vir . Using IllustrisTNG simulations, we find that these dependencies vary with host halo mass, suggesting that discrepancies in prior studies may arise from differences in the systems analyzed. Specifically, in low-mass halos, merger timescales show a stronger dependence on initial orbital parameters, while, in high-mass halos, this dependence weakens. To account for these variations, we present a fitting formula that incorporates host mass dependence, achieving a logarithmic scatter smaller than 0.15 dex. Comparing dark-matter-only and baryonic simulations, we observe similar merger timescales for circular orbits but notable differences for radial orbits. In halos with M _host < 10 ^12.5 h ^−1 M _⊙ , mergers in dark-matter-only runs take longer than in baryonic runs, whereas the trend reverses in more massive halos. We attribute these differences to the competing effects of tidal disruption by central galaxy disks and the resistance of baryonic satellites to tidal stripping. Finally, we extend our model to predict merger timescales from any starting radius within the halo. By fitting the extended model to the entire infall sample, we find that using only the merger sample can underestimate merger timescales, particularly for low mass ratios. Our model provides a valuable tool for improving semianalytical and empirical models of galaxy formation. |
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| spelling | doaj-art-7e37e1b1fc3d4b2e951d2e165c6623582025-08-20T02:35:48ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01986220110.3847/1538-4357/add5f6Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample SelectionKun Xu0https://orcid.org/0000-0002-7697-3306Y. P. Jing1https://orcid.org/0000-0002-4534-3125Center for Particle Cosmology, Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, PA 19104, USA ; kunxu@sas.upenn.eduState Key Laboratory of Dark Matter Physics, Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University , Shanghai 201210, People’s Republic of China ; ypjing@sjtu.edu.cnGalaxy merger timescales are crucial for understanding and modeling galaxy formation in our hierarchically structured Universe. However, previous studies have reported widely varying dependencies of merger timescales on initial orbital parameters and mass ratios at the first crossing of r _vir . Using IllustrisTNG simulations, we find that these dependencies vary with host halo mass, suggesting that discrepancies in prior studies may arise from differences in the systems analyzed. Specifically, in low-mass halos, merger timescales show a stronger dependence on initial orbital parameters, while, in high-mass halos, this dependence weakens. To account for these variations, we present a fitting formula that incorporates host mass dependence, achieving a logarithmic scatter smaller than 0.15 dex. Comparing dark-matter-only and baryonic simulations, we observe similar merger timescales for circular orbits but notable differences for radial orbits. In halos with M _host < 10 ^12.5 h ^−1 M _⊙ , mergers in dark-matter-only runs take longer than in baryonic runs, whereas the trend reverses in more massive halos. We attribute these differences to the competing effects of tidal disruption by central galaxy disks and the resistance of baryonic satellites to tidal stripping. Finally, we extend our model to predict merger timescales from any starting radius within the halo. By fitting the extended model to the entire infall sample, we find that using only the merger sample can underestimate merger timescales, particularly for low mass ratios. Our model provides a valuable tool for improving semianalytical and empirical models of galaxy formation.https://doi.org/10.3847/1538-4357/add5f6Dynamical frictionGalaxy evolutionGalaxy mergersHydrodynamical simulations |
| spellingShingle | Kun Xu Y. P. Jing Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection The Astrophysical Journal Dynamical friction Galaxy evolution Galaxy mergers Hydrodynamical simulations |
| title | Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection |
| title_full | Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection |
| title_fullStr | Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection |
| title_full_unstemmed | Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection |
| title_short | Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection |
| title_sort | describing the nonuniversal galaxy merger timescales in illustristng effects of host halo mass baryons and sample selection |
| topic | Dynamical friction Galaxy evolution Galaxy mergers Hydrodynamical simulations |
| url | https://doi.org/10.3847/1538-4357/add5f6 |
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