Papers › The GECKOS Survey: Identifying kinematic sub-structures in edge-on galaxies

The GECKOS Survey: Identifying kinematic sub-structures in edge-on galaxies

5 Nov 2024arXiv:2411.03430links table onlyarchive 2025-07-28

A. Fraser-McKelvie, J. van de Sande, D. A. Gadotti, E. Emsellem, T. Brown, D. B. Fisher, M. Martig, M. Bureau, O. Gerhard, A. J. Battisti, J. Bland-Hawthorn, A. Boecker, B. Catinella, F. Combes, L. Cortese, S. M. Croom, T. A. Davis, J. Falcón-Barroso, F. Fragkoudi, K. C. Freeman, M. R. Hayden, R. McDermid, B. Mazzilli Ciraulo, J. T. Mendel, F. Pinna, A. Poci, T. H. Rutherford, C. de Sá-Freitas, L. A. Silva-Lima, L. M. Valenzuela, G. van de Ven, Z. Wang, A. B. Watts

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The vertical evolution of galactic discs is governed by the sub-structures within them. We examine the diversity of kinematic sub-structure present in the first 12 galaxies observed from the GECKOS survey, a VLT/MUSE large programme providing a systematic study of 36 edge-on, Milky Way-mass disc galaxies. Employing the nGIST analysis pipeline, we derive the mean line-of-sight stellar velocity (V_⋆), velocity dispersion (σ_⋆), skew (h₃), and kurtosis (h₄) for the sample, and examine 2D maps and 1D line profiles. Visually, the majority of this sample (8/12) are found to possess boxy-peanut bulges and host the corresponding kinematic structure predicted for stellar bars viewed in projection. Four galaxies exhibit strong evidence for the presence of nuclear discs, including central h₃-V_⋆ sign mismatch, `croissant'-shaped central depressions in σ_⋆ maps, strong gradients in h₃, and positive h₄ plateaus over the expected nuclear disc extent. The strength of the h₃ feature corresponds to the size of the nuclear disc, measured from the h₃ turnover radius. We can explain the features within the kinematic maps of all sample galaxies via disc structure(s) alone. We do not find any need to invoke the existence of dispersion-dominated bulges. Obtaining the specialised data products for this paper and the broader GECKOS survey required significant development of existing integral field spectroscopic (IFS) analysis tools. Therefore, we also present the nGIST pipeline: a modern, sophisticated, and easy-to-use pipeline for the analysis of galaxy IFS data. We conclude that the variety of kinematic sub-structures seen in GECKOS galaxies requires a contemporary view of galaxy morphology, expanding on the traditional view of galaxy structure, and uniting the kinematic complexity observed in the Milky Way with the extragalactic.

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