The GECKOS survey: Identifying kinematic sub-structures in edge-on galaxies
Astronomy & Astrophysics EDP Sciences 700 (2025) ARTN A237
Abstract:
The vertical evolution of galactic discs is governed by the sub-structures within them. Several of these features, including bulges and kinematically distinct discs, are best studied in edge-on galaxies, as the viewing angle allows the easier separation of component light. For this work, we examined 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 N GIST analysis pipeline, we derived the mean luminosity-weighted line-of-sight stellar velocity ( V ⋆ ), velocity dispersion ( σ ⋆ ), skew ( h 3 ), and kurtosis ( h 4 ) for the sample, and examined 2D maps and 1D line profiles. Common clear kinematic signatures were observed: all galaxies display h 3 – V ⋆ sign mismatches in the outer disc regions consistent with a (quasi-)axisymmetric, rotating disc of stars. After scrutinising visual morphologies, we found that the majority of this sample (8/12) possess boxy-peanut bulges and host the corresponding kinematic structure predicted for stellar bars viewed in projection. Inferences were made on the bar viewing angle with respect to the line of sight from the strength of these kinematic indicators; we found one galaxy whose bar is close to side-on with respect to the observer, and two that are close to end-on. Four galaxies exhibit strong evidence for the presence of nuclear discs, including central h 3 – V ⋆ profile anti-correlations, croissant-shaped central depressions in σ ⋆ maps, strong gradients in h 3 , and positive h 4 plateaus over the expected nuclear disc extent. The strength of the h 3 feature corresponds to the size of the nuclear disc, measured from the h 3 turnover radius, taking into account geometric effects. We can explain the features within the kinematic maps of the four unbarred galaxies via disc structure(s) alone. We do not find any need to invoke the existence of dispersion-dominated bulges in any of the sample galaxies. 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 N GIST pipeline: a modern, sophisticated, and easy-to-use pipeline for the analysis of galaxy IFS data, and the key tool employed by the GECKOS survey for producing value-added data products. 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.Lopsidedness in early-type galaxies: the role of the m = 1 multipole in isophote fitting and strong lens modelling
Monthly Notices of the Royal Astronomical Society Oxford University Press 540:4 (2025) 3281-3288
Abstract:
The surface brightness distribution of massive early-type galaxies (ETGs) often deviates from a perfectly elliptical shape. To capture these deviations in their isophotes during an ellipse fitting analysis, Fourier modes of order are often used. In such analyses, the centre of each ellipse is treated as a free parameter which may result in offsets from the centre of light, particularly for ellipses in the outer regions. This complexity is not currently accounted for in the mass models used in either strong gravitational lensing or galactic dynamical studies. In this work, we adopt a different approach, using the Fourier mode to account for this complexity while keeping the centres of all perturbed ellipses fixed, showing that it fits the data equally well. We applied our method to the distribution of light emission to a sample of ETGs from the MASSIVE survey and found that the majority have low amplitudes, below 2 per cent. Five out of the 30 galaxies we analysed have high amplitudes, ranging from 2 to 10 per cent in the outer parts ( kpc), all of which have a physically associated companion. Based on our findings, we advocate the use of the multipole in the mass models used in strong lensing and dynamical studies, particularly for galaxies with recent or ongoing interactions.The MAGPI Survey: the subtle role of environment and not-so-subtle impact of generations of stars on galaxy dynamics
ArXiv 2501.08461 (2025)
The MAGPI Survey: The subtle role of environment and not-so-subtle impact of generations of stars on galaxy dynamics
Publications of the Astronomical Society of Australia Cambridge University Press (CUP) 42 (2025) e035
The GECKOS Survey: identifying kinematic sub-structures in edge-on galaxies
(2024)