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

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

doi:10.1051/0004-6361/202452891

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

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

Department of Astrophysics

Publications: Contribution to journal › Article › Peer Reviewed

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 nGIST analysis pipeline, we derived the mean luminosity-weighted line-of-sight stellar velocity (V_★), velocity dispersion (σ_★), skew (h₃), and kurtosis (h₄) for the sample, and examined 2D maps and 1D line profiles. Common clear kinematic signatures were observed: all galaxies display h₃ – 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 h₃–V_★ profile anti-correlations, 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, 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 nGIST 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.

Original language	English
Article number	A237
Number of pages	34
Journal	Astronomy and Astrophysics
Volume	700
DOIs	https://doi.org/10.1051/0004-6361/202452891
Publication status	Published - 1 Aug 2025

Funding

Author contribution statement: This project was devised by AFM, with analysis completed by AFM, and some scripts provided by JvdS. Comments were provided by the whole author list. GECKOS data reduction is led by JvdS and AFM, with assistance from EE, LC, BMC, TM, and BC. N GIST development is led by AFM and JvdS, with contributions and testing from TB, AW, ZW, LSL, LC, FP, MM, DG, EE, and CdSF. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 110.24AS. We wish to thank the ESO staff, and in particular the staff at Paranal Observatory, for carrying out the GECKOS observations. The authors wish to thank the anonymous referee, whose careful reading and interpretation of this manuscript resulted in comments that improved its quality. The authors also wish to thank Adrian Bittner for useful conversations, and his blessing to continue the development of the GIST pipeline. We also thank Lodovico Coccato for useful conversations relating to MUSE data reduction and analysis, Alex Vazdekis for his permission to distribute the MILES models with the N GIST package, Livia Casagrande whose Honours work provided useful insights, and Michele Cappellari for useful conversations related to P PXF usage. This research has made use of the NASA/IPAC Extragalactic Database (NED; https://ned.ipac.caltech.edu/ ) operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. This research used the Canadian Advanced Network For Astronomy Research (CANFAR) operated in partnership by the Canadian Astronomy Data Centre and The Digital Research Alliance of Canada with support from the National Research Council of Canada the Canadian Space Agency, CANARIE and the Canadian Foundation for Innovation. Part of this research was conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. AFM gratefully acknowledges the sponsorship provided by the European Southern Observatory through a research fellowship. DAG is supported by STFC grant ST/X001075/1. TAD acknowledges support from the UK Science and Technology Facilities Council through grants ST/S00033X/1 and ST/W000830/1. FP acknowledges support from the Agencia Estatal de Investigación del Ministerio de Ciencia e Innovación (MCIN/AEI/ 10.13039/501100011033) under grant (PID2021-128131NB-I00) and the European Regional Development Fund (ERDF) “A way of making Europe”. FP acknowledges support also from the Horizon Europe research and innovation programme under the Marie Skłodowska-Curie grant “TraNSLate” No 101108180. FF is supported by a UKRI Future Leaders Fellowship (grant no. MR/X033740/1). AP acknowledges support from the Hintze Family Charitable Foundation. LSL acknowledges CAPES for the support through grant 88887.637633/2021-00 and CNPQ through grant 200469/2022-3 LMV acknowledges support by the German Academic Scholarship Foundation (Studienstiftung des deutschen Volkes) and the Marianne-Plehn-Program of the Elite Network of Bavaria. LC and ABW acknowledge support from the Australian Research Council Discovery Project funding scheme (DP210100337) J.F-B acknowledges support from the PID2022-140869NB-I00 grant from the Spanish Ministry of Science and Innovation. MM acknowledges support from the UK Science and Technology Facilities Council through grant ST/Y002490/1.

Austrian Fields of Science 2012

103003 Astronomy
103004 Astrophysics

Keywords

galaxies: bulges
galaxies: evolution
galaxies: general
galaxies: kinematics and dynamics
galaxies: structure

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10.1051/0004-6361/202452891Licence: CC BY 4.0

Cite this

Fraser-McKelvie, A., van de Sande, J., Gadotti, D. A., Emsellem, E., Brown, T., Fisher, D. B., Martig, M., Bureau, M., Gerhard, O., Battisti, A. J., Bland-Hawthorn, J., Boecker, A., Catinella, B., Combes, F., Cortese, L., Croom, S. M., Davis, T. A., Falcón-Barroso, J., Fragkoudi, F., ... Watts, A. B. (2025). The GECKOS survey: Identifying kinematic sub-structures in edge-on galaxies. Astronomy and Astrophysics, 700, Article A237. https://doi.org/10.1051/0004-6361/202452891

@article{eb4df07f2d90455aa62397a121c1cb0b,

title = "The GECKOS survey: Identifying kinematic sub-structures in edge-on galaxies",

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 nGIST analysis pipeline, we derived the mean luminosity-weighted line-of-sight stellar velocity (V★), velocity dispersion (σ★), skew (h3), and kurtosis (h4) for the sample, and examined 2D maps and 1D line profiles. Common clear kinematic signatures were observed: all galaxies display h3 – 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 h3–V★ profile anti-correlations, 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, 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 nGIST 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.",

keywords = "galaxies: bulges, galaxies: evolution, galaxies: general, galaxies: kinematics and dynamics, galaxies: structure",

author = "A. Fraser-McKelvie and \{van de Sande\}, J. and Gadotti, \{D. A.\} and E. Emsellem and T. Brown and Fisher, \{D. B.\} and M. Martig and M. Bureau and O. Gerhard and Battisti, \{A. J.\} and J. Bland-Hawthorn and A. Boecker and B. Catinella and F. Combes and L. Cortese and Croom, \{S. M.\} and Davis, \{T. A.\} and J. Falc{\'o}n-Barroso and F. Fragkoudi and Freeman, \{K. C.\} and Hayden, \{M. R.\} and R. McDermid and \{Mazzilli Ciraulo\}, B. and Mendel, \{J. T.\} and F. Pinna and A. Poci and Rutherford, \{T. H.\} and \{de S{\'a}-Freitas\}, C. and Silva-Lima, \{L. A.\} and Valenzuela, \{L. M.\} and \{van de Ven\}, G. and Z. Wang and Watts, \{A. B.\}",

note = "Publisher Copyright: {\textcopyright} The Authors 2025.",

year = "2025",

month = aug,

day = "1",

doi = "10.1051/0004-6361/202452891",

language = "English",

volume = "700",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP SCIENCES S A",

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Fraser-McKelvie, A, van de Sande, J, Gadotti, DA, Emsellem, E, Brown, T, Fisher, DB, Martig, M, Bureau, M, Gerhard, O, Battisti, AJ, Bland-Hawthorn, J, Boecker, A, Catinella, B, Combes, F, Cortese, L, Croom, SM, Davis, TA, Falcón-Barroso, J, Fragkoudi, F, Freeman, KC, Hayden, MR, McDermid, R, Mazzilli Ciraulo, B, Mendel, JT, Pinna, F, Poci, A, Rutherford, TH, de Sá-Freitas, C, Silva-Lima, LA, Valenzuela, LM, van de Ven, G, Wang, Z & Watts, AB 2025, 'The GECKOS survey: Identifying kinematic sub-structures in edge-on galaxies', Astronomy and Astrophysics, vol. 700, A237. https://doi.org/10.1051/0004-6361/202452891

TY - JOUR

T1 - The GECKOS survey: Identifying kinematic sub-structures in edge-on galaxies

AU - Fraser-McKelvie, A.

AU - van de Sande, J.

AU - Gadotti, D. A.

AU - Emsellem, E.

AU - Brown, T.

AU - Fisher, D. B.

AU - Martig, M.

AU - Bureau, M.

AU - Gerhard, O.

AU - Battisti, A. J.

AU - Bland-Hawthorn, J.

AU - Boecker, A.

AU - Catinella, B.

AU - Combes, F.

AU - Cortese, L.

AU - Croom, S. M.

AU - Davis, T. A.

AU - Falcón-Barroso, J.

AU - Fragkoudi, F.

AU - Freeman, K. C.

AU - Hayden, M. R.

AU - McDermid, R.

AU - Mazzilli Ciraulo, B.

AU - Mendel, J. T.

AU - Pinna, F.

AU - Poci, A.

AU - Rutherford, T. H.

AU - de Sá-Freitas, C.

AU - Silva-Lima, L. A.

AU - Valenzuela, L. M.

AU - van de Ven, G.

AU - Wang, Z.

AU - Watts, A. B.

PY - 2025/8/1

Y1 - 2025/8/1

N2 - 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 nGIST analysis pipeline, we derived the mean luminosity-weighted line-of-sight stellar velocity (V★), velocity dispersion (σ★), skew (h3), and kurtosis (h4) for the sample, and examined 2D maps and 1D line profiles. Common clear kinematic signatures were observed: all galaxies display h3 – 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 h3–V★ profile anti-correlations, 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, 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 nGIST 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.

AB - 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 nGIST analysis pipeline, we derived the mean luminosity-weighted line-of-sight stellar velocity (V★), velocity dispersion (σ★), skew (h3), and kurtosis (h4) for the sample, and examined 2D maps and 1D line profiles. Common clear kinematic signatures were observed: all galaxies display h3 – 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 h3–V★ profile anti-correlations, 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, 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 nGIST 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.

KW - galaxies: bulges

KW - galaxies: evolution

KW - galaxies: general

KW - galaxies: kinematics and dynamics

KW - galaxies: structure

UR - https://www.scopus.com/pages/publications/105014765227

UR - https://telbib.eso.org/detail.php?bibcode=2025A%26A...700A.237F

U2 - 10.1051/0004-6361/202452891

DO - 10.1051/0004-6361/202452891

M3 - Article

AN - SCOPUS:105014765227

SN - 0004-6361

VL - 700

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

M1 - A237

ER -

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

Abstract

Funding

Austrian Fields of Science 2012

Keywords

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