The GECKOS survey: The formation history of a barred galaxy via structural decomposition and spatially resolved spectroscopy

¹ European Southern Observatory, Karl-Schwarzschild-Straße 2, Garching 85748, Germany
² Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
³ Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁴ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago 19001, Chile
⁵ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁶ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁷ Cardiff Hub for Astrophysics Research & Technology, School of Physics & Astronomy, Cardiff University, Queens Buildings, Cardiff CF24 3AA, UK
⁸ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218 Hawthorn VIC 3122, Australia
⁹ Homer L. Dodge Department of Physics & Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK 73019, USA
¹⁰ School of Physics, University of New South Wales, NSW 2052, Australia
¹¹ International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia, M468, 35 Stirling Highway, Crawley, WA 6009, Australia

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 September 2025
Accepted: 1 November 2025

Abstract

Disentangling the (co-)evolution of individual galaxy structural components remains a difficult task, owing to the inability to cleanly isolate light from spatially overlapping components. In this pilot study of PGC 044931, observed as part of the GECKOS survey, we utilised a VIRCAM H-band image to decompose the galaxy into five photometric components, three of which dominate by contributing more than 50% of light in specific regions, namely, a main disc, a boxy-peanut bulge, and a nuclear disc. When mapping the photometric decompositions onto MUSE observations, we found remarkably good separation in stellar kinematic space. All three structures occupy unique locations in the parameter space of the ratio of the light-weighted stellar line-of-sight mean velocity and velocity dispersion (V_★/σ_★) and the high-order stellar skew (h₃). These clear and distinct kinematic behaviours allowed us to make inferences about the formation histories of the individual components from observations of the mean stellar ages and metallicities of the three components. A clear story emerged: the main disc was built over a sustained and extended star formation phase, possibly partly fuelled by gas from a low-metallicity reservoir. Early on, that disc formed a bar that buckled and subsequently formed a nuclear disc in multiple and enriched star-formation episodes. This result is an example of how careful photometric decompositions combined with spatially well-resolved stellar kinematic information can help separate age-metallicity relations of different components and therefore disentangle the formation history of a galaxy. The results of this pilot study can be extended to a differential study of all GECKOS survey galaxies to assert the true diversity of Milky Way-like galaxies.