The GECKOS Survey: extraplanar ionized gas in star-forming galaxies from eDIG to galaxy-scale winds

Elliott, R, Fisher, DB, Mazzilli Ciraulo, B, Fraser-McKelvie, A, Hayden, MR, Martig, M ORCID: 0000-0001-5454-1492, van de Sande, J, Battisti, AJ, Bland-Hawthorn, J, Bolatto, AD, Brown, TH, Catinella, B, Combes, F, Cortese, L, Davis, TA, Emsellem, E, Gadotti, DA, Pinna, F, Puzia, TH, Silva-Lima, LA et al (2026) The GECKOS Survey: extraplanar ionized gas in star-forming galaxies from eDIG to galaxy-scale winds. Monthly Notices of the Royal Astronomical Society, 548 (3). ISSN 0035-8711

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Abstract

We map the extraplanar gas, with (Formula presented) 50–200 pc resolution, in nine star-forming galaxies using Multi-Unit Spectroscopic Explorer (MUSE) observations from the GECKOS VLT Large Programme targeting edge-on galaxies with similar stellar mass as the Milky Way. The narrow range in stellar mass ((Formula presented)  dex) of the GECKOS sample makes it ideal for studying trends with star formation rate (SFR). We find strong extraplanar emission reaching (Formula presented) 2-8 kpc from the disc mid-plane in all targets with (Formula presented) 1 M(Formula presented)  yr(Formula presented). Targets with SFR (Formula presented) 5 M(Formula presented)  yr(Formula presented) have brighter, more extended H(Formula presented) emission compared to lower SFR targets. In high-SFR systems, the gas velocity dispersion ((Formula presented) ) shows a biconical morphology, consistent with the expectation of outflows. This agrees with previous works suggesting high velocity dispersion in a biconical shape is a good means to identify outflows. We find mixed results using line diagnostics ([O iii](Formula presented) /H (Formula presented) –[N ii]/H (Formula presented) and (Formula presented) –[S ii]/H (Formula presented) ) to spatially resolve ionization mechanisms across the extraplanar gas. The highest [N ii]/H (Formula presented) are found in the extraplanar gas of the highest SFR systems, yet main-sequence galaxies have the highest [O iii]/H (Formula presented). While the morphology of [N ii]/H (Formula presented) may be useful to identify outflows, the absolute value of the line ratio alone may not distinguish strong outflows from extraplanar gas of main-sequence galaxies. The ubiquitous extraplanar emission can be interpreted as the result of feedback, in the form of large-scale winds for starbursts or smaller-scale galactic fountains for main-sequence galaxies. Moreover, shock-heating may ionise gas at the interface of the disc and the circumgalactic medium, independent of the source of the gas.

Item Type:	Article
Uncontrolled Keywords:	galaxies: ISM; galaxies: spiral; galaxies: starburst; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	25 March 2026
Date of first compliant Open Access:	15 September 2026
Date Deposited:	15 Sep 2026 09:27
Last Modified:	15 Sep 2026 09:27
DOI or ID number:	10.1093/mnras/stag672
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29423

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