The GECKOS Survey: Extraplanar ionised gas in star-forming galaxies from eDIG to galaxy-scale winds
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| Format: | Preprint |
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2026
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| author | Elliott, R. Fisher, D. B. Ciraulo, B. Mazzilli Fraser-McKelvie, A. Hayden, M. R. Martig, M. van de Sande, J. Battisti, A. J. Bland-Hawthorn, J. Bolatto, A. D. Brown, T. H. Catinella, B. Combes, F. Cortese, L. Davis, T. A. Emsellem, E. Gadotti, D. A. Pinna, F. Puzia, T. H. Silva-Lima, L. A. Valenzuela, L. M. van de Ven, G. |
| author_facet | Elliott, R. Fisher, D. B. Ciraulo, B. Mazzilli Fraser-McKelvie, A. Hayden, M. R. Martig, M. van de Sande, J. Battisti, A. J. Bland-Hawthorn, J. Bolatto, A. D. Brown, T. H. Catinella, B. Combes, F. Cortese, L. Davis, T. A. Emsellem, E. Gadotti, D. A. Pinna, F. Puzia, T. H. Silva-Lima, L. A. Valenzuela, L. M. van de Ven, G. |
| contents | We map the extraplanar gas, with $\sim$50-200 pc resolution, in nine star-forming galaxies using Multi-Unit Spectroscopic Explorer (MUSE) observations from the GECKOS VLT Large Program targeting edge-on galaxies with similar stellar mass as the Milky Way. The narrow range in stellar mass ($\pm0.35$ dex) of the GECKOS sample makes it ideal for studying trends with star formation rate (SFR). We find strong extraplanar emission reaching $\sim$2-8 kpc from the disk midplane in all targets with $\rm{SFR}\geq$1 M$_{\odot}$ yr$^{-1}$. Targets with SFR$\,\geq\,$5 M$_{\odot}$ yr$^{-1}$ have brighter, more extended H$α$ emission compared to lower SFR targets. In high-SFR systems, the gas velocity dispersion ($σ_{\rm Hα}$) 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 ([OIII]$_{5007}$/H$β$ - [NII]/H$α$ and $σ_{\rm Hα}$ - [SII]/H$α$) to spatially resolve ionisation mechanisms across the extraplanar gas. The highest [NII]/H$α$ are the extraplanar gas of the highest SFR systems, yet main-sequence galaxies have the highest [OIII]/H$β$. While the morphology of [NII]/H$α$ 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 disk and the circumgalactic medium, independent of the source of the gas. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_22500 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The GECKOS Survey: Extraplanar ionised gas in star-forming galaxies from eDIG to galaxy-scale winds Elliott, R. Fisher, D. B. Ciraulo, B. Mazzilli Fraser-McKelvie, A. Hayden, M. R. Martig, M. van de Sande, J. Battisti, A. J. Bland-Hawthorn, J. Bolatto, A. D. Brown, T. H. Catinella, B. Combes, F. Cortese, L. Davis, T. A. Emsellem, E. Gadotti, D. A. Pinna, F. Puzia, T. H. Silva-Lima, L. A. Valenzuela, L. M. van de Ven, G. Astrophysics of Galaxies We map the extraplanar gas, with $\sim$50-200 pc resolution, in nine star-forming galaxies using Multi-Unit Spectroscopic Explorer (MUSE) observations from the GECKOS VLT Large Program targeting edge-on galaxies with similar stellar mass as the Milky Way. The narrow range in stellar mass ($\pm0.35$ dex) of the GECKOS sample makes it ideal for studying trends with star formation rate (SFR). We find strong extraplanar emission reaching $\sim$2-8 kpc from the disk midplane in all targets with $\rm{SFR}\geq$1 M$_{\odot}$ yr$^{-1}$. Targets with SFR$\,\geq\,$5 M$_{\odot}$ yr$^{-1}$ have brighter, more extended H$α$ emission compared to lower SFR targets. In high-SFR systems, the gas velocity dispersion ($σ_{\rm Hα}$) 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 ([OIII]$_{5007}$/H$β$ - [NII]/H$α$ and $σ_{\rm Hα}$ - [SII]/H$α$) to spatially resolve ionisation mechanisms across the extraplanar gas. The highest [NII]/H$α$ are the extraplanar gas of the highest SFR systems, yet main-sequence galaxies have the highest [OIII]/H$β$. While the morphology of [NII]/H$α$ 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 disk and the circumgalactic medium, independent of the source of the gas. |
| title | The GECKOS Survey: Extraplanar ionised gas in star-forming galaxies from eDIG to galaxy-scale winds |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2601.22500 |