Abstract We map the extraplanar gas, with ∼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 (±0. 35 dex) of the GECKOS sample makes it ideal for studying trends with star formation rate (SFR). We find strong extraplanar emission reaching ∼2-8 kpc from the disk midplane in all targets with SFR1 M⊙ yr−1. Targets with SFR ≥ 5 M⊙ yr−1 have brighter, more extended Hα emission compared to lower SFR targets. In high-SFR systems, the gas velocity dispersion (σHα) 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 (OIII5007/Hβ - NII/Hα and σHα - SII/Hα) to spatially resolve ionisation mechanisms across the extraplanar gas. The highest NII/Hα are found in the extraplanar gas of the highest SFR systems, yet main-sequence galaxies have the highest OIII/Hβ. While the morphology of NII/Hα 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.
Elliott et al. (Mon,) studied this question.
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