Bidimensional Exploration of the warm-Temperature Ionised gaS (BETIS) I. Showcase sample and first results

Abstract

We present the Bidimensional Exploration of the warm-Temperature Ionised gaS (BETIS) project, designed for the spatial and spectral study of the diffuse ionised gas (DIG) in a selection of nearby spiral galaxies observed with the MUSE integral-field spectrograph. Our primary objective is to investigate the various ionisation mechanisms at play within the DIG. We analysed the distribution of high- and low-ionisation species in the optical spectra of the sample on a spatially resolved basis. We introduced a new methodology for spectroscopically defining the DIG, optimised for galaxies of different resolutions. We also examined the suitability of using Ha equivalent width (EWha) as a proxy for defining the DIG and its associated ionisation regime. The average radial distribution of the main line ratios are enhanced in the DIG. It follows similar trends between the DIG regime and the HII regions, as well as the Ha surface brightness, indicating a correlation between the ionisation of these species in both the DIG and the HII regions. The DIG loci in diagnostic diagrams are found within the line ratios that correspond to photoionisation due to the star formation. There is a noticeable offset correspondent to fast shocks. However, an individual diagnosis performed for each galaxy reveals that all the DIG in these galaxies can be attributed to photoionisation from star formation. The offset is primarily due to the contribution of Seyfert galaxies in our sample, which is closely aligned with models of ionisation from fast shocks and galactic outflows, thus mimicking the DIG emission. Our results indicate that galaxies exhibiting active galactic nucleus activity should be considered separately when conducting a general analysis of the DIG ionisation mechanisms, since this emission is indistinguishable from high-excitation DIG.

21 pages, 15 figures, A&A accepted

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Cited by in corpus (3)

• Bidimensional Exploration of the warm-Temperature Ionised gaS (BETIS) II. Revisiting the ionisation mechanism of the extraplanar diffuse ionised gas
• HeII emitters at cosmic noon and beyond. Characterising the HeII λ1640 emission with MUSE and JWST/NIRSpec
• Temperature based radial metallicity gradients in nearby galaxies