Extraplanar diffuse ionized gas in a small sample of nearby edge-on galaxies

We present narrowband Hα imaging data of a small survey of nearby edge-on spiral galaxies, aiming at the detection of ‘extraplanar’ diffuse ionized gas (DIG). A few of our studied edge–on spirals show signs of disk–halo interaction (DHI), where extended line emission far above the galactic plane of these galaxies is detected. In some cases an extraplanar diffuse ionized gas (eDIG) layer is discovered, e.g., NGC4634, NGC 3044, while other galaxies show only filamentary features reaching into the halo (e.g., IC 2531) and some galaxies show no sign of eDIG at all. The extraplanar distances of the DIG layer in our narrowband Hα images reach values of z ≤ 2 kpc above the galactic plane. The derived star formation rates (SFRs) from the Hα flux of the studied galaxies range from 0.05 − 0.7M yr−1, neglecting a correction for internal absorption. The variation of the SFR values among our sample galaxies reflects the diversity of star formation within this sample. A diagnostic diagram is introduced, which allows to predict the existence of gas halos in ‘quiescent’ galaxies based on the ratio S60/S100 versus LFIR/D 25 in this diagram. We compare the positions of the non–starburst galaxies with starburst galaxies, since these galaxies populate distinct positions in these diagrams.