Extraplanar emission in isolated edge-on late-type galaxies – II. The Hα kinematics

ABSTRACT Isolated galaxies are rare yet invaluable for studying secular evolution, as their physical properties can remain largely unaffected by external influences for several billion years, primarily shaped by internal evolutionary processes. This study focuses on a representative sample of nearly edge-on ($i\ge 80^{\circ }$) late-type galaxies selected from the Catalogue of Isolated Galaxies. We analyse the H $\alpha$ kinematics derived from Fabry–Perot data and integrate these findings with a comprehensive examination of the ultraviolet, optical, and far-infrared properties of these galaxies to study their dynamic evolutionary processes. We investigate the individual kinematics by computing rotation curves and dynamical masses for each galaxy in the sample. The accuracy of our kinematic results is confirmed through comparisons with ${\rm H\, {\small I}}$ data and by applying the B- and K-band Tully–Fisher relationships. Among the galaxies studied, we observed a rotational lag along the z-axis in half of the total sample (seven out of 14 cases), with an average lag ($\Delta V/\Delta z=32.0\pm 10.6$ km s$^{-1}$ kpc$^{-1}$) consistent with previous research findings. Notably, not all galaxies exhibiting measurable lag display morphological extraplanar components, leading us to conclude that this cannot serve as a definitive marker for the extraplanar diffuse ionized gas component. While we found no significant correlations between rotation lag and overall galaxy properties, there seems to be a potential correlation with tidal strength. Based on the kinematic characteristics observed in our sample, we suggest that the extended disc gas likely originates from interactions with the circumgalactic medium rather than arising internally within the galaxies themselves.