Neutral and Ionised Hydrogen in NGC 4214

Abstract

AbstractIt is not clear at present how the diffuse ionised gas (DIG) component in galaxies is ionised. The leading hypothesis is that ultraviolet photons from star clusters are responsible, but this requires a rather porous interstellar medium if the photons are to travel the large distances (≥ 1 kpc) between the bright clusters and diffuse-emission regions. To examine this hypothesis, we present high-resolution VLA observations of the neutral hydrogen in the Magellanic galaxy NGC 4214, and compare them with an Hα image. The data appear consistent with the idea that enough UV photons escape from supergiant H II regions to ionise the DIG.