EXTRAPLANAR EMISSION-LINE GAS IN EDGE-ON GALAXIES

Seven edge-on galaxies were imaged in Halpha in order to determine if extraplanar emission-line gas (as seen in NGC 891) is a common feature of spiral galaxies. Four of the seven are found to have one or two pr ominent filamentary extraplanar structures apiece, with typical filame nt Halpha luminosities of 10(37)-10(38) ergs s-1 and scales of 1-2 kpc . Unlike NGC 891, none of the galaxies has an extensive emission-line halo, to within the sensitivity of the observations, approximately 24 mag per square arcsec in Halpha (equivalent to an emission measure of 19 pc cm-6)-more than 7 times fainter than the diffuse emission of NGC 891.