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Astron. Astrophys. 359, 433-446 (2000)

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

J. Rossa and R.-J. Dettmar

Astronomisches Institut der Ruhr-Universität Bochum, 44780 Bochum, Germany

Received 21 October 1999 / Accepted 20 April 2000


We present narrowband H[FORMULA] 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 H[FORMULA] images reach values of [FORMULA] 2 kpc above the galactic plane. The derived star formation rates (SFRs) from the H[FORMULA] flux of the studied galaxies range from [FORMULA], 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 [FORMULA] versus [FORMULA] in this diagram. We compare the positions of the non-starburst galaxies with starburst galaxies, since these galaxies populate distinct positions in these diagrams.

Key words: galaxies: halos – galaxies: spiral – galaxies: starburst – galaxies: ISM – galaxies: structure

* Based on observations collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: jrossa@astro.ruhr-uni-bochum.de

© European Southern Observatory (ESO) 2000

Online publication: July 7, 2000