An Hα survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge-on spiral galaxies^*

I. How common are gaseous halos among non-starburst galaxies?

¹ Astronomisches Institut, Ruhr-Universität Bochum, 44780 Bochum, Germany e-mail: dettmar@astro.ruhr-uni-bochum.de
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA ()

Corresponding author: J. Rossa, jrossa@stsci.edu

Received: 28 January 2003
Accepted: 15 April 2003

Abstract

In a series of two papers we present results of a new Hα imaging survey, aiming at the detection of extraplanar diffuse ionized gas in halos of late-type spiral galaxies. We have investigated a sample of 74 nearby edge-on spirals, covering the northern and southern hemisphere. In 30 galaxies we detected extraplanar diffuse emission at mean distances of  kpc. Individual filaments can be traced out to  kpc in a few cases. We find a good correlation between the FIR flux ratio () and the SFR per unit area (), based on the detections/non-detections. This is actually valid for starburst, normal and for quiescent galaxies. A minimal SFR per unit area for the lowest values, at which extended emission has been detected, was derived, which amounts to . There are galaxies where extraplanar emission was detected at smaller values of , however, only in combination with a significantly enhanced dust temperature. The results corroborate the general view that the gaseous halos are a direct consequence of SF activity in the underlying galactic disk.