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?

In a series of two papers we present results of a new Halpha 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 \z\ similar to 1-2 kpc. Individual filaments can be traced out to \z\ less than or equal to 6 kpc in a few cases. We find a good correlation between the FIR flux ratio (S (60)/S (100)) and the SFR per unit area (L-FIR/D-25(2)), 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 S (60)/S (100) values, at which extended emission has been detected, was derived, which amounts to. (E) over dot (thres)(A25) = (3.2 +/- 0.5) x 10(40) erg s(-1) kpc(-2). There are galaxies where extraplanar emission was detected at smaller values of L-FIR/D-25(2), 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.