EDP Sciences
Free access
Issue
A&A
Volume 406, Number 2, August I 2003
Page(s) 493 - 503
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20030615


A&A 406, 493-503 (2003)
DOI: 10.1051/0004-6361:20030615

An H $\alpha$ 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?
J. Rossa1, 2 and R.-J. Dettmar1

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 (Present address)

(Received 28 January 2003 / Accepted 15 April 2003 )

Abstract
In a series of two papers we present results of a new H $\alpha$ 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 $\vert z\vert\sim1{-}2$ kpc. Individual filaments can be traced out to $\vert z\vert\leq6$ kpc in a few cases. We find a good correlation between the FIR flux ratio ( S60/S100) and the SFR per unit area ( $L_{\rm FIR}/D^2_{25}$), 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 S60/S100 values, at which extended emission has been detected, was derived, which amounts to $\dot{E}_{\rm A25}^{\rm {thres}} =
(3.2\pm0.5)\times10^{40}\rm {\,erg\,s^{-1}\,kpc^{-2}}$ . There are galaxies where extraplanar emission was detected at smaller values of $L_{\rm FIR}/D^2_{25}$, 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.


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

Offprint request: J. Rossa, jrossa@stsci.edu

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