Published in Astronomy & Astrophysics, Vol. 406, p. 505-525 2003.

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

II. The Halpha survey atlas and catalog

J. Rossa ** 1,2 and R.-J. Dettmar 1

1 Astronomisches Institut, Ruhr-Universitát Bochum, D-44780 Bochum, Germany
E-mail :,

2 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, U.S.A. (present address)

Abstract. In this second paper on the investigation of extraplanar diffuse ionized gas in nearby edge-on spiral galaxies we present the actual results of the individual galaxies of our Halpha imaging survey. A grand total of 74 galaxies have been studied, including the 9 galaxies of a recently studied sub-sample (Rossa & Dettmar, 2000). 40.5% of all studied galaxies reveal extraplanar diffuse ionized gas, whereas in 59.5% of the survey galaxies no extraplanar diffuse ionized gas could be detected. The average distances of this extended emission above the galactic midplane range from 1-2 kpc, while individual filaments in a few galaxies reach distances of up to | z| ~ 6 kpc. In several cases a pervasive layer of ionized gas was detected, similar to the Reynolds layer in our Milky Way, while other galaxies reveal only extended emission locally. The morphology of the diffuse ionized gas is discussed for each galaxy and is compared with observations of other important ISM constituents in the context of the disk-halo connection, in those cases where published results were available. Furthermore, we present the distribution of extraplanar dust in these galaxies, based on an analysis of the unsharp-masked R-band images. The results are compared with the distribution of the diffuse ionized gas.

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

Table of Contents


Halpha observations
Halpha observations
Data reduction and analysis

General results
Results and notes on selected galaxies
Halpha sensitivities and error budgets of the continuum subtraction





* Based on observations collected at the European Southern Observatory, Chile (ESO No. 63.N-0070, ESO No. 64.N-0034, ESO No. 65.N.-0002). Figures 22-54 are only available in electronic form at

** Visiting Astronomer, German-Spanish Astronomical Centre, Calar Alto, operated by the Max-Planck-Institute for Astronomy, Heidelberg, jointly with the Spanish National Commission for Astronomy.