Astronomy & Astrophysics manuscript no. (will be inserted by hand later) An Hα survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge–on spiral galaxies ⋆ II. The Hα survey atlas and catalog J. Rossa ⋆⋆1,2 and R.–J. Dettmar1 1 Astronomisches Institut, Ruhr–Universit¨at Bochum, D–44780 Bochum, Germany e-mail: [email protected], [email protected] 2 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, U.S.A. (present address) Received 14 February 2003 / Accepted 6 May 2003 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 Hα 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 1. Introduction of the star formation activity, both on local and global arXiv:astro-ph/0305472v1 23 May 2003 scales (Rand 1996; Rossa & Dettmar 2000). To answer Our current knowledge of the morphology of the ex- this question a systematic investigation is obligatory. We traplanar diffuse ionized gas (eDIG) in normal (non– have therefore conducted, for the first time, a large sur- starburst) edge–on spiral galaxies rests on a few in- vey of nearby non–starburst edge–on spiral galaxies, aim- vestigations of small galaxy samples (Pildis et al. 1994; ing at a quantitative morphological study of gaseous ha- Rand 1996; Hoopes et al. 1999; Rossa & Dettmar 2000), los, based on the broad coverage of the strength of SF as well as on some additional studies of individual galax- activity in the underlying galaxy disks (i.e. broad cover- ies (e.g., Dettmar 1990; Rand et al. 1992; Ferguson et al. age of LFIR) of these galaxies. We present the observed 1996; Domg¨orgen & Dettmar 1997). There have been a morphological results, based on the Hα imaging obser- few galaxies studied during the last decade, however, the vations, and describe the derived DIG characteristics for question was raised, whether or not the presence of eDIG each galaxy in this paper in greater detail. For informa- is a common phenomenon among all types of galaxies, or tion on the scientific background on eDIG and its detec- whether it is indeed a direct consequence of the strength tion in external galaxies we refer the reader to our previ- Send offprint requests to: J. Rossa ous works (Rossa & Dettmar 2000, 2003), and references ⋆ Based on observations collected at the European Southern therein and to some older review articles (Dettmar 1992; Observatory, Chile (ESO No. 63.N–0070, ESO No. 64.N–0034, Dahlem 1997) for a more detailed overview on this topic. ESO No. 65.N.–0002). Figures 22-54 are only available in elec- tronic form at http://www.edpsciences.org The current paper is structured as follows. In Sect. 2 ⋆⋆ Visiting Astronomer, German–Spanish Astronomical we present some details on the observations and data re- Centre, Calar Alto, operated by the Max–Planck–Institute duction procedures. In Sect. 3 we show the actual results for Astronomy, Heidelberg, jointly with the Spanish National for the galaxies, while in Sect. 4 we discuss the extraplanar Commission for Astronomy. dust. Then the atlas is presented (available only electron- 2 J. Rossa and R.–J. Dettmar: An Hα survey aiming at the detection of eDIG in edge–on spiral galaxies ically at EDP Sciences), where we display two galaxies on each page. Each of the two columns per page consists of the R–band (top), the unsharp–masked R–band (mid- dle), and the continuum subtracted Hα image (bottom). Finally, in Sect. 5 we summarize briefly the results. 2. Observations and data reduction 2.1. Hα observations The edge–on spiral galaxies, which form the basis of this Hα survey, have been observed in five individual observing runs between 1999 and 2000. The northern hemisphere objects (Runs NH–1, NH–2) have been ob- served with the CAHA1 2.2 m telescope at the Calar Alto Observatory in southern Spain, and the southern hemi- Fig. 1. Transmission curves for the ESO and Calar Alto Hα fil- sphere objects (Runs SH–1, SH–2, SH–3) have been ob- ters (ESO #693, #697, #701 and CA #658/10, CA #665/17), served with the Danish 1.54m telescope at the European respectively. The plot has been generated in the MIDAS envi- Southern Observatory at La Silla/Chile (see Table 1 for a ronment with the use of the implemented ESO filter and edited CAHA filter table–files. summary of the individual observing runs). Six additional targets, that were selected on the basis of our selection criteria, have also been included into this survey. These were galaxies, already observed several years ago in past was a LORAL/LESSER 2k × 2 k chip with a pixel size of observing runs, or that were at our disposal, so we did not 15µm. The pixel scale was 0′′. 39 pix−1, and the maximum have to re–observe them (Runs SH–a, SH–b, SH–c). The field of view (fov) was 13.′7 × 13.′7. Due to vignetting ef- basic galaxy properties, including the coordinates, galaxy fects at the borders of the filters we have used only the types, distances, radial velocities, sizes, inclinations, and inner 1601 × 1601 pixels of the CCD chip in most cases, magnitudes, are listed in Table 2. yielding a fov of 10.′4 × 10.′4. The used Hα filters were the ESO #693, #697, and #701 filters with a ∆λ = 62.1 A,˚ 61.6 A,˚ and 63.1 A,˚ respectively. The broad–band observa- Table 1. Individual observing runs for the new Hα survey tions, to be used for the continuum subtraction, have been acquired through the ESO #452 (Bessel R) filter, which Run No. Dates Telescope has a ∆λ =1647 A.˚ Instrumental parameters for six addi- NH–1 19–22/02/1999 CAHA2.2 tional objects can be found elsewhere (Rossa & Dettmar NH–2 08–13/08/1999 CAHA2.2 2000). The Hα transmission curves of the filters, which SH–1 07–10/07/1999 DAN1.54 have been used for this survey, are shown in Fig. 1. A SH–2 09–13/11/1999 DAN1.54 SH–3 29/07–01/08/2000 DAN1.54 journal of observations for our galaxies is given in Table 3. SH–a 22/02/1993 ESO2.2 SH–b 07–08/05/1991 NTT 2.2. Data reduction and analysis SH–c 10/02/1995 NTT The data reduction has been performed in the usual manner including bias level correction, flat–fielding, back- ground correction, registering of the stars (alignment of The observations for the northern hemisphere galax- the R–band image with respect to the Hα image), scaling ies have been performed with CAFOS2 in direct imaging of the R–band image, and final continuum subtraction. In mode, attached to the CAHA 2.2 m telescope. The used almost all cases the Hα images (split into two individual CCD chip was a 2048 × 2048 pixel SITe#1d, with a pixel exposures for cosmic ray removal) have been combined. size of 24µm. The pixel scale was 0′′. 53 pix−1, and the re- All these reduction steps have been performed using var- sulting field of view was 18.′1 × 18.′1. The used Hα filters ious IRAF packages. were the CA #658/10 and the CA #665/17 filters with a For the northern survey the bias correction was per- ∆λ = 98 A˚ and 168 A,˚ respectively. The used R–band filter formed by using the IRAF colbias task, taking the in- (Johnson R) was the CA #641/158 with ∆λ = 1575 A.˚ formation of the overscan region into account. This was The southern hemisphere galaxies have been observed appropriate, since the bias exposures showed diagonal with DFOSC3 in imaging mode, attached to the Danish stripes. For the southern hemisphere objects the bias cor- 1.54 m telescope at La Silla/Chile. The used CCD camera rection was done using a masterbias frame (one per night) 1 Centro Astron´omico Hispano Alem´an obtained from median combining individual bias frames 2 Calar Alto Faint Object Spectrograph of each night. The flat–field correction was done using a 3 Danish Faint Object Spectrograph Camera normalized flat–field image created from combining the J. Rossa and R.–J. Dettmar: An Hα survey aiming at the detection of eDIG in edge–on spiral galaxies 3 individual flat–field exposures for each filter separately.