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Astron. Astrophys. 349, 97-107 (1999)

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2. The data

2.1. Optical data

Our optical analysis is based on the following data:

  • Chapman et al. (1988) have observed a list of 74 cluster member galaxies in ABCG 194 (i.e. with velocities in the 4000-6600 km s-1 range), located within a radius of 3o (5.6 Mpc) around the cluster center. The CGH sample is 97% complete for galaxies brighter than B=16.7 in a region of radius R=30 arcmin around the cluster center, and 80% complete for galaxies brighter than B=15.5 in the entire region.

    Out of the 74 galaxies in this sample, 48 and 62 are located within radii of 30 arcmin and 1o of the cluster center respectively. For all these galaxies, CGH give the following data: coordinates, radial velocity, B magnitude, morphological type, major axis position angle and ellipticity.

  • We have added to this sample 22 optically fainter galaxies selected from the CF2+SSRS2 redshift survey, for which Barton et al. (1998) give positions and redshifts (hereafter the BCG sample); these authors determined that the region of 1o radius around the ABCG 194 cluster is 100% complete for galaxies brighter than [FORMULA]. For the three galaxies with numbers 15, 30 and 54 in the CGH list, we take the radial velocity from the Barton et al. (1998) paper, where the error is smaller than in CGH.

  • The coordinates and redshift for an additional (Seyfert) galaxy were taken from Knezek & Bregman (1998).

The total sample therefore includes 97 galaxies located within the following range of positions relative to the cluster center: [FORMULA]X[FORMULA]6480 and [FORMULA]Y[FORMULA]8710 arcsec.

2.2. X-ray data

Our X-ray study is based on a ROSAT PSPC image of ABCG 194 retrieved from the ROSAT data bank; the exposure time was 24482 seconds (P.I. Murray & Stephens). This image was processed with the Snowden software (Snowden et al. 1994). Obviously, this cluster is not a strong X-ray emitter, since in spite of the relatively high exposure time the total amount of counts is 8530, which is small. We show in Fig. 2 a superposition of the optical and X-ray maps, and in Fig. 3 that of the optical and radio maps. Notice that there is a zoom by a factor of [FORMULA]3 between these two images.

[FIGURE] Fig. 1. Positions of the sample galaxies relative to the cluster center. Squares and crosses indicate galaxies from the CGH and BCG samples respectively. The circles have 30 arcmin and 1o radii.

[FIGURE] Fig. 2. Digital Sky Survey image superimposed with ROSAT X-ray image contours (1, 2, 3 and 4 [FORMULA]) superimposed.

[FIGURE] Fig. 3. Digital Sky Survey image superimposed with NVSS radio (1.4 GHz) image contours (from 12 [FORMULA] up by a factor of 2).

In X-rays, the signal to noise ratio is low: we give in Fig. 4 the curves which allow us to obtain the number of pixels above a certain count level. 99% of the pixels contain only 1 or 2 counts (essentially noise) for both clusters; however, there are much more pixels with a large number of counts (essentially signal) in ABCG 85 than in ABCG 194.

[FIGURE] Fig. 4. Percentage of the number of pixels with a count level higher than a given value, in the weak X-ray cluster ABCG 194 (full line) and in the bright X-ray cluster ABCG 85 normalized to the same total number of counts.

2.3. Radio data

In the center of this cluster are located the radiosources 0123-016A and 0123-016B. The "dumbbell" source 0123-016A coincides with two galaxies, one of them being NGC 547 (3C 40), while 0123-016B coincides with NGC 541 (Ledlow & Owen 1995, Edge & Röttgering 1995); NGC 547 and NGC 541 are the first are third magnitude galaxies in the cluster respectively. The radiosource 3C 40 has a "Twin Jet" structure (Burns et al. 1994). The optical disk of NGC 547 is perpendicular to the radio axis (Zirbel & Baum 1998) and its direction coincides with that joining NGC 541 and 547 (Fasano et al. 1996). NGC 541 is a narrow-angle-tailed (NAT) radio galaxy. The direction of the tail coincides with that between NGC 541 and 547 (O'Dea & Owen 1985). According to Brodie et al. (1985) and van Breugel et al. (1985), this radio source may be interacting with Minkowski's object.

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© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999
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