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Astron. Astrophys. 343, 760-774 (1999)

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5. Conclusions

The combined large field photographic plate and small field CCD imaging catalogues, coupled with extensive spectroscopic data, have led us to gather one of the largest amounts of data for a single cluster. These data have been used in the present paper to analyze several properties of ABCG 85. Some of these properties have already been discussed in the past by various authors (see Introduction), but the large amount of data now available allows a more refined analysis, leading either to derive new properties or to confirm previous results with a high confidence level.

First, we have compared the distributions of emission line (ELGs) and non-emission line galaxies (NoELGs), and shown that ELGs seem intrinsically fainter than NoELGs, and do not appear as centrally condensed as NoELGs, both spatially and in velocity space. ELGs show an enhancement south of the nucleus, where groups are falling onto the main cluster (as discussed in our previous paper by Durret et al. 1998b). This fits in well with the general view of this cluster: the gas in the galaxies belonging to these groups is expected to be shocked and consequently star formation should be more important in the impact region at the epoch of actual galaxy infall, and less important in the central regions of clusters where star formation appears to be truncated. This has been shown to be the case for two clusters at redshifts 0.2 and 0.4 by Abraham et al. (1996) and Morris et al. (1998). Besides, the cluster analyzed by Abraham et al., ABCG 2390, shows evidence for a subcomponent infalling onto the main cluster, as the south blob is falling onto ABCG 85.

Second, we have analyzed in detail the luminosity function of ABCG 85 in the R band, using a wavelet reconstruction technique. We have shown with a high confidence level that a dip was present at an absolute magnitude [FORMULA]. This feature has also been detected in several other clusters and can be accounted for by the distributions of the various types of galaxies present in the cluster. In this scenario, the dip would correspond to the separation between elliptical and dwarf galaxies.

Third, parametric and non-parametric methods applied to our redshift catalogue have allowed us to derive the dynamical properties of the cluster. We find that the dynamical mass profiles derived from the X-ray gas and galaxy distributions agree if the temperature of the X-ray emitting plasma is about 8 keV. Between 250 and 1000 arcsec, whatever technique we apply (parametric or not), and whatever data we use (X-ray or optical), the slopes of the dynamical mass profiles are the same ([FORMULA]). In this region, both the X-ray plasma and the "gas" of galaxies are isothermal, and the galaxy velocity dispersion is isotropic. If we take into account the temperature gradient of the X-ray gas, the dynamical mass is reduced. If we take into account a possible temperature gradient of the X-ray gas, the `X-ray' dynamical mass is reduced at very large scale but is still comparable to the `optical' dynamical mass in the X-ray emitting region.

Although this paper is the last one of the series on ABCG 85, the analysis of a much larger area in that region of the sky is planned in a near future: we have recently obtained about 300 new redshifts in the direction of ABCG 87 (in collaboration with M. Colless), and have the project of obtaining redshifts for the various clusters and groups aligned along [FORMULA] and in which ABCG 85 seems embedded. We also intend to discuss the large scale structure properties of the universe in the direction of ABCG 85, based on the large scale velocity features of our velocity catalogue.

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999