Investigation of clusters of galaxies II. A two colour photometry for the cluster Abell 1795
Abstract: A photographic photometry in B and V was performed for the cD cluster of galaxies A 1795 which is located near the north galactic pole. Our catalogue contains 721 galaxies in a field of 1.6 0" around thecluster center.Eine photographische Photometrie in B and V wurde fur den cD-Haufen A 1795 durchgefuhrt. Dieser Haufen liegt in der N&he des galaktischen Nordpols. Unser Katalog enthalt 721 Galaxien in einem Gebiet von 1.6 0" um das Haufenzentrum.Key words: clusters of galaxies -photometry IntroductionThe cluste… Show more
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Cited by 5 publications
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We compiled informations with respect to optical structures, X-ray structures, cooling flow properties, and X-ray luminosities, respectively, for 342 nearby northern Abell clusters with central dominant galaxies.Key words: galaxy clusters -dominant galaxies -cooling flows AAA subject classification: 160 The existence of central dominant galaxies in clusters is a well-known phenomenon. The percentage of galaxy clusters with such galaxies or objects which are in an embryonic state of a cD galaxy is presumably higher by far than usually thought today. The investigation of the evolution of cD clusters and the formation of their dominant galaxies may provide a key for the understanding of the evolution of galaxy clusters at all.The most promising scenarios for the formation of central dominant galaxies in clusters are growth by cooling This catalogue presents a compilation of results with respect to the structures of galaxy clusters with central dominant galaxies and z 5 0.1 deduced from the optical and X-ray observations given in the literature. On the other hand it contains all the available data with respect to X-ray luminosities and estimated accretion rates of cooling flows for these clusters. It is a first step to collect all the available data to discuss the evolution of clusters and their central dominant galaxies. Normally, galaxy clusters are characterized by the BM types I, 11, and I11 or by the RS types cD, B, L, C, F, and I. Correlations of the physical properties of clusters (e.g. radial luminosity segregation, morphological segregation, X-ray emission, accretion rate of a connected cooling flow) in comparison with these morphological cluster types are expected. But many authors find only marginal evidence for such correlations. Sometimes the lack of any clear correlation is explained by selection effects. But we should wonder, if the above given morphological types are an unambiguous expression of the physical evolutionary stages of galaxy clusters. Perhaps we should try to find new criterions for the characterization of galaxy clusters.In this paper we compiled optical and X-ray data for 342 galaxy clusters with central dominant galaxies and with z 5 0.1. From the catalogue of morphological properties of galaxy clusters by Struble and Rood (1987) we found that nearly 90 percent of the objects contain brightest cluster members of the morphological types cD, gE, E, B, SO, b, and t. According to recent results of some authors (e.g. Capaccioli et al. 1990, Michard and Marchal 1994), SO galaxies should not be considered as a seperated class of objects. Rather we should consider a continuity between ellipticals and SO galaxies. Therefore, we have to consider the brightest cluster members of the different morphological types as different evolutionary stages of central dominant galaxies. Because of the high percentage the existence of central dominant galaxies in clusters seems to be the rule and not the exception.An essential aspect of cluster evolution seems to be the fact that dominant galaxies occur fre...
We compiled informations with respect to optical structures, X-ray structures, cooling flow properties, and X-ray luminosities, respectively, for 342 nearby northern Abell clusters with central dominant galaxies.Key words: galaxy clusters -dominant galaxies -cooling flows AAA subject classification: 160 The existence of central dominant galaxies in clusters is a well-known phenomenon. The percentage of galaxy clusters with such galaxies or objects which are in an embryonic state of a cD galaxy is presumably higher by far than usually thought today. The investigation of the evolution of cD clusters and the formation of their dominant galaxies may provide a key for the understanding of the evolution of galaxy clusters at all.The most promising scenarios for the formation of central dominant galaxies in clusters are growth by cooling This catalogue presents a compilation of results with respect to the structures of galaxy clusters with central dominant galaxies and z 5 0.1 deduced from the optical and X-ray observations given in the literature. On the other hand it contains all the available data with respect to X-ray luminosities and estimated accretion rates of cooling flows for these clusters. It is a first step to collect all the available data to discuss the evolution of clusters and their central dominant galaxies. Normally, galaxy clusters are characterized by the BM types I, 11, and I11 or by the RS types cD, B, L, C, F, and I. Correlations of the physical properties of clusters (e.g. radial luminosity segregation, morphological segregation, X-ray emission, accretion rate of a connected cooling flow) in comparison with these morphological cluster types are expected. But many authors find only marginal evidence for such correlations. Sometimes the lack of any clear correlation is explained by selection effects. But we should wonder, if the above given morphological types are an unambiguous expression of the physical evolutionary stages of galaxy clusters. Perhaps we should try to find new criterions for the characterization of galaxy clusters.In this paper we compiled optical and X-ray data for 342 galaxy clusters with central dominant galaxies and with z 5 0.1. From the catalogue of morphological properties of galaxy clusters by Struble and Rood (1987) we found that nearly 90 percent of the objects contain brightest cluster members of the morphological types cD, gE, E, B, SO, b, and t. According to recent results of some authors (e.g. Capaccioli et al. 1990, Michard and Marchal 1994), SO galaxies should not be considered as a seperated class of objects. Rather we should consider a continuity between ellipticals and SO galaxies. Therefore, we have to consider the brightest cluster members of the different morphological types as different evolutionary stages of central dominant galaxies. Because of the high percentage the existence of central dominant galaxies in clusters seems to be the rule and not the exception.An essential aspect of cluster evolution seems to be the fact that dominant galaxies occur fre...
The structure of the centre of the galaxy cluster A 1795 and its surroundings, representing different cluster components, has been investigated in several wavelength ranges. A preferred orientation deviating about 10 -20" from the north-south direction has been found for all cluster components. The orientation of the central cD galaxy is in good agreement with this direction, too. There seem to exist hints for antisegregation in luminosity as well as for colour segregation.Key words: clusters of galaxies -Abell 1795: photometry -structure A A A subject classification: 160 IntroductionThe galaxy cluster Abell 1795 is one of the most interesting clusters of galaxies. It is a cD cluster with an extremely dominant central galaxy classified as BM-type I and Abell richness class 2. A total cluster population N = 115, a redshift z = 0.062 and a radial velocity dispersion or = 821 km s K 1 are given by STRUBLE and ROOD (1982) on the basis of 20 redshift measurements. HILL et al. (1988) published redshifts of 41 cluster members with 6, = 838 km s K 1 and after a correction for relativistic effects according to DANEsEet al. (1980) with or = 786 km s-'. STRUBLE and ROOD (1982) obtained a value 20 arcmin for the total cluster radius and determined the morphological type of the 2nd and 3rd brightest galaxy as SO. Abell 1795 is an amazingly strong X-ray source (MUSHOTSKY 1984) with a smoothed X-ray distribution centered at the cD galaxy (JONES et al. 1979). From this observation and from its strong Ha emission (HECKMAN 1981, VAN BREUGEL et al. 1984) the cD galaxy was recognized to be an extremely strong accretor of cooling gas. The accretion rate amounts to 400 -480 solar masses per year (MUSHOTSKY and SZYMKOWIAK 1988).There appears to be a correlation between the X-ray luminosity and the velocity dispersion of clusters of galaxies, L, z o : (SOLINGER and TUCKER 1972). With the enlargement of the sample of X-ray clusters an increasing scatter about the assumed correlation becomes obvious, however, the basic relationship remains the same (QUINTANA and MELNICK 1982). Hence, the extreme excess of the central X-ray emission of A 1795 above the basic relationship (similar to SC 0316, A 1904, Coma, A 2142, A 262, and A 119) is of special interest.Another point of interest is the same orientation of the cD galaxy and the X-ray emission as discussed by BAIER et al. The formation of cD galaxies at the centres of galaxy clusters is yet an unsolved problem. Several scenarios were suggested, the most promising ones are galaxy cannibalism (HAUSMANN and OSTRIKER 1978) or growth by cooling flow (MUSHOTSKY et al. 1981).In this connection it is remarkable that the presence or absence of a cD galaxy does not depend on cluster properties (MERRIT 1985). cD galaxies appear with nearly equal frequency in clusters of all richness classes and velocity dispersions and even in very poor clusters. They can be observed at a local density peak within a cluster, too. Besides, approximately 25 -50% of all cD galaxies have multiple nuclei , seeming to be ...
We investigate current problems connected with the formation of cD galaxies. The subject of the present paper is to compare internal properties of the cD galaxy Zw162010 with cluster properties of Abell 1795. This consideration is a first attempt to find commonly valid essential correlations between peculiarities of brightest cluster members as structures and active phenomena and global cluster properties as for instance galaxy populations and concentration degrees. The colours, the X-ray emission, and the velocity of the cD galaxy are used to discuss the obvious influence of the environment on the evolution of the active nucleus. In a second paper (Kirchner et al. 1992) the radio structure is used to investigate the influence of the surrounding cluster medium onto the development of the active nucleus. Furtheron, various jet ejection scenarios will be quantitatively examined.Wir betrachten aktuelle Probleme, die mit der Bildung von zentralen, dominierenden (cD) Galaxien in Haufen verbunden sind. Der Gegenstand des vorliegenden ersten Teils einer zweiteiligen Artikelfolge ist es, interne Eigenschaften der cDGalaxie Zw162010 aus Abell 1795 in Beziehung zu setzen mit den betreffenden Haufeneigenschaften. Die Betrachtung ist ein erster Versuch, wesentliche Korrelationen zwischen Besonderheiten der hellsten Mitglieder von Haufen wie Strukturen und aktiven Phanomenen einerseits und globalen Haufeneigenschaften wie z.B. Galaxienpopulationen und Konzentrationsgraden andererseits zu finden. Anhand der Farbe sowie der Rontgenemission wird der Einflufi der Umgebung auf die Evolution des aktiven Galaxienkerns untersucht. In einem zweiten Teil dieser Arbeit (Kirchner et al. 1992) wird die Radio-Struktur der cD-Galaxie benutzt werden, um den offenbaren Einflufl des umgebenden Haufen-Mediums auf die Entwicklung des aktiven Kerns zu untersuchen. Weiterhin werden verschiedene mogliche Jet-Auswurf-Szenarien quantitativ untersucht.Key words: galaxy cluster -cD galaxy -Abell 1795 -Zw162010 A A A subject clossificatzon: 160 IntroductionIn o u r previous paper (Baier et al. 1990) we outlined t h e current problems connected with the formation of c D galaxies. T h e most promising scenarios for their formation a r e galaxy cannibalism (merger scenario) (Hausman a n d Ostriker 1978, Ostriker a n d Tkemaine 1975, W h i t e 1976) a n d growing b y cooling flow (Mushotsky et al. 1981, Silk 1976.T h e merger scenario c a n be divided i n a "strong" a n d a "weak" merger theory. The strong theory says, that the c D galaxies were formed i n clusters within the Hubble t i m e without a n y progenitor, which is in contrast t o t h e weak theory that promotes a massive progenitor of the c D in t h e early universe. In both scenarios a c D galaxy evolves by merging of cluster galaxies. In t h e "weak" theory this process is more effective d u e to the greater dynamical friction which results in a faster orbital decay of cluster galaxies. The merging process of galaxies is a very effective one i n small groups resp. subgroups of galaxy clusters....
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