Elena Panko

ORIENTATION OF BRIGHTER GALAXIES IN NEARBY GALAXY CLUSTERS

A sample of 6188 nearby galaxy structures, complete to rF = 183 and containing at least 10 members each, was the observational basis for an investigation of the alignment of bright galaxies with the major axes for the parent clusters. The distribution of position angles for galaxies within the clusters, specifically the brightest, the second brightest, the third, and the tenth brightest galaxies was tested for isotropy. Galaxy position angles appear to be distributed isotropically, as are the distributions of underlying cluster structure position angles. The characterization of galaxy structures according to richness class also appears to be isotropic. Characterization according to BM types, which are known for 1056 clusters, is more interesting. Only in the case of clusters of BM type I is there an alignment of the brightest cluster member with the major axis of the parent cluster. The effect is observed at the 2 significance level. In other investigated cases the distributions are isotropic. The results confirm the special role of cD galaxies in the origin/evolution of large-scale structures.

THE EVOLUTION OF LOW-REDSHIFT GALAXY STRUCTURES

Ellipticities for 6188 low-redshift (z < 0.18) poor and rich galaxy structures have been examined along with their evolution using an optical observational base that is statistically complete. The shape of each structure projected on the celestial sphere was determined using the covariance ellipse method. Analysis of the data indicates that structure ellipticity changes with redshift, being smaller for nearby objects and greater for those located further away. Such a change is also described better by quadratic or exponential relations than by a simple linear scheme. It is concluded that between redshifts of z = 0.18 and z = 0 we observe the dynamical evolution of galaxy clusters. Such a change in ellipticity with redshift is expected in ΛCDM models.

THE SHAPE OF GALAXY STRUCTURES

An analysis is presented for a statistically complete sample of 547 galaxy structures with z ≤ 0.16, each containing at least 10 objects. The sample was divided according to structure richness, representing 10 richness classes, with the distribution of ellipticities differing among individual classes. Mean ellipticity varies from 0.34 to 0.18, less well populated structures being more elongated that richer ones. Statistics indicate that structures with at least 50 members originate from the same population. The mean redshift of a structure class is a function of richness, with less well populated classes exhibiting greater mean redshifts than richer galaxy clusters. Further analysis reveals a dependence of the ellipticity-redshift correlation on structure richness. Among rich galaxy clusters there is an anti-correlation between the parameters, the strongest correlation occurring for the most poorly populated galaxy classes.

The environmental effects in the origin of angular momenta of galaxies

We study the galaxy alignment in the sample of very rich Abell clusters located in and outside superclusters. The statistically significant difference among investigated samples exists. We found that in contrast to whole sample of cluster, where alignment increase with the cluster richness, the cluster belonging to the superclusters does not show this effect. Moreover, the alignment decreased with the supercluster richness. One should note however that orientations of galaxies in analyzed clusters are not random, both in the case when we analyzed whole sample of the clusters and only clusters belonging to the superclusters. The observed trend, dependence of galaxy alignment on both cluster location and supercluster richness clearly supports the influence of environmental effects to the origin of galaxy angular momenta.

THE ALIGNMENT OF GALAXY STRUCTURES

We analyzed the orientation of the sample of ACO galaxy clusters. We examined the alignment in a subsample of 1056 galaxy structures taken from the Panko–Flin (2006) Catalog with known BM morphological types. We were looking for a correlation between the orientation of the cluster and the positions of neighboring clusters. The Binggeli effect (the excess of small values of the Δθ angles between the direction toward neighboring clusters and the cluster position angle) is observed, having a range up to about 45 h−1 Mpc. The strongest effect was found for elongated BM type I clusters. This is probably connected with the origins of the supergiant galaxy and with cluster formation along a long filament or plane in a supercluster.

A search for galaxy clusters in the Münster Red Sky Survey

The Voronoi tessellation technique is useful for finding galaxy structures in a two-dimensional galaxy distribution. The technique was used on a fragment of the Munster Red Sky Survey and yielded 7280 such structures in an area consisting of 2760 square degrees. The spatial positions of structures containing at least 30 members were compared with those of galaxy clusters from the Abell–Corwin–Olowin catalogue and resulted in a good correlation for rich objects. Large structures with numerous members frequently consist of smaller substructures.

The Adopted Morphological Types of 247 Rich PF Galaxy Clusters

Morphological types were determined for 247 rich galaxy clusters from the PF Catalogue of Galaxy Clusters and Groups. The adapted types are based on classical morphological schemes and consider concentration to the cluster center, the signs of preferential direction or plane in the cluster, and the positions of the brightest galaxies. It is shown that both concentration and preferential plane are significant and independent morphological criteria.

The Binggeli effect

We found the alignement of elongated clusters of BM type I and III (the excess of small values of the \Delta\theta angles is observed), having range till about 60Mpc/h. The first one is probably connected with the origin of supergiant galaxy, while the second one with environmental effects in clusters, originated on the long filament or plane.

Luminosity function for galaxy clusters

We constructed and studied the luminosity function of 6188 galaxy clusters. This was performed by counting brightness of galaxies belonging to clusters in the PF catalogue, taking galaxy data from MRSS. Our result shows that the investigated structures are characterized by a luminosity function different from that of optical galaxies and radiogalaxies (Machalski & God lowski 2000). The implications of this result for theories of galaxy formation are briefly discussed.

Construction of luminosity function for galaxy clusters

The luminosity function is an important quantity for analysis of large scale structure statistics, interpretation of galaxy counts (Lin & Kirshner 1996 ). We investigate the luminosity function of galaxy clusters. This is performed by counting the brightness of galaxies belonging to clusters in PF Catalogue. The obtained luminosity function is significantly different than that obtained both for optical and radiogalaxies (Machalski & Godowski 2000 ). The implications of this result for theories of galaxy formation are discussed as well.