Orientation Of Galaxies In Clusters Research Articles

A New Method of Investigation of the Orientation of Galaxies in Clusters in the Absence of Information on Their Morphological Types

The analysis of the orientation of galaxies is one of the most widely used tools in the fields of extragalactic astronomy and cosmology, enabling the verification of structure formation scenarios in the universe. It is based on the statistical analysis of the distribution of angles, giving the spatial orientation of galaxies in space. In order to obtain the correct analysis results, one is obliged to take into account the Holmberg effect and the fact that galaxies are oblate spheroids, with the real axis ratio depending on the morphological type. However, most of the astronomical data available today do not contain information about the morphological types of galaxies. The analysis of sufficiently numerous observational data allows one to calculate the estimated frequency of the occurrence of given morphological types used in the proposed method. As a part of this, on the basis of these frequencies, simulations were performed, which enabled us to recognize new angle distributions used in orientation studies. These distributions already contain information on the frequency of the appearance of galaxies of particular morphological types in clusters, allowing for more accurate results of the statistical tests carried out during the analysis. The method is an extension of results developed in in our previous investigations.

Investigation of the orientation of galaxies in clusters: the importance, methods and results of research

Various models of structure formation can account for various aspects of the galaxy formation process on different scales, as well as for various observational features of structures. Thus, the investigation of galaxies orientation constitute a standard test of galaxies formation scenarios since observed variations in angular momentum represent fundamental constraints for any model of galaxy formation. We have improved the method of analysis of the alignment of galaxies in clusters. Now, the method allows to analyze both position angles of galaxy major axes and two angles describing the spatial orientation of galaxies. The distributions of analyzed angles were tested for isotropy by applying different statistical tests. For sample of analyzed clusters we have computed the mean values of analyzed statistics, checking whether they are the same as expected ones in the case of random distribution of analyzed angles. The detailed discussion of this method has been performed. We have shown how to proceed in many particular cases in order to improve the statistical reasoning when analyzing the distribution of the angles in the observational data. Separately, we have compared these new results with those obtained from numerical simulations. We show how powerful is our method on the example of galaxy orientation analysis in 247 Abell rich galaxy clusters. We have found that the orientations of galaxies in analyzed clusters are not random. It means that we genuinely confirmed an existence of the alignment of galaxies in rich Abells' galaxy clusters. This result is independent from the clusters of Bautz-Morgan types.

Some aspects of the orientation of galaxies in clusters

The analysis of Tully’s groups of galaxies belonging to the Local Supercluster (LSC) was performed. In the 1975 Hawley and Peebles [D. I. Hawley, P. J. E. Peebles, Astron. J. 80, 477 (1975)] presented the method for investigations of the galaxies orientation in the large structures. In our previous papers [W. God lowski, P. Piwowarska, E. Panko, P. Flin, Astron. J. 723, 985 (2010); W. God lowski, Astrophys. J. 747, 7 (2012)] the statistical test proposed by Hawley and Peebles for the investigation of this problem was analyzed in detail and some improvements were suggested. On this basis the new method of the analysis of galactic alignment in clusters was proposed. Using this method, God lowski [W. God lowski, Acta Phys. Polon. B 42, 2323 (2011)] analyzed the orientation of galaxies inside Tully’s groups founding no significant deviations from isotropy both in orientation of position angles and D and angles as well, giving the spatial orientation of galaxy planes. In the present paper we examined carefully and methodically the dependence of alignment in Tully’s groups on the morphological type of galaxies. Moreover, we discussed the consequences of dierent approximation of “true shape” of the galaxies for dierent morphological types, a possible influence of this problem for the investigation of spatial orientation of galaxies. In addition, we discussed the implications of the obtained results for the theory of galaxy formation as well.

The orientation of galaxies in clusters

We present a statistical analysis of directional data for the 10-20 brightest galaxies in a sample of 55 clusters. The data are derived from the digitization of Palomar 48 in. Schmidt telescope plates. We consider the orientation of clusters, of each galaxy, the direction of the line joining each galaxy with the cluster center or with the brightest galaxy, and all possible relative angles between these directions. We apply various statistical tests and we find no significant alignment for galaxies fainter than the two first ranked cluster members. We confirm a strong alignment of the brightest galaxy major axis with the long axis of the parent cluster

Monte-carlo simulation of the orientations of galaxies in clusters

A Monte-Carlo technique has been used in order to simulate the orientations of galaxies in spherically symmetric clusters. Analysis of the distributions for projected orientations and shapes of the member galaxies indicates that non-random effects are not the result of projection of an otherwise random distribution, but must have a basis in physical reality. The distribution of orientations for galaxies in the field of the cluster 0047–2946 can be understood as a distribution in which 50% of the galaxies belong to the field and are aligned at random with respect to the cluster centre, while the majority of the cluster galaxies are aligned with their major planes pointing in the direction of the cluster centre.

Orientation of spiral galaxies as a test of theories of galaxy formation

The cosmological turbulence theory and the theory of adiabatic fluctuations predict different orientations of galaxies in clusters and superclusters. the first theory favours the alignment of the planes of galaxies with the supergalactic plane, whereas the planes of spiral galaxies formed according to the second theory are perpendicular to the plane of a supergalaxy.