Spatial orientation of galaxies in the core of the Shapley concentration – the cluster Abell 3558

Abstract

We present an analysis of the spatial orientations of 323 galaxies in the cluster Abell 3558. Our aim is to examine non-random effects in galaxy orientations in the subsample of the cluster. The "position angle-inclination" method is used to find the threedimensional rotation axes. To check for anisotropy or isotropy we carried out three statistical tests: Fourier, Kolmogorov-Smirnov, and Kuiper-V. We assumed a spatially isotropic distribution to examine non-random effects. The galaxies found in the investigated cluster region show isotropy in both two-and three-dimensional analyses of the galactic coordinate system. In addition, it is found that the overall isotropic appearance cannot be maintained when looking at the subsamples. The low radial-velocity galaxies in A 3558 showed anisotropy in both two-and three-dimensional analyses. A weak anisotropy is noticed in the hard X-ray emission region. Few subsamples shows similar alignments with respect to both the galactic and Supergalactic coordinate systems. We offer possible explanations of these anisotropies.Article published by EDP Sciences and available at http://www.edpsciences.org/aa or http://dx.

The Galaxy Alignment Effect in Abell 1689: Evolution, Radial, and Luminosity Dependence

“…Direct galaxy alignments have been detected for some clusters (Plionis et al 2003; but not in others (Strazzullo et al 2005;Aryal, Kandel & Saurer 2006). It is likely that the alignments depend on mass, cluster age and position in complex ways.…”

Spatial orientations of galaxies in seven Abell clusters of BM type II

“…According to the ‘hierarchy model’ (Peebles 1969) the directions of the rotation axes should be distributed randomly. Authors have drawn different conclusions regarding these scenarios: (1) no preferred alignment (Helou & Salpeter 1982; Bukhari & Cram 2003; Aryal & Saurer 2005c), (2) tend to orient parallel (Jaaniste & Saar 1978; Flin & Godlowski 1986; Godlowski 1993, 1994; Godlowski, Baier & MacGillivray 1998; Flin 2001) or perpendicular (Reinhardt & Roberts 1972; Gregory, Thompson & Tifft 1981; MacGillivray et al 1982; Baier, Godlowski & MacGillivray 2003) with respect to the cluster [or local supercluster (LSC)] plane, (3) bimodal tendency (Kashikawa & Okamura 1992), (4) local anisotropy (Djorgovski 1983; Flin 1995; Aryal & Saurer 2004, 2005a, 2006; Aryal, Kandel & Saurer 2006), (5) global anisotropy (Parnovsky, Karachentsev & Karachentseva 1994), etc. Godlowski & Ostrowski (1999) noticed a strong systematic effect, generated by the process of deprojection of a galactic axis from its optical image.…”

The Alignment of Galaxies in Structures – Review

“…Independently, the same method was used to investigate the relationship between the arrangement of the orientation of galaxies and their morphological type according to the Bautz-Morgan classification (BM) and the dispersion of the velocity of galaxies in clusters. In particular, in the work of [98] it was found, contrary to the suggestion of Aryal and Saurer (2004, 2005b, 2005c, 2006, Aryal, Pudel and Saurer (2007) [123,228,233,236,237] that the alignment of the orientation of galaxies is weakly correlated with their morphological type according to the Bautz-Morgan classification (BM). The correlation suggested by Plionis et al (2003) [238] between the degree of alignment of galaxy orientation and the dispersion of galaxies in clusters has also not been confirmed.…”

“…This work showed that the main causes of their occurrence were contamination of the samples by background objects and difficulties in correct interpretation of the results obtained, due to the use of the equatorial coordinate system instead of the Supergalactic system. The importance of choosing the right coordinate system was also pointed out by Flin (1994) [120], Godłowski (1995) [121], Bukhari and Cram (2003) [122], Wu (2006) [107], and especially Aryal, Kandel and Saurer (2006) [123], who showed that the interpretation of the results of studies on the orientation of galaxies in the core of the Shapley Concentration -the cluster Abell 3558 -depends on the coordinate system used. It is also worth noting the results of the work of Kapranidis and Sullivian (1983) [119] who analyzed, in the equatorial coordinate system, the density of the position of the poles of galaxies in regions of size 30 0 x30 0 for a sample of spiral galaxies.…”

“…In a series of papers Aryal and his colaborators [123,228,233,236,237] dealt with the orientation of galaxies in 32 clusters of different sizes. They confirmed in [233] a picture in which we do not detect the orientation alignment of galaxies in small clusters, but such an alignment is observed in a number of rich galaxy clusters.…”