Investigation of galactic alignment in Local Supercluster galaxy clusters

Abstract

A B S T R A C TWe investigate the orientations of the galactic axes within 18 selected clusters, substructures of the Local Supercluster. For every cluster we map the parameter D 11 describing the alignment of the galactic axes with respect to a chosen cluster pole, divided by its formal error jðD 11 Þ [s ϵ D 11 =jðD 11 Þ]. The cluster pole coordinates change along the entire celestial sphere. The resulting maps are analysed for correlations of their maxima with directions from the cluster centre to (i) the derived 'physical' cluster poles, (ii) the Local Supercluster centre, (iii) the Virgo A centre and (iv) the Earth, i.e. along the line of sight (ϵ LOS). The strong maximawith one exception -exist only for non-spiral (NS) subsamples, with the maximum well correlated with the LOS direction. Another of the studied directions may occur close to the maximum only if these directions are close to the LOS and they do not correlate with other features visible on the maps. For clusters with a clearly defined maximum of s below 3:0 the conclusion generally does not change. For the spiral (S) subsamples the maps are usually at the random noise level. In these cases a weaker, but still existing correlation with the LOS is observed and no other evident correlations are noted. We conclude that a strong systematic effect, generated by the process of deprojection of a galactic axis from its optical image, is present in the catalogue data. It can mask any weak alignment existing in the analysed clusters. With the use of a simple model for the systematic effect we are able to reproduce the main characteristic features of the maps for non-spiral galaxies. We note, however, that a few clusters show significant differences with respect to this model.

Substructures and galaxy orientations in clusters II. Cluster Abell 14

“…There is a correlation between the maximum of this ratio and the direction of the line of sight to the cluster. This result confirms our previous assumption that the effect described above (Godłowski & Ostrowski 1999) is present in our sample. According to us, the highly compact structure of the observed maximum is of special importance.…”

Galaxy Orientations in the Coma Cluster

“…Conversely, it is expected that groups and clusters show preferential alignments in the direction of the last major accretion episode (Faltenbacher et al 2005). Searches for alignments among the fainter cluster galaxies have generally returned ambiguous results, with some positive detections (Djorgovski 1983;Plionis et al 2003; as well as null results (Dekel 1985;Godlowski & Ostrowski 1999;Strazzullo et al 2005;). However, it is possible that the presence of anisotropy in galaxy position angles can only be detected in less evolved clusters (Plionis et al 2003), while it is also conceivable that only near neighbor galaxies are aligned with each other because they exert reciprocal tidal torques (Kitzbichler & Saurer 2003), or that radial alignments are induced by the cluster tidal field (Pereira & Kuhn 2005).…”

Spin vector orientations of galaxies in eight Abell clusters of BM type I

“…There are two camps in the field of galaxy orientation studies: one of these is searching for nonrandomness of the orientations of galaxies in the Local Supercluster (hereafter LSC) plane (e.g., Reinhardt & Roberts 1972;Jaaniste & Saar 1978, hereafter JS;MacGillivray et al 1982;Kapranidis & Sullivan 1983;MacGillivray & Dodd 1985a,b;Flin & Godlowski 1986, hereafter FG;Kashikawa & Okamura 1992, hereafter KO;Godlowski 1993, hereafter Go93;Godlowski 1994;Yuan et al 1997;Hu et al 1998). The other research direction is the investigation of the orientations of galaxies in other clusters (e.g., Hawley & Peebles 1975;Thompson 1976;MacGillivray et al 1982;Helou & Salpeter 1982;Djorgovski 1983Djorgovski , 1987Hoffman et al 1989;Trevese et al 1992;Hu et al 1995;Wu et al 1997;Godlowski et al 1998Godlowski et al , 1999Baier et al 2003), particularly in the well studied Virgo cluster (e.g., Hawley & Peebles 1975;Thompson 1976;MacGillivray et al 1982;Helou & Salpeter 1982;Djorgovski 1987;Hoffman et al 1989;Hu et al 1995) and Coma cluster (e.g., Hawley & Peebles 1975;Thompson 1976;Djorgovski 1987;Wu et al 1997;Flin 2001).…”