Binil Aryal

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

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.

Coexistence of chiral symmetry restoration and random orientation of galaxies

We studied the chiral symmetry restoration and the spatial orientation of 2288 spiral and spiral barred galaxies that have radial velocities (RV) less than 5000 km s −1 . A random direction of the rotation of galaxies is assumed in order to classify the structural modes. The distribution of spin vector and spin vector projections of leading and trailing arm galaxies in the total sample and subsamples are studied. We use chi-square, auto-correlation and Fourier tests in order to discriminate the preferred alignments from the random alignments. A good correlation between the random alignment and the chiral symmetry is noticed in the Local Supercluster (RV < 3000 km s −1 ) and in galaxies nearby the Local Supercluster (3000 < RV (km s −1 ) ≤ 5000). Spiral galaxies show a similar result. The barred spirals show an opposite trend to that observed for the spirals. Nearby the Local Supercluster, we noticed a preferred spatial alignment and non-chiral property in the leading and trailing arm spiral barred galaxies. Our result predicts that the progressive loss of chirality might have some connection with the rotationally supported (spirals, barred spirals) and randomized (lenticulars, ellipticals) systems. Thus, we suspect that the dynamical processes in the cluster evolution give rise to a dynamical loss of chirality.

Asymmetric Mass-Loss on the AGB: Examples from IRAS Data

A wide-angle search for extended structures (arcs, filaments, cavities etc.) around ca. 400 Galactic planetary nebulae on IRAS SkyView maps revealed several candidates. Some of these dust structures can hardly be explained by chance superpositions of otherwise unrelated objects. They show clear signs of bi- or quadru-polar shape and will, due to their huge dimensions, probably have started to form already in the AGB phase. If so, then the mass-loss in the AGB phase is not spherically symmetric in a number of cases

Winding sense of galaxies around the local supercluster

We present an analysis of the winding sense (S and Z-shapes) of 1 621 field galaxies that have radial velocity between 3 000 km s -1 and 5 000 km s -1 . The preferred alignments of S- and Z-shaped galaxies are studied using chi-square, auto correlation and Fourier series tests. We classify all the galaxies into 32 subsamples and notice a good agreement between the position angle (PA) distribution of the S- and Z- shaped galaxies. The homogeneous distribution of the S- and Z-shaped galaxies is more noticeable for the late-type spirals (Sc, Scd, Sd and Sm) than for the early-types (Sa, Sab, Sb and Sbc). A significant dominance of S-mode galaxies is apparent in the barred spirals. A random alignment is evident in the PA-distribution of Z- and S-mode spirals. In addition, a homogeneous distribution of the S- and Z-shaped galaxies is found to be invariant under global expansion. The PA-distribution of the total S-mode galaxies is found to be random, whereas a preferred alignment is clear for all the Z-mode galaxies. It is found that the galactic planes of Z-mode galaxies tend to lie in the equatorial plane.

Preferred alignments of angular momentum vectors of galaxies in six dynamically unstable Abell clusters

A spatial orientation of angular momentum vectors of galaxies in six dynamically unstable Abell clusters (S1171, S0001, A1035, A1373, A1474 and A4053) is studied. For this, two-dimensional observed parameters (e.g., positions, diameters and position angles) are converted into three-dimensional (3D) rotation axes of the galaxy using the ‘position angle - inclination’ method. The expected isotropic distribution curves for angular momentum vectors are obtained by performing random simulations. The observed and expected distributions are compared using several statistical tests. No preferred alignments of angular momentum vectors of galaxies are noticed in all six dynamically unstable clusters, supporting the hierarchy model of galaxy formation. These clusters have a larger value of velocity dispersion. However, local effects are noticed in the clusters that have substructures in the 1D-3D number density maps.