364 research outputs found
Photometric and kinematical study of nearby groups of galaxies around IC 65 and NGC 6962
We discuss the structure, galaxy content and kinematics of a sparse, probably
collapsing group around IC 65 and an evolved rich group around NGC 6962Comment: Poster contribution on 2 pages with 2 figures to be published in ESO
Astrophysics Symposia: "Groups of Galaxies in the Nearby Universe", eds. I.
Saviane, V. Ivanov, J. Borissov
Dynamics and Shape of Brightest Cluster Galaxies
We identified Brightest Cluster Members (BCM) on DSS images of 1083 Abell
clusters, derived their individual and host cluster redshifts from literature
and determined the BCM ellipticity. Half the BCMs move at a speed higher than
37 % of the cluster velocity dispersion sigma_{cl}, suggesting that most BCMs
are part of substructures falling into the main cluster. Both, the BCM's
velocity offset in units of sigma_{cl}, and BCM ellipticity, weakly decrease
with cluster richness.Comment: 2 pages, 2 figures, Proc. ESO Workshop "Groups of galaxies in the
nearby Universe", Santiago, Chile, 5-9 Dec. 2005, ESO Astrophysics Symposia,
eds. I. Saviane, V. Ivanov & J. Borissova, Springer-Verla
Alignment of galaxies relative to their local environment in SDSS-DR8
We study the alignment of galaxies relative to their local environment in
SDSS-DR8 and, using these data, we discuss evolution scenarios for different
types of galaxies. We defined a vector field of the direction of anisotropy of
the local environment of galaxies. We summed the unit direction vectors of all
close neighbours of a given galaxy in a particular way to estimate this field.
We found the alignment angles between the spin axes of disc galaxies, or the
minor axes of elliptical galaxies, and the direction of anisotropy. The
distributions of cosines of these angles are compared to the random
distributions to analyse the alignment of galaxies. Sab galaxies show
perpendicular alignment relative to the direction of anisotropy in a sparse
environment, for single galaxies and galaxies of low luminosity. Most of the
parallel alignment of Scd galaxies comes from dense regions, from 2...3 member
groups and from galaxies with low luminosity. The perpendicular alignment of S0
galaxies does not depend strongly on environmental density nor luminosity; it
is detected for single and 2...3 member group galaxies, and for main galaxies
of 4...10 member groups. The perpendicular alignment of elliptical galaxies is
clearly detected for single galaxies and for members of < 11 member groups; the
alignment increases with environmental density and luminosity. We confirm the
existence of fossil tidally induced alignment of Sab galaxies at low z. The
alignment of Scd galaxies can be explained via the infall of matter to
filaments. S0 galaxies may have encountered relatively massive mergers along
the direction of anisotropy. Major mergers along this direction can explain the
alignment of elliptical galaxies. Less massive, but repeated mergers are
possibly responsible for the formation of elliptical galaxies in sparser areas
and for less luminous elliptical galaxies.Comment: 15 pages, 15 figures, accepted for publication in A&
Wavelet analysis of the formation of the cosmic web
According to the modern cosmological paradigm galaxies and galaxy systems
form from tiny density perturbations generated during the very early phase of
the evolution of the Universe. Using numerical simulations we study the
evolution of phases of density perturbations of different scales to understand
the formation and evolution of the cosmic web. We apply the wavelet analysis to
follow the evolution of high-density regions (clusters and superclusters) of
the cosmic web. We show that the positions of maxima and minima of density
waves (their spatial phases) almost do not change during the evolution of the
structure. Positions of extrema of density perturbations are the more stable,
the larger is the wavelength of perturbations. Combining observational and
simulation data we conclude that the skeleton of the cosmic web was present
already in an early stage of structure evolution.Comment: 12 pages, 8 figures, revised versio
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