Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 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.

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The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph
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The categories of this paper are: eess
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The categories of this paper are: adap-org
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The categories of this paper are: stat
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
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The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci