Environmental Engineering Reference
In-Depth Information
1 Introduction
Galaxies are the basic building blocks of the large scale structure of the universe.
They were classified according to their morphology by Hubble. There are elliptical,
spiral, and irregular galaxies. Spiral galaxies are the main object in this work; they
are composed of a bulge, a spherical distribution of stars at the center of the galaxy;
a disc of stars, gas and dust; and a halo of dark matter, of unknown particles, that
only acts gravitationally on the other components. Recently Sellwood has published
a review (Sellwood
2014
) that discusses several aspects of current interest in the
research of disc galaxies.
In the present work, we study bars in interacting spiral galaxies. Observations of
spiral galaxies indicate that the presence of a bar is a common feature (Elmegreen and
Elmegreen
1983
;Masteretal.
2011
). In particular Master et al. (
2011
) have found
that 29.4% of the galaxies in the sample they analyse have a bar. The bar formation
in isolated models has been widely studied both analytically and numerically (Hohl
1971
; Sellwood
1981
; Sellwood and Carlberg
1984
; Athanassoula and Sellwood
1986
; Weinberg
1985
; Debattista and Sellwood
2000
; Weinberg and Katz
2002
). In
this paper we consider the dynamical effects of non-isolated systems which are found
in clusters of galaxies. In this sense, it has been suggested that the observed bar in
many spirals is the result of the gravitational interaction between two or more nearby
galaxies. For instance, Nogushi (
1987
) has found that during the collision of two
galaxies and between the first and the second closest approaches, the disc develops
a transient bar shape. The gravitational interaction between the two galaxies gives
rise to perturbations in the orbits of the stars that results in the formation of the bar.
Bar formation in stellar discs depends upon various simultaneous effects. In the
case of collisions, simulations have shown that these factors are (Salo
1990
): rotation
curve shape, disc-halo mass ratio, perturbation force and geometry. Additionally,
simulations suffer fromnumerical effects such as low spatial and temporal resolution,
too few particles representing the system, and an approximate force model. These
effects were studied by Gabbasov (
2006
) and Gabbasov et al. (
2006
) where it was
shown that specific parameter choices may change bar properties. Once numerical
effects are controlled, we may investigate all the other model parameters, which in
our case are: geometric parameters such as impact parameter and the angle between
the disc planes.
In thisworkwe study themorphology of bars that forms as a product of instabilities
that result of the collision of two spiral galaxies. Morphology is given by finding
major and minor axes evolution after the first encounter of the spirals.
Our work is organised in the following form: In the next section we present how
to build a galaxy model by following the Hernquist method (Hernquist
1990
) and
explain how to set up the parabolic collision geometry. Next, we discuss our results
for various collision cases such as off-axis impacts and for two different angles of
collision of the disc galaxies and show the resultant morphological properties of
tidally formed bars. Conclusions are shown in the final section.
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