Issue |
A&A
Volume 391, Number 2, August IV 2002
|
|
---|---|---|
Page(s) | 471 - 479 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20020832 | |
Published online | 02 August 2002 |
Large-scale asymmetry of rotation curves in lopsided spiral galaxies
Department of Physics, Indian Institute of Science, Bangalore 560 012, India
Corresponding author: cjjog@physics.iisc.ernet.in
Received:
11
January
2002
Accepted:
4
June
2002
Many spiral galaxies show a large-scale asymmetry with
a dependence in their
rotation curves as well as in their morphology, such as M 101 and NGC 628.
We show that both these features
can be explained by the response of a galactic disk to an imposed lopsided
halo potential.
A perturbation potential of
is deduced for the
morphologically lopsided galaxies in the Rix & Zaritsky ([CITE]) sample.
This is shown to result in a difference of
or ≥20–30 km s-1
in the rotation velocity on the two sides of the major axis.
Interestingly, the observed isophotal asymmetry in a typical
spiral galaxy is not much smaller and it results in a velocity
asymmetry of
or ~14–21
. Hence, we predict that most
spiral galaxies show a fairly significant rotational asymmetry.
The rotation velocity is shown to be maximum along the elongated
isophote –
in agreement with the observations along the SW in M 101,
while it is minimum along the opposite direction. This result leads to the
distinctive asymmetric shape of the
rotation curve which rises more steeply in one half of the
galaxy than the other, as observed by Swaters et al. ([CITE]). This shape is
shown to be a robust feature and would result for any centrally concentrated
disk. The net disk lopsidedness and hence the asymmetry in the rotation curve
is predicted to increase with radius and hence can be best studied
using HI gas as the tracer.
Key words: galaxies: kinematics and dynamics / galaxies: ISM / galaxies: spiral / galaxies: structure / galaxies: halos
© ESO, 2002
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