R. Salinas, T. Richtler, L. P. Bassino, A. J. Romanowsky, Y. Schuberth
The dark matter halos of field elliptical galaxies are not well studied and
appear controversial in the literature. There are galaxies seeming nearly
devoid of dark matter and others showing clear signatures of its presence.
Furthermore, the MOND prescription, which has been shown predictive power in
the domain of disk galaxies, has not been investigated for isolated elliptical
galaxies. We study the kinematics of the isolated elliptical NGC 7507 which has
been claimed as a clear case of dark matter presence in early-type galaxies. We
obtained major and minor axis long slit spectroscopy of NGC 7507 using the
Gemini South telescope and deep imaging in Kron-Cousins R and Washington C
using the CTIO/MOSAIC camera. Mean velocities, velocity dispersion and higher
order moments are measured out to \sim90". The galaxy presents significant
rotation along the minor axis and a rapidly declining velocity dispersion in
both axes. The velocity dispersion profile is modeled in the context of
spherical Jeans analysis. Models without DM provide an excellent representation
of the data with an M/L ratio of 3.1 (R-band). The most massive NFW halo the
data allows has a virial mass of only 3.9+3.1-2.1E11 solar masses, although the
data favor models with slight radial anisotropy which implies an even lower DM
halo mass of 2.2+2.0-1.2E11 solar masses. Modeling of the h4 Gauss-Hermite
coefficient is inconclusive but seems to favor the presence of some radial
anisotropy. A cored logarithmic DM halo with parameters r0 = 7 kpc and v0 = 100
km/s can also reproduce the observed velocity dispersion profile. MOND
predictions overestimate the velocity dispersion. In conclusion, we cannot
easily reproduce the previously found dominance of dark matter in NGC 7507
within a simple spherical model. Dark matter may be present, but only in
conjunction with a strong radial anisotropy, for which there are some
indications.
View original:
http://arxiv.org/abs/1111.1581
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