Milky Way Rotation Curve

In article , Charles
Francis writes:
...in the instance of dark matter haloes we do
now have observations which show up inconsistencies. To explain the
rotation curves we observe the dark matter haloes must a particular
profile. This is not a profile which we can derive in any analytic model
of galaxy evolution, but more significantly it is not the profile which
we observe in lensing. Measurements of lensing give dark matter profiles
which follow the same (or at least similar) mass distribution as visible
matter.

While most of the problems with CDM may be written off as "we don't have
a theory yet", lensing profiles show a straight contradiction with
rotation curves.

Could you please provide references? What observations rule out
spherical dark matter haloes, and what lensing observations are
inconsistent with them?

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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Could you please provide references? What observations rule out
spherical dark matter haloes, and what lensing observations are
inconsistent with them?

There is actually a three way conflict between evolutionary models,
lensing and rotation curves. More references can be found in the refs.

According to evolutionary models dark matter halos should have steep
central density cusps (e.g., Navarro, Frenk, & White 1997) but they
appear not to (e.g., de Blok, Bosma, & McGaugh 2003; Swaters et al.
2003). In a survey of about 3000 galaxies, Biviano & Salucci (2006)
find that X-ray determination of the baryonic component of dark matter
haloes fits evolutionary models, but subhalo components do not. Martel
and Shapiro (2003) have examined the profile of lenses for a number of
evolutionary models. While they find quantitative fits for many
properties, they find that the models do not correctly reproduce the
central region. Park and Ferguson (2003) studied the lensing produced
by Burkert haloes and found, `For the scaling relation that provides
the best fits to spiral-galaxy rotation curve data, Burkert halos will
not produce strong lensing, even if this scaling relation extends up
to masses of galaxy clusters. Tests of a simple model of an
exponential stellar disk superimposed on a Burkert-profile halo
demonstrate that strong lensing is unlikely without an additional
concentration of mass in the galaxy center (e.g. a bulge)'.

Power et al (2003) also comment on discrepancies between analytic
models and halo distribution required by galaxy rotation curves. In
particular they state `there is no well defined value for the central
density of the dark matter, which can in principle climb to
arbitrarily large values near the centre'. Of this result they say
`there have been a number of reports in the literature arguing that
the shape of the rotation curves of many disk galaxies rules out
steeply divergent dark matter density profiles' and conclude that it
`may signal a genuine crisis for the CDM paradigm on small scales'.
On the other side of the debate, Milgrom and Sanders (2005) found
halo properties in Ursa Major Galaxies consistent with MOND
predictions, and in a one study for which a particularly good analysis
is possible, Wayth et al. (2005) found that, for the optical Einstein
ring gravitational lens ER 0047-2808, lensing is consistent with a
halo of the same mass distribution as the galaxy itself. This result
is not consistent with either the halo distribution required to
produce galactic rotation curves, or with evolutionary halo models. It
is, of course, trivially consistent with both in a no CDM model.

Biviano A. & Salucci P., The radial profiles of the different mass
components in galaxy clusters accepted in A&A. astro-ph/0511309.
de Blok, W.J.G., Bosma, A., & McGaugh, S.S. 2003, MNRAS, 340, 657.
Martel. H. and Shapiro P. R., 2003, Printed 4 March 2006, MNRAS, astro-ph/0305174
Navarro, J. F., Frenk, C. S., & White, S. D. M. 1997, ApJ, 490, 493.
Park Y., Ferguson H. C., 2003, Ap.J. 589, L65-L68, astro-ph/0304317
Power C., Navarro. J. F., Jenkins A., Frenk C. S., White S. D. M.,
Swaters, R.A., Madore, B.F., van den Bosch, F.C., & Balcells, M. 2003,
ApJ, 583, 732
Wayth R. B., Warren S. J., Lewis G. F., Hewett P. C., 2005, MNRAS, 360,
1333-1344.


Regards

--
Charles Francis
substitute charles for NotI to email