Lensing as a test for no CDM models

Zhao et al. (astro-ph/0509590) tested lensing in Beckenstein's
relativistic MOND (TeVeS), and conclude that lensing may be a good test
for CDM theories. They found that "TeVeS succeeds in providing an
alternative to general relativity in some lensing contexts; however, it
faces significant challenges when confronted with particular galaxy lens
systems". However they could not eliminate it for all choices of
parameters.

The teleconnection model predicts geodesic motion for a classical ray of
light so that there is no change in the prediction of bending of light
around a body of known mass, such as the sun. Lensing is affected in two
ways: in the absence of a CDM halo, lower galactic masses will lessen
lensing but this is offset by the increase in distance to a lens at
high redshift. Each observed lens requires careful analysis, but at the
accuracy of current observation it appears unlikely that lens masses
will provide a definitive test.

A clearer test may be the analysis of the profile of the halo. Martel
and Shapiro have examined the profile of a number of lenses and find
that they do not correctly reproduce the central region; "CDM N-body
halos show density profiles which vary as ro~r^-alpha, alpha~1, instead
of a small flat core". 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. These
results are not consistent with the standard CDM model of galactic
haloes, but they are, of course, trivially the case in a no CDM model.


Regards

--
Charles Francis
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