Offset between dark matter and ordinary matter: evidence from a sample
  of 38 lensing clusters of galaxies
  We compile a sample of 38 galaxy clusters which have both X-ray and strong
lensing observations, and study for each cluster the projected offset between
the dominant component of baryonic matter center (measured by X-rays) and the
gravitational center (measured by strong lensing). Among the total sample, 45%
clusters have offsets >10". The >10" separations are significant, considering
the arcsecond precision in the measurement of the lensing/X-ray centers. This
suggests that it might be a common phenomenon in unrelaxed galaxy clusters that
gravitational field is separated spatially from the dominant component of
baryonic matter. It also has consequences for lensing models of unrelaxed
clusters since the gas mass distribution may differ from the dark matter
distribution and give perturbations to the modeling. Such offsets can be used
as a statistical tool for comparison with the results of Lambda-CDM simulations
and to test the modified dynamics.
