On the radial density profile of intracluster gas tracing the isothermal   dark halo with a finite core
  The cusped NFW universal density profile suggested by typical CDM models has been challenged in recent years by the discoveries of the soft cores for a broad range of masses from dwarf galaxies to clusters of galaxies. It is thus desirable that a new, analytic model would instead become available for virialized dark halos. One promising candidate is probably the empirical density profile proposed by Burkert, which resembles an isothermal profile with a constant core in the inner region and matches the NFW profile at large radii. Meanwhile, such a revised dark halo (RDH) profile has turned out a great success on galactic scales. This stimulates us to apply the RDH profile to more massive systems like clusters of galaxies. In this paper we have made an attempt to derive the radial density profile of intracluster gas from the RDH profile, and compare it with those revealed by X-ray observations and inferred from the NFW profile. It is shown that the RDH predicted gas density can be well represented by the conventional beta model with a typical beta parameter of 0.7-0.9. Fitting the theoretically predicted X-ray surface brightness profile to an ensemble of 45 X-ray clusters, we find that the RDH and NFW profiles become to be almost indistinguishable. Yet, the RDH profile allows us to work out straightforwardly the central dark matter density of clusters from X-ray measurements. Using the 45 clusters, we find that the central densities of clusters have an average value of ~0.01 solar mass pc^{-3}, in agreement with the result estimated on galactic scales, which reinforces the claim for the presence of the soft halo cores over the entire mass range. 
Xiang-Ping Wu and Yan-Jie Xue