The Absence of Adiabatic Contraction of the Radial Dark Matter Profile in the Galaxy Cluster A2589

We present an X-ray analysis of the radial mass profile of the radio-quietgalaxy cluster A2589 between 0.015-0.25 r_vir using an XMM-Newton observation.Except for a ~16 kpc shift of the X-ray center of the R=45-60 kpc annulus,A2589 possesses a remarkably symmetrical X-ray image and is therefore anexceptional candidate for precision studies of its mass profile by applyinghydrostatic equilibrium. The total gravitating matter profile is well describedby the NFW model (fractional residuals <~10%) with c_vir=6.1 +/- 0.3 and M_vir= 3.3 +/- 0.3 x 10^{14} M_sun (r_vir = 1.74 +/- 0.05 Mpc) in excellentagreement with LCDM. When the mass of the hot ICM is subtracted from thegravitating matter profile, the NFW model fitted to the resulting dark matter(DM) profile produces essentially the same result. However, if a componentaccounting for the stellar mass (M_*) of the cD galaxy is included, then theNFW fit to the DM profile is substantially degraded in the central r ~50 kpcfor reasonable M_*/L_V. Modifying the NFW DM halo by adiabatic contractionarising from the early condensation of stellar baryons in the cD galaxy furtherdegrades the fit. The fit is improved substantially with a Sersic-like modelrecently suggested by high resolution N-body simulations but with an inverseSersic index, alpha ~0.5, a factor of ~3 higher than predicted. We argue thatneither random turbulent motions nor magnetic fields can provide sufficientnon-thermal pressure support to reconcile the XMM mass profile with adiabaticcontraction of a CDM halo assuming reasonable M_*/L_V. Our results support thescenario where, at least for galaxy clusters, processes during halo formationcounteract adiabatic contraction so that the total gravitating mass in the coreapproximately follows the NFW profile.Comment: 15 pages, 11 figures, accepted for publication in ApJ. Minor changes to match published versio