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We use high-resolution hydrodynamic simulations to investigate the densityprofile of hot gas in clusters of galaxies, adopting a variant of cold darkmatter cosmologies and employing a cosmological N-body/smoothed particlehydrodynamics code to follow the evolution of dark matter and gas. In additionto gravitational interactions, gas pressure, and shock heating, we includebremsstrahlung cooling in the computation. Dynamical time, two-body relaxationtime, and cooling time in the simulations are examined to demonstrate that theresults are free from artificial relaxation effects and that the time step isshort enough to accurately follow the evolution of the system. In thesimulation with nominal resolution of 66h^{-1} kpc the computed cluster appearsnormal, but in a higher (by a factor 2) resolution run, cooling is so efficientthat the final gas density profile shows a steep rise toward the cluster centerthat is not observed in real clusters. Also, the X-ray luminosity of7\times10^{45} ergs s^{-1} far exceeds that for any cluster of the computedtemperature. The most reasonable explanation for this discrepancy is that thereare some physical processes still missing in the simulations that actuallymitigate the cooling effect and play a crucial role in the thermal anddynamical evolution of the gas near the center. Among the promising candidateprocesses are heat conduction and heat input from supernovae. We discuss theextent to which these processes can alter the evolution of gas.Comment: 19 pages, 5 postscript figures included; uses aaspp4.sty (AASTeX  v4.0); title changed; final version published in The Astrophysical Journa

The Effect of Cooling on the Density Profile of Hot Gas in Clusters of Galaxies: Is Additional Physics Needed?