X-ray surface brightness fluctuations in the core ( 650 \times 650 kpc ) region of the Coma cluster observed with XMM-Newton and Chandra are analyzed using a 2D power spectrum approach .
The resulting 2D spectra are converted to 3D power spectra of gas density fluctuations .
Our independent analyses of the XMM-Newton and Chandra observations are in excellent agreement and provide the most sensitive measurements of surface brightness and density fluctuations for a hot cluster .
We find that the characteristic amplitude of the volume filling density fluctuations relative to the smooth underlying density distribution varies from 7-10 % on scales of \sim 500 kpc down to \sim 5 % at scales \sim 30 kpc .
On smaller spatial scales , projection effects smear the density fluctuations by a large factor , precluding strong limits on the fluctuations in 3D .
On the largest scales probed ( hundreds of kpc ) , the dominant contributions to the observed fluctuations most likely arise from perturbations of the gravitational potential by the two most massive galaxies in Coma , NGC4874 and NGC4889 , and the low entropy gas brought to the cluster by an infalling group .
Other plausible sources of X-ray surface brightness fluctuations are discussed , including turbulence , metal abundance variations , and unresolved sources .
Despite a variety of possible origins for density fluctuations , the gas in the Coma cluster core is remarkably homogeneous on scales from \sim 500 to \sim 30 kpc .