| Evolution of global morphology of galaxy clusters as seen in the X-rays was measured, using a variety of morphological measures at different radii, and by accounting for Poisson noise in images. Ellipticities and the multipole-moment power ratios of Buote & Tsai (1995,1996), were used. The power ratios PR2, PR3, PR 4, and PRpk 1 served to quantify morphology. A sample of 143 galaxy clusters at redshifts 0.1028 < z < 1.273 was assembled using Chandra archive data as of August, 2006. Multiple observations of sources were merged, when available, for enhanced signal-to-noise. Galaxy cluster morphologies were probed in circular apertures whose radii were 300h-170 kpc and 500h-170 kpc. We find significant evolution of cluster morphology with redshift, as measured by PR3, PR4 , and PRpk 1 at the 3-4sigma level at both scales, with PR 3 exhibiting a sensitivity to noise-correction at 300h-170 kpc. Results for ellipticity and PR2 are consistent with no evolution. We find that PRpk 1 is an ideal staitistic to use for probing morphology evolution as it sees evolution at both scales, regardless of whether noise-correction is applied. Our results for evolution of PR2, PR3, and PR4 are fully consistent with previous observational work. Jeltema et al. (2005) see no consistency of PR4 at 500h-170 kpc with evolution when they apply their noise-correction, which is in disagreement with our results. Furthermore, our results for the evolution of cluster ellipticity with redshift fail to explain away, e.g., the predictions of Ho et al. (2006). |
