Chandra Observations of the Planck Early Sunyaev–Zeldovich Sample: A Reexamination of Masses and Mass Proxies

Using Chandra observations, we derive the Y-X proxy and associated total mass measurement, M-500(YX), for 147 clusters with z < 0.35 from the Planck early Sunyaev-Zeldovich catalog, and for 80 clusters with z < 0.22 from an X-ray flux-limited sample. We reextract the Planck YSZ measurements and obtain the corresponding mass proxy, M-500(SZ), from the full Planck mission maps, minimizing Malmquist bias due to observational scatter. The masses reextracted using the more precise X-ray position and characteristic size agree with the published PSZ2 values, but yield a significant reduction in the scatter (by a factor of two) in the M-500(SZ) - M-500(YX) relation. The slope is 0.93 +/- 0.03, and the median ratio, M-500(SZ)/M-500(YX) = 0.91 +/- 0.01, is within the expectations from known X-ray calibration systematics. Y-SZ/Y-X is 0.88 +/- 0.02, in good agreement with predictions from cluster structure, and implying a low level of clumpiness. In agreement with the findings of the Planck Collaboration, the slope of the Y-SZ-D-A(-2) Y-X flux relation is significantly less than unity (0.89 +/- 0.01). Using extensive simulations, we show that this result is not due to selection effects, intrinsic scatter, or covariance between quantities. We demonstrate analytically that changing the Y-SZ-Y-X relation from apparent flux to intrinsic properties results in a best-fit slope that is closer to unity and increases the dispersion about the relation. The redistribution resulting from this transformation implies that the best-fit parameters of the M-500(SZ) - M-500(YX) relation will be sample- dependent.