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, ${M}_{500}^{{Y}_{{\rm{X}}}}$ , 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 Y_SZ measurements and obtain the corresponding mass proxy, ${M}_{500}^{\mathrm{SZ}}$ , 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 ${M}_{500}^{\mathrm{SZ}}$ - ${M}_{500}^{{Y}_{{\rm{X}}}}$ relation. The slope is 0.93 ± 0.03, and the median ratio, ${M}_{500}^{\mathrm{SZ}}/{M}_{500}^{{Y}_{{\rm{X}}}}=0.91\pm 0.01$ , 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- ${D}_{{\rm{A}}}^{-2}{Y}_{{\rm{X}}}$ 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 ${M}_{500}^{\mathrm{SZ}}$ - ${M}_{500}^{{Y}_{{\rm{X}}}}$ relation will be sample-dependent.