FUNA Lunch Talk:

Gerrit Schellenberger

Angelander-Institut fur Astronomie

X-ray Cross Calibration and Cosmology Using HIFLUGCS Galaxy Clusters

May 9

12:10PM, Room 230, NRAO, Edgemont Road


Cosmological constraints from clusters rely on accurate gravitational mass estimates, which strongly depend on cluster gas temperature measurements. Therefore, systematic calibration differences may result in biased, instrument-dependent cosmological constraints. This is of special interest in the light of the tension between the Planck results of the primary temperature anisotropies of the CMB and Sunyaev-Zel'dovich plus X-ray cluster counts analyses. I quantify in detail the systematics and uncertainties of the cross-calibration of the effective area between five X-ray instruments, EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the influence on temperature measurements. Furthermore, I assess the impact of the cross calibration uncertainties on cosmology. Using the HIFLUGCS sample, consisting of the 64 X-ray brightest galaxy clusters, I constrain the ICM temperatures through spectral fitting in the same, mostly isothermal, regions and compare them. Performing spectral fitting in the full energy band I find that best-fit temperatures determined with XMM-Newton/EPIC are significantly lower than Chandra/ACIS temperatures. I demonstrate that effects like multitemperature structure cannot explain the observed differences. I conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full energy band temperature profiles for cluster mass determination results in an 8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values in a cosmological analysis of a complete sample of galaxy clusters. For this conclusion, the Tinker+08 halo mass function was used, which is a sensitive probe of cosmological parameters. Such a shift is insufficient to significantly alleviate the tension between Planck CMB anisotropies and SZ plus XMM-Newton cosmological constraints. I will close by giving an outlook on what difficulties occur when deriving hydrostatic masses and constraining cosmological parameters from a complete sample.