We use a complete sample of 38 richest maxBCG clusters to study the ICM-galaxy scaling relations based on X-ray and optical observations. The clusters are selected from the two largest bins of optical richness in the Planck stacking work with the maxBCG richness N200 > 78. We analyze their Chandra and XMM-Newton data to derive the X-ray properties of the ICM. While the expected cluster temperatures should be scattered around 5 - 10 keV from the optical richness, the observed range extends to temperatures as low as 1.5 keV. Meanwhile, they follow normal LX-TX and LX-YX relations, which suggests that they are normal X-ray clusters. Moreover, the observed average YX is consistent with the expected YX inferred from the Planck mean staking YSZ in the same two richest bins. However, the scatter of the LX-N and YX-N relations are also large and asymmetric with more outliers towards lower LX or YX. The mismatch between ICM-galaxy scaling relations can come from several factors, including miscentering, projection, contamination of low mass systems, mass bias and covariance bias. Our results suggest that results from blind stacking should be interpreted carefully. We also evaluate the fractions of relaxed and cool core (CC) clusters in our sample. Both are smaller than those from SZ or X-ray selected samples.

ABSTRACT

INTRODUCTION

abc

RESULTS DISCUSSIONQuestion: where does the mismatch come from?(1) ICM part: Fig. c shows consistency between X-ray and SZ observations.●The calibration and contamination of the SZ signal.●The assumed pressure profile and the X-ray scaling relation.Fig. e shows the clusters fllow normal LX-YX relation.●X-ray-dark-but-optical-normal clusters.

(2) Galaxy part: Fig. a shows low TX clusters are without Planck detection.●Contamination of low mass system.Fig. c shows miscentering and projection induce large scatter.●Miscentering: some flux moves outside of the aperture.●Projection: M~N, L~N2. 1N~1M~1L. 2N~2M~4L=2 project L+L.

Cyan circle: maxBCG r500 region Green circle: redMaPPer r500 region(3) Mass bias: Fig. a shows including the mass biase reduce the mismatch.

Assuming: hydrostatic mass= true cluster mass=weak-lensing mass.Results: mismatch emerges.●Thus the asumption is wrong, there are mass biases both from hydrostatic mass and weak-lensing mass.

Byproduct: as an optically selected sample, comparing the fraction of relaxed and cool core clusters with SZ and X-ray selected sample.

The mismatch of ICM-galaxy scaling ration comes from 1) miscentering, ~10%; 2) projection, ~10%; 3) contamination of low mass systems, ~10-15%; 4) hydrostatic mass bias, ~10-30%; 5) weak-lensing mass bias, ~10%; and 6) covariance bias, ~10%. These biases mix in some cases and can compensate with each other, but the dominant one is likely the mass bias.

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CONCLUSIONS

Puzzle: all the model SZ fluxes from optically selected clusters overpredict the observed SZ fluxes from Planck (Planck Collaboration XI. 2011), ACT (Sehgal et al. 2013), and SPT (Saro et al. 2017).

Question: where does the mismatch come from?

Motivation: We target the most massive maxBCG clusters as the mismatch exists in all richness bins. These clusters should have the strongest X-ray and SZ signals. It is natural to study them directly to examine the reasons for the mismatch. There are 38 clusters in the two richest bins.

X-ray: 31 from archive Chandra/XMM, 7 from XMM proposal (PI: Sun).Opitcal: maxBCG (Koester et al. 2007) and redMaPPer (Rykoff et al. 2014).

Chong Ge1, Andrea Morandi1, Ming Sun1, Eduardo Rozo2, Neelima Sehgal3, Alexey Vikhlinin4, William Forman4, Christine Jones4, and Daisuke Nagai5

X-ray scaling relations from a complete sample of the richest maxBCG clusters (arXiv:1803.05007)

1Univ. of Alabama in Huntsville, 2Univ. of Arizona, 3Stony Brook Univ., 4Harvard-Smithsonian Center for Astrophysics, 5Yale Univ.

Arnaud+10 & Rozo+09

Data

a b

c d

e f

REFERENCES

Miscentering Projection

True cluster mass galaxiesICM

hydrostaticmass

weak-lensingmassmass bias

mass bias

Arnaud+10 & Rozo+09

Planck Collaboration XI. 2011

Sehgal et al. 2013

R=Relaxed, M=Miscentering, P=Projection

chong.ge@uah.edu

SnowCluster, Snowbird, Utah, March 18-23, 2018

38 cluters