Euclid Preparation: TBD. the Impact of Line-of-sight Projections on the Covariance Between Galaxy Cluster Multi-Wavelength Observable Properties – Insights from Hydrodynamic Simulations

Euclid Collaboration,A. Ragagnin，D. Vergani,G. Verza

Astronomy &amp Astrophysics（2025）

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Abstract

Cluster cosmology can benefit from combining multi-wavelength studies, which can benefit from characterising the correlation coefficients between different mass-observable relations. In this work, we aim to provide information on the scatter, the skewness, and the covariance of various mass-observable relations in galaxy clusters in cosmological hydrodynamic simulations. This information will help future analyses to better tackle accretion histories and projection effects and model mass observable relations for cosmology studies.We identify galaxy clusters in Magneticum Box2b simulations with mass M_ 200c>10^14 M_⊙ at redshift z=0.24 and z=0.90. Our analysis includes -derived properties such as richness, stellar mass, lensing mass, and concentration. Additionally, we investigate complementary multi-wavelength data, including X-ray luminosity, integrated Compton-y parameter, gas mass, and temperature. The impact of projection effects on mass-observable residuals and correlations is then examined. At intermediate redshift (z=0.24), projection effects impact lensing concentration, richness, and gas mass the most in terms of scatter and skewness of log-residuals of scaling relations. The contribution of projection effects can be significant enough to boost a spurious hot- vs. cold-baryons correlation and consequently hide underlying correlations due to halo accretion histories. At high redshift (z=0.9), the richness has a much lower scatter (of log-residuals), and the quantity that is most impacted by projection effects is the lensing mass. Lensing concentration reconstruction, in particular, is affected by deviations of the reduced-shear profile shape from the one derived by an NFW profile rather than interlopers in the line of sight.

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【要点】：本研究通过宇宙 hydrodynamic 模拟，分析了不同波长下观测到的星系团质量-可观测量之间的散射、偏斜和协方差，探讨了视线投影效应对质量-可观测量残差和相关性影响。

【方法】：利用 Magneticum Box2b 模拟，在红移 z=0.24 和 z=0.90 下，识别质量大于 10^14 M_⊙ 的星系团，分析其丰富度、恒星质量、透镜质量和浓度等衍生属性，以及 X 射线亮度、积分 Compton-y 参数、气体质量和温度等多波长数据。

【实验】：研究显示在中间红移（z=0.24）时，投影效应对透镜浓度、丰富度和气体质量的散射和偏斜影响最大；在高质量（z=0.9）时，丰富度散射较低，透镜质量受投影效应影响最大，尤其是透镜浓度重建受到由 NFW 轮廓形状偏差而非视线中的前景物体影响。

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