Determine the origin and universality of y–tau scaling-relation differences

Determine whether the variation in the fitted parameters of the empirical Compton-$y$–optical-depth scaling relation among the DESI luminous red galaxy, Bright Galaxy Survey, and eROMaPPer samples is caused by differences in sample properties such as halo mass and redshift or by residual thermal SZ systematic effects.

Background

The paper derives bary−τˉbar{y}-\bar{\tau} scaling relations for three tracer samples and finds that the fitted normalization and slope differ between samples. These parameters depend on sample characteristics and may also be affected by residual contamination from dust, the cosmic infrared background, and radio sources.

The authors explicitly leave unresolved whether the observed variation reflects genuine differences in the halo populations or uncorrected measurement systematics. Resolving this issue is important for assessing whether the scaling relation is universal and transferable across CMB surveys and galaxy samples.

References

At present, it is difficult to discern whether the differences we see in the best-fit parameters are a result of differing sample properties (e.g. mass, redshift) or residual systematics.

— Optical Depths from the Thermal Sunyaev-Zel'dovich Effect with ACT DR6 and DESI DR1 Spectroscopic Galaxies and Optically-Selected Clusters  (2609.08939 - Moore et al., 8 Sep 2026) in Conclusion, Section VI

Consequently, it would be difficult to determine whether a trend with redshift, if detected, reflects true cosmic evolution or an artifact of poorly constrained profile fits at high redshift. This problem is exacerbated at lower masses, where halos are physically smaller, and the one-halo term is weaker. The redshift evolution should therefore be constrained only above a critical mass, at which the amplitude, slope, and centroid of the pressure profile can be measured meaningfully. Future mm instruments with better angular resolution will allow this threshold to be pushed to lower masses. Because such a subsample would not span the full range of mass and richness presented here, we defer this analysis to a follow-up study.

— Thermal Sunyaev-Zel'dovich Effect in the circumgalactic medium - III: does richness matter?  (2610.21628 - Das et al., 15 Oct 2026) in Section 4.5, What is the principal component?