Break the one-halo–two-halo degeneracy in tSZ profiles

Obtain reliable estimates of the one-halo and two-halo contributions to the stacked thermal Sunyaev–Zel’dovich profiles of the DESI luminous red galaxy, Bright Galaxy Survey, and eROMaPPer samples by improving the treatment of foreground contamination and acquiring well-constrained measurements at large radii.

Background

The forward model separates the stacked tSZ signal into a one-halo contribution from the central object and a two-halo contribution from surrounding halos. These components are strongly degenerate, and the degeneracy is primarily broken by measurements at large aperture radii.

The paper cannot reliably fit the individual components because dust and other contaminants suppress or destabilize the large-scale measurements. Improved large-radius measurements and better contaminant handling are therefore required to determine the two-halo correction, which affects the inferred tSZ signal.

References

We have attempted to extract fits of the one-halo and two-halo contribution from these profiles, but due to the aforementioned variation in Compton- $y$ at large scales with the different map products, we are unable to obtain reliable estimates for the two-halo effect, which biases our measurements high.

— 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 Section IV.E and Conclusion, Section VI