Study Finds Pairwise Kinematic Sunyaev-Zel'dovich Effect Robust Against Optical Selection Bias
A new study accepted by Astronomy & Astrophysics finds that optical cluster selection bias does not significantly affect pairwise kinematic Sunyaev-Zel'dovich (kSZ) measurements, with no meaningful bias detected on pairwise kSZ signals, velocities, or optical depth. The kSZ effect is used to trace cosmic growth by measuring pairwise motion between galaxy clusters and the gas within them, but line-of-sight structures can introduce systematic errors when clusters are selected optically rather than by mass. This result suggests the kSZ effect is a reliable cosmological probe even when using optically selected cluster catalogs, unlike cluster abundance and weak lensing measurements which are more susceptible to such biases.
Researchers have tested whether optical cluster selection bias — a known systematic effect in cosmological analyses — contaminates pairwise kinematic Sunyaev-Zel'dovich (kSZ) measurements. The kSZ effect probes cosmic structure growth by measuring pairwise motions of galaxy groups and clusters and the gas content within them. Selection bias arises because line-of-sight structures can simultaneously inflate optical observables like cluster richness and the cosmological signal, creating a spurious correlation at fixed cluster mass. This bias has been implicated in the tension between DES-Y1 results and Planck cosmological constraints for observables such as cluster abundance and weak lensing. Using hydrodynamical simulations with a cylindrical-volume mock richness method calibrated to DES-Y1, the authors compared optically selected clusters to mass-selected halos across a wide range of galaxy-selection criteria. They found no significant bias on pairwise kSZ signals, pairwise velocities, or optical depth within uncertainty limits of approximately 16, 10, and 8 percent, respectively. The findings indicate that pairwise kSZ measurements are more robust to this systematic than other cosmological cluster observables.
What's missing
The study's uncertainty limits (approximately 16, 10, and 8 percent for kSZ signals, pairwise velocities, and optical depth, respectively) are relatively broad, leaving open the possibility that smaller biases exist below the detection threshold. The analysis relies on hydrodynamical simulations, and it remains to be tested whether results hold for all simulation codes or baryonic feedback prescriptions.
What different sources said
- arXiv astro-phCenter
Robustness of pairwise kinematic Sunyaev-Zel'dovich effect to optical-cluster-selection bias
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