Cluster Optical Depth
Cluster Properties
About the SZ Effect
CMB photons passing through hot galaxy cluster gas undergo inverse Compton scattering off energetic electrons, creating a characteristic spectral distortion.
- Thermal SZ (tSZ): Temperature decrement at low frequencies, increment at high frequencies
- Compton y-parameter: Measures integrated pressure along the line of sight
- Null frequency: ~217 GHz where ΔT = 0
- Cosmology: Used by ACT, SPT, Planck to find clusters and measure H₀
Typical Values
- Rich cluster: T_e ~ 8-10 keV, y ~ 10⁻⁴
- Poor group: T_e ~ 2-3 keV, y ~ 10⁻⁵
- ΔT/T at 150 GHz: typically -10⁻⁴ to -10⁻³
- Observation bands: 90, 150, 220, 270, 350 GHz