Integrated Compton parameter ($Y=\int yd\Omega$)

For a source at angular diameter distance $D_A$,The quantity $Y{D}_A^2$ measures volume-integrated electron pressure, hence thermal energy up to a known ideal-gas factor. The redshift independence of the thermal SZ distortion's surface brightness does not make $Y$ distance independent. Angular integration region, beam convolution, temperature structure and cluster geometry matter when comparing measurements and mass proxies.