= Integrated Compton parameter
{title2=$Y=\int y\,d\Omega$}
For a source at <angular diameter distance> $D_A$,
$$
Y=\frac{\sigma_T}{m_ec^2D_A^2}\int P_e\,dV.
$$
The quantity $YD_A^2$ 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.
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