A good textbook is Van der Ziel: Noise, from ~1980. Certainly there is a lot of newer books, too.
Attenuator noise power is usually defined as noise temperature, taken from the basic formula Pn = kTB. So, T =Pn/(kB)
S22 is a measure of impedance matching to a transmission line.
A noise temperature from a matched resistor is equal to its physical temperature. For an attenuator having a loss L (times, not dB),we have
T= To (1-1/L), where To is the ambient temperature (Kelvins).
For a 3-dB attenuator, L=2, so the output temperature T = 1/2 To.
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And for L>20, T ~ To