Relativistic Thermal Bremsstrahlung Gaunt Factor for the Intracluster   Plasma. III. Frequency Integrated Emissivity
  We present accurate analytic fitting formulae for the frequency integrated Gaunt factors for the relativistic as well as nonrelativistic thermal bremsstrahlung which is relevant to the intracluster plasma. The fitting is carried out for 1 =< Zj =< 28, 6.0 < log T < 8.5, where Zj is the charge number of the ion, and T is the electron temperature in kelvins. The present analytic fitting formulae will be useful for the analysis of the X-ray emission which comes from the intracluster plasma as well as the other X-ray sources. 
Naoki Itoh, Shugo Kusano, Tsuyoshi Sakamoto and Satoshi Nozawa