X-RAY-EMISSION FROM STARBURST GALAXIES

We report the results of an investigation of X-ray emission from a sample of 53 IRAS-selected candidate starburst galaxies. Superposed soft and hard X-ray emission from these galaxies in the Einstein IPC and HEAO 1 A-2 and A-4 energy bands, which span 0.5 to 160 keV, is detected at the 99.6% confidence level, after allowing for confusion noise in the HEAO 1 data. Above 15 keV the confidence level is 97%. The combined spectrum is flat, with a (photon) power-law index of 1.0 +/- 0.3. The contribution of the population of sources represented by this sample to the 3-50 keV residual cosmic X-ray background is estimated to be at least approximately 4% assuming no evolution. Moderate evolution, for which there is some observational evidence, increases this fractional contribution to approximately 26%.