Hard X-ray emission from massive star clusters in a giant molecular cloud NGC 6334

We report on detection with the ASCA satellite of hard X-rays from far infr ared (FIR) star clusters in the giant molecular cloud (GMC) cores of the NG C 6334 star-forming region. Five FIR cores are visible in the hard X-ray ba nd (E > 2 keV), while in the soft X-ray band (E <2 keV) the emission is abs orbed, except for one core. The observed spectra can be fitted with thermal emission from a hot plasma, whose temperature of <similar to> 9 keV is sig nificantly higher than those reported of low-mass Class I pre-main-sequence stars (PMSs) (similar to 3 keV) in nearby dark clouds and those of OB-type main-sequence stars (similar to 1 keV). The X-ray luminosity of each core is typically 10(33) erg s(-1) or 10(3) times that of typical low-mass PMSs. The observed hard X-rays may be emitted from young massive stars and loss- mass/intermediate-mass PMSs in the FIR cores. The observed hard X-ray flux can ionize the inner part (tau similar to 0.3 pc) of the GMC cores at a rat e comparable to that by cosmic-ray particles. If the L-X/M ratio of similar to 10(-5)L./M. observed in NGC 6334 is typical among GMCs, the X-ray flux from all GMCs in the Galaxy (similar to 10(9) M.) can account for about 20% of the diffuse galactic ridge hard X-ray emission.