New BeppoSAX observations of the nearby archetypical starburst galaxies ( SBGs ) NGC253 and M82 are presented .
The main observational result is the unambiguous evidence that the hard ( 2-10 keV ) component is ( mostly ) produced in both galaxies by thermal emission from a metal-poor ( \sim 0.1–0.3 solar ) , hot ( kT \sim 6– 9 keV ) and extended ( see companion paper : Cappi et al .
1998 ) plasma .
Possible origins of this newly discovered component are briefly discussed .
A remarkable similarity with the ( Milky Way ) Galactic Ridge ’ s X-ray emission suggests , nevertheless , a common physical mechanism .