Soft X-ray spectroscopy of Compton-thick Seyfert 2 galaxies with BeppoSAX

We present an X-ray spectroscopic study of the bright Compton-thick Seyfert 2 galaxies NGC 1068 and the Circinus Galaxy, performed with BeppoSAX. Matt et al. interpreted the spectrum above 4 keV as the superposition of Compto n reflection and warm plasma scattering of the nuclear radiation. When this continuum is extrapolated downwards to 0.1 keV, further components arise. The NGC 1068 spectrum is rich in emission lines, mainly owing to K-alpha tr ansitions of He-like elements from oxygen to iron, plus a K-alpha fluoresce nt line from neutral iron. If the ionized lines originate in the warm scatt erer, its thermal and ionization structure must be complex. From the contin uum and line properties, we estimate a column density, N-warm, of the warm scatterer less than a few x 10(21) cm(-2). In the Circinus Galaxy, the abse nce of highly ionized iron is consistent with a scattering medium with U-X less than or similar to 5 and N-warm similar to a few x 10(22) cm(-2). In b oth cases the neutral iron line is most naturally explained as fluorescence in the medium responsible for the Compton reflection continuum. In NGC 106 8 an optically thin plasma emission with kT similar or equal to 500 eV and strongly sub-solar metallicity is required, while such a component is only marginal in the Circinus Galaxy. We tentatively identify this component as emission of diffuse hot gas in the nuclear starbursts. Possible causes for the metal depletion are discussed.