The X-ray Spectrum of Seyfert 2s and Ultra-luminous IR Galaxies

Hagai Netzer 
Tel Aviv University and RIKEN

The X-ray spectra of AGN and active star-forming regions are characterized
by strong emission lines and a large amount of obscuration. Analysis
of the lines in Seyfer 2 galaxies suggest that there are at least two
components of highly ionized gas, possibly at different locations. This
seems to be in contradiction with the X-ray observations of Seyfert
1 galaxies.  Similar X-ray lines are also observed in several ULIRGs,
that are very luminous infrared sources powered, most probably, by
active starbursts in colliding galaxies. This raises the question of
what distinguish AGN excited gas from hot gas in star-forming regions.
X-ray emission lines provide the best diagnostics of the hot gas in the
center of both AGN and ULIRGs. High spectral resolution observations, by
the coming new X-ray missions, will enable us to evaluate the relative
contributions of collisionally heated and photoionized gas. The study
of ULIRGs with these satellites is likely to provide the first solid
evidence for accretion onto massive black holes even in sources thought
to be dominated by violent star formation.