Computer Science
Scientific paper
Jul 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003hst..prop.9869m&link_type=abstract
HST Proposal ID #9869
Computer Science
Hst Proposal Id #9869 Agn/Quasars
Scientific paper
Chandra has resolved most of the > 2 keV X-ray background {XRB} into discrete sources. Ground-based optical studies of these sources have revealed a substantial population of apparently normal galaxies at modest redshift, not the Seyfert 2 galaxies predicted by models for the origin of the XRB. These objects have X-ray spectral properties and luminosities similar to Seyfert 2s, but emission lines are weak or absent in their starlight-dominated optical spectra, suggesting the emergence of a new class of obscured or gas-poor AGNs at moderate redshifts. However, most of the galaxies in question are distant enough that their angular sizes are comparable to the slit widths used in ground-based spectroscopic observations. Thus, it is possible that these "normal" galaxies are classical Seyfert 2s whose nuclear spectral features have been overwhelmed {"hidden"} by host galaxy light. The high angular resolution of HST/STIS offers a unique opportunity to isolate the nuclei of these objects spatially. STIS spectra of a small, carefully selected sample of optically "normal" X-ray galaxies will help clarify the origin of the XRB, which is vital for understanding the growth of supermassive black holes in galactic nuclei.
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