Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aipc..848..471c&link_type=abstract
RECENT ADVANCES IN ASTRONOMY AND ASTROPHYSICS: 7th International Conference of the Hellenic Astronomical Society. AIP Conferenc
Astronomy and Astrophysics
Astrophysics
Active And Peculiar Galaxies And Related Systems, X-Ray Sources, X-Ray Bursts
Scientific paper
We review recent studies of X-ray spectral evolution of active galactic nuclei (AGN). One of the goals of these studies is to search for changes of the X-ray spectral properties of AGN that might have accompanied the significant evolution of the luminosity functions and the space densities of AGN recently found in optical and X-ray surveys of these objects. Determining the evolution of the spectra of AGN is commonly carried out by searching for correlations between the X-ray power-law photon indices, the optical-to-X-ray spectral slopes, and the accretion efficiencies of AGN with redshift. No significant changes in the X-ray emission properties of AGN are detected in most current studies, however, a recent survey of z > 1.5 lensed AGN indicates a possible change of accretion efficiency with redshift. Several observations of high redshift broad absorption line quasars and narrow line type-I quasars indicate the presence of massive relativistic outflows. It is proposed that these winds in combination with outflows produced by supernovae might be important in driving the evolution of the space density of AGN.
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