The redshift sequence of AGNs

AGN are now detected with ground-based telescopes all the way to z ~ 7. This is done by observing thousands of sources discovered by large surveys like SDSS and 2DF. Arranging the objects according to their redshift, like in Figure 9.1, clearly shows the redshift progression of absorption by intergalactic neutral hydrogen starting at an observed wavelength of (1 + z)1215 Å. At z = 7, this is close to the long wavelength limit of ground-based spectroscopy. Detailed study of such sources, and measurement of their mass and accretion rate, can be used to follow BH evolution through cosmic time and to compare it with the evolution of dark matter halos and galaxies. The main tools that are used for this study are the luminosity and mass functions of AGNs. Before investigating these functions, we review, briefly, some aspects of galaxy evolution.

Highlights of galaxy evolution

Hierarchical structure formation

The most successful cosmological model of today is the Λ cold dark matter (ACDM) model with its three ingredients: dark energy, dark matter, and bary-onic matter. Support for this model comes from measurements of the acceleration of the universe, from observations of the cosmic microwave background (CMB), from the abundance of the light elements, and from several other observations. The success of the model in explaining the observed temperature fluctuations at the recombination era, about 380,000 years after the Big Bang, when the radiation and baryon fluids stopped interacting with each other, is perhaps its main strength.