Mathematics – Logic
Scientific paper
Jul 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...294..486r&link_type=abstract
Astrophysical Journal, Vol.294, NO. 2/JUL15, P. 486, 1985
Mathematics
Logic
36
Scientific paper
Galaxy mergers may produce active galactic nuclei (AGNs) by repopulating stellar loss-cone orbits around a central black hole. In the companion paper we derived a local bolometric luminosity function of AGNs based on this process. In this paper we interpret the observed cosmological evolution of the luminosity function of AGNs as due to evolution of the merging rate among galaxies after their formation at a redshift of ˜ 3. An important difference between our model and previous (empirical) models is that the evolution depends on galactic (stellar) luminosity instead of central nonthermal luminosity. The radio counts at 1.4 GHz and optical counts are reproduced by the model if the merging rate of the galaxies at the bright end of the galaxy luminosity function evolves considerably faster than the merging rate of the smaller galaxies. The theoretical and observed luminosity functions at high redshift have similar characteristics: (i) at high luminosity the evolution is best described by luminosity evolution, and (2) the luminosity function has a maximum at ˜1O3 Gpc-3 , which is the space density of the most massive galaxies. A large fraction of these galaxies are presumably formed in the precursors of rich clusters. Their merger rate is high initially and declines rapidly on a time scale of a few billion years. If the initial density fluctuation spectrum for protoclusters of mass Mcl has the form δρ/ρ ∝ Mcl-(1+n)3/2 , then the steep evolution of the most luminous galaxies suggests n≈ -1.3 at a redshift of ˜ 3, which is consistent with the observed clustering of galaxies. Numerical experiments of an expanding universe indicate that outside rich clusters the merger rate evolves approximately as (cosmic time)-1, which seems consistent with the mild evolution of the smaller galaxies having a lower mean central luminosity.
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