2004/01/14 by N. Menci, F. Fiore, G. C. Perola +1 · 3 citations
Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Cosmic ray #Cosmic time #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Luminosity #Physics #Redshift #X-ray background #astro-ph
paper · pdf · doi:10.1086/382780
published as Astrophys.J. 606 (2004) 58-66 · 27 pages, accepted for publication in ApJ
arxiv created 2004/01/14 · openalex publication_date 2004/04/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
We have incorporated the description of the X-ray properties of active galactic nuclei (AGNs) into a semianalytic model of galaxy formation, adopting physically motivated scaling laws for accretion triggered by galaxy encounters. Our model reproduces the level of the cosmic X-ray background at 30 keV; we predict that the largest contribution (around two-thirds) comes from sources with intermediate X-ray luminosity 10 43.5 < L X /ergs s -1 < 10 44.5 , with 50% of the total specific intensity produced at z < 2. The predicted number density of X-ray-luminous AGNs ( L X > 10 44.5 ergs s -1 in the 2-10 keV band) peaks at z ≈ 2, with a decline of around 3 dex to z = 0; for the low-luminosity sources (10 43 < L X /ergs s -1 < 10 44 ), it has a broader and less pronounced maximum around z ≈ 1.5. The comparison with the data shows a generally good agreement. The model predictions slightly exceed the observed number of low-luminosity AGNs at z ~ 1.5, with the discrepancy progressively extending to intermediate-luminosity objects at higher redshifts; we discuss possible origins of the mismatch. Finally, we predict the source counts and the flux distribution at different redshifts in the hard (20-100 keV) X-ray band for the sources contributing to the X- ray background.