Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-04-07
Astronomy and Astrophysics
Astrophysics
14 pages, 5 figures to appear in "Carnegie Observatories Astrophysics Series, Vol. 1: Coevolution of Black Holes and Galaxies,
Scientific paper
Most of the local active galactic nucleus (AGN) population is obscured and much of the X-ray background originates in obscured AGNs. The contribution of obscured accretion to the growth of massive black holes is discussed here. The recent identification of significant samples of the X-ray sources that dominate the X-ray background intensity has shown a redshift peak at 0.7-0.8, rather than the redshift of 2 found for bright optical quasars. Obscured accretion has a faster evolution than unobscured accretion. The lower redshift and luminosity of most obscured AGNs mean that although they dominate the absorption-corrected intensity of the X-ray background by a factor of about 3 over unobscured objects, they make only an equal contribution to the local mass density in black holes. Obscured and unobscured AGNs together contribute about 4 x 10^5 Msun/Mpc^3. Type 2 quasars and Compton-thick objects may give another 10^5 Msun/Mpc^3, but no more unless direct determinations from the M-sigma relation seriously underestimate the local black hole mass density, or unless most massive black holes are rapidly spinning (so having a higher radiative efficiency than the 10% assumed above). Obscured accretion probably dominates the growth of black holes with masses below a few times 10^8 Msun, whereas optically bright quasars dominate at higher masses. The luminosity absorbed by the dusty gas in obscured AGNs is reradiated in the mid-infrared and far-infrared bands. The contribution of AGNs drops from about 20% of the mid-infrared background to just a few percent of the far-infrared background.
No associations
LandOfFree
Obscured Active Galactic Nuclei and Obscured Accretion does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Obscured Active Galactic Nuclei and Obscured Accretion, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Obscured Active Galactic Nuclei and Obscured Accretion will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-521320