Query : 2006A&A...451..443M

2006A&A...451..443M - Astronomy and Astrophysics, volume 451, 443-456 (2006/5-4)

Active galactic nuclei in the mid-IR. Evolution and contribution to the cosmic infrared background.


Abstract (from CDS):

We study the evolution of the luminosity function (LF) of type-1 and type-2 Active Galactic Nuclei (AGN) in the mid-infrared, derive the contribution of the AGN to the Cosmic InfraRed Background (CIRB) and the expected source counts to be observed by Spitzer at 24µm. We used a sample of type-1 and type-2 AGN selected at 15µm (ISO) and 12µm (IRAS), and classified on the basis of their optical spectra. Local spectral templates of type-1 and type-2 AGN have been used to derive the intrinsic 15µm luminosities. We adopted an evolving smooth two-power law shape of the LF, whose parameters have been derived using an un-binned maximum likelihood method. We find that the LF of type-1 AGN is compatible with a pure luminosity evolution (L(z)=L(0)(1+z)kL_^) model where kL∼2.9. A small flattening of the faint (L15<L*15) slope of the LF with increasing redshift is favoured by the data. A similar evolutionary scenario is found for the type-2 population with a rate kL ranging from ∼1.8 to 2.6, depending significantly on the adopted mid-infrared spectral energy distribution. For type-2 AGN a flattening of the LF with increasing redshift is suggested by the data, possibly caused by the loss of a fraction of type-2 AGN hidden within the optically classified starburst and normal galaxies. The type-1 AGN contribution to the CIRB at 15µm is (4.2-12.1)x10–11W/m2/sr, while the type-2 AGN contribution is (5.5-11.0)x10–11 W/m2/sr. We expect that Spitzer will observe, down to a flux limit of S_24µ m_=0.01mJy, a density of ∼1200deg–2 type-1 and ∼1000deg–2 type-2 optically classified AGN. AGN evolve in the mid-infrared with a rate similar to the ones found in the optical and X-rays bands. The derived total contribution of the AGN to the CIRB (4-10%) and Spitzer counts should be considered as lower limits, because of a possible loss of type-2 sources caused by the optical classification.

Abstract Copyright:

Journal keyword(s): cosmology: observations - infrared: galaxies - galaxies: active - surveys - galaxies: evolution

Simbad objects: 6

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Number of rows : 6
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 ELAIS S1 reg 00 34 44 -43 28.2           ~ 176 0
2 M 77 GiP 02 42 40.7091669408 -00 00 47.859690204 9.70 9.61 8.87 10.1 9.9 ~ 4322 2
3 ELAIS S2 reg 05 02 24 -30 35.9           ~ 18 0
4 NAME Hubble Deep Field reg 12 36 49.5 +62 12 58           ~ 1873 1
5 NAME Circinus Galaxy Sy2 14 13 09.906 -65 20 20.47   10.89 9.84 10.6 10.0 ~ 1093 2
6 NAME HDF-S reg 22 32 56 -60 33.0           ~ 553 0

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