Spitzer number counts of active galactic nuclei in the goods fields
We present mid-infrared observations of active galactic nuclei (AGNs) in the GOODS fields, performed with the âˆ¼Spitzer Space Telescope. These are the deepest infrared and X-ray fields to date and cover a total area of âˆ¼0.1 deg2. âˆ¼AGNs are selected on the basis of their hard (2-8 keV) X-ray emission. The median AGN infrared luminosity is at âˆ¼least 10 times larger than the median for normal galaxies with the same redshift distribution, suggesting that the âˆ¼infrared emission is dominated by the central nucleus. The X-ray-to-infrared luminosity ratios of GOODS AGNs, âˆ¼most of which are at 0.5 â‰¤ z â‰¤ 1.5, are similar to the values obtained for AGNs in the local universe. The observed âˆ¼infrared flux distribution has an integral slope of âˆ¼ 1.5, and there are 1000 sources per square degree brighter than âˆ¼50 Î¼Jy at âˆ¼3-6 Î¼m. The counts approximately match the predictions of models based on AGN unification, in âˆ¼which the majority of AGNs are obscured. This agreement confirms that the faintest X-ray sources, which are âˆ¼dominated by the host galaxy light in the optical, are obscured AGNs. Using these Spitzer data, the AGN contribution âˆ¼to the extragalactic infrared background light is calculated by correlating the X-ray and infrared catalogs. This is âˆ¼likely to be a lower limit given that the most obscured AGNs are missed in X-rays. We estimate the contribution of âˆ¼AGNs missed in X-rays, using a population synthesis model, to be âˆ¼45% of the observed AGN contribution, making âˆ¼the AGN contribution to the infrared background at most âˆ¼2%-10% in the 3-24 Î¼m range, depending on wavelength, lower than most previous estimates. The AGN contribution to the infrared background remains roughly âˆ¼constant with source flux in the IRAC bands but decreases with decreasing flux in the MIPS 24 Î¼m band, where the âˆ¼galaxy population becomes more important. Â© 2006. The American Astronomical Society. All rights reserved.
|Título según WOS:||Spitzer number counts of active galactic nuclei in the goods fields|
|Título según SCOPUS:||Spitzer number counts of active galactic nuclei in the goods fields|
|Título de la Revista:||ASTROPHYSICAL JOURNAL|
|Editorial:||IOP PUBLISHING LTD|
|Fecha de publicación:||2006|
|Página de inicio:||603|