The Active Galactic Nuclei Contribution to the Mid‐Infrared Emission of Luminous Infrared Galaxies Academic Article uri icon


  • We determine the contribution of AGN to the mid-IR emission of luminous infrared galaxies (LIRGs) at z > 0.6 by measuring the mid-IR dust continuum slope of 20,039 mid-IR sources. The 24 μm sources are selected from a Spitzer MIPS survey of the NOAO Deep Wide-Field Survey Boötes field and have corresponding 8 μm data from the IRAC Shallow Survey. There is a clear bimodal distribution in the 24 to 8 μm flux ratio. The X-ray-detected sources fall within the peak corresponding to a flat spectrum in vf v, implying that it is populated by AGN-dominated LIRGs, whereas the peak corresponding to a higher 24 to 8 μm flux ratio is likely due to LIRGs whose IR emission is powered by starbursts. The 24 μm emission is increasingly dominated by AGN at higher 24 μm flux densities (f 24): the AGN fraction of the z > 0.6 sources increases from 9% at f24 ≈ 0.35 mJy to 74% ±20% at f24 ≈ 3 mJy, in good agreement with model predictions. Deep 24 μm, small-area surveys, like GOODS, will be strongly dominated by starburst galaxies. AGN are responsible for ∼3%-7% of the total 24 μm background. © 2006. The American Astronomical Society. All rights reserved.

author list (cited authors)

  • Brand, K., Dey, A., Weedman, D., Desai, V., Le Floc’h, E., Jannuzi, B. T., ... Cool, R. J.

citation count

  • 84

publication date

  • June 2006