Spitzer power-law active galactic nucleus candidates in the Chandra Deep Field-North

J. L. Donley, G. H. Rieke, P. G. Pérez-González, J. R. Rigby, A. Alonso-Herrero

Research output: Contribution to journalArticlepeer-review

165 Scopus citations


We define a sample of 62 galaxies in the Chandra Deep Field-North whose Spitzer IRAC SEDs exhibit the characteristic power-law emission expected of luminous AGNs. We study the multiwavelength properties of this sample and compare the AGNs selected in this way to those selected via other Spitzer color-color criteria. Only 55% of the power-law galaxies are detected in the X-ray catalog at exposures of >0.5 Ms, although a search for faint emission results in the detection of 85% of the power-law galaxies at the ≥2.5 σ detection level. Most of the remaining galaxies are likely to host AGNs that are heavily obscured in the X-ray. Because the power-law selection requires the AGNs to be energetically dominant in the near- and mid-infrared, the power-law galaxies comprise a significant fraction of the S/Hfeer-detected AGN population at high luminosities and redshifts. The high 24 μm detection fraction also points to a luminous population. The power-law galaxies comprise a subset of color-selected AGN candidates. A comparison with various mid-infrared color selection criteria demonstrates that while the color-selected samples contain a larger fraction of the X-ray-luminous AGNs, there is evidence that these selection techniques also suffer from a higher degree of contamination by star-forming galaxies in the deepest exposures. Considering only those power-law galaxies detected in the X-ray catalog, we derive an obscured fraction of 68% (2:1). Including all of the power-law galaxies suggests an obscured fraction of <81% (4:1).

Original languageEnglish (US)
Pages (from-to)167-190
Number of pages24
JournalAstrophysical Journal
Issue number1 I
StatePublished - May 1 2007


  • Galaxies: active
  • Infrared: galaxies
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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