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Unveiling a Population of X-ray Non-Detected AGN

J. L. Donley·G. H. Rieke·J. R. Rigby·P. G. Perez-Gonzalez
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Abstract

We define a sample of 27 radio-excess AGN in the Chandra Deep Field North by selecting galaxies that do not obey the radio/infrared correlation for radio-quiet AGN and star-forming galaxies. Approximately 60% of these radio-excess AGN are X-ray undetected in the 2 Ms Chandra catalog, even at exposures of > 1 Ms; 25% lack even 2-sigma X-ray detections. The absorbing columns to the faint X-ray-detected objects are 10^22 cm^-2 < N_H < 10^24 cm^-2, i.e., they are obscured but unlikely to be Compton thick. Using a local sample of radio-selected AGN, we show that a low ratio of X-ray to radio emission, as seen in the X-ray weakly- and non-detected samples, is correlated with the viewing angle of the central engine, and therefore with obscuration. Our technique can explore the proportion of obscured AGN in the distant Universe; the results reported here for radio-excess objects are consistent with but at the low end of the overall theoretical predictions for Compton-thick objects.

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J. L. Donley, G. H. Rieke, J. R. Rigby, P. G. Perez-Gonzalez. 2005-07-28. Unveiling a Population of X-ray Non-Detected AGN. https://doi.org/10.1086/491668

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