Where Do Obscured AGN Fit in a Galaxy's Timeline?
Giavalisco, Mauro; Kirkpatrick, Allison; Ji, Zhiyuan; Lambrides, Erini; Hatcher, Cassandra; Carroll, Christopher M.; Civano, Francesca; Fornasini, Francesca; Kocesvski, Dale; Hickox, Ryan
United States
Abstract
Many X-ray bright active galactic nuclei (AGNs) are predicted to follow an extended stage of obscured black hole growth. In support of this picture we examine the X-ray undetected AGNs in the COSMOS field and compare their host galaxies with X-ray bright AGNs. We examine galaxies with M* > 109.5 M⊙ for the presence of AGNs at redshifts z = 0.5-3. We select AGNs in the infrared using Spitzer and Herschel detections and use color selection techniques to select AGNs within strongly star-forming hosts. We stack Chandra X-ray data of galaxies with an infrared (IR) detection but lacking an X-ray detection to obtain soft and hard fluxes, allowing us to measure the energetics of these AGNs. We find a clear correlation between X-ray luminosity and IR AGN luminosity in the stacked galaxies. We also find that X-ray undetected AGNs all lie on the main sequence-the tight correlation between the star formation rate and M* that holds for the majority of galaxies, regardless of mass or redshift. This work demonstrates that there is a higher population of obscured AGNs than previously thought.