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Where Do Obscured AGN Fit in the Galactic Timeline?

Presentation #337.15 in the session “AGN and Quasars 2”.

Published onJan 11, 2021
Where Do Obscured AGN Fit in the Galactic Timeline?

X-ray bright active galactic nuclei (AGN) are predicted to follow an extended stage of obscured black hole growth, after which they produce most of their feedback.  In support of this picture we examine the X-ray undetected AGN in the COSMOS field and compare their host galaxies with X-ray bright AGN. We examine galaxies with M>109.5Mꙩ for the presence of AGN at redshifts z = 0.5 - 3.  We select AGN in the infrared using Spitzer and Herschel and correlate different infrared selection techniques to assess their reliability. These IR colors allow us to select AGN within strongly star forming host galaxies.  Of galaxies investigated, over 60% reveal evidence of dust heating surrounding super-massive black holes, but lack an X-ray detection. We X-ray stack Chandra observations of these galaxies to obtain hard and soft fluxes, allowing us to measure the energetics of these AGN. Stacking allows us to determine obscuration and X-ray luminosities to calculate accretion rates. We demonstrate that both low luminosity AGN and obscured AGN are responsible for IR emission in X-ray undetected galaxies. We find a clear correlation between X-ray luminosity and IR AGN luminosity in the stacked galaxies. Finally, we find that X-ray undetected AGN all lie on the main sequence, regardless of mass or redshift. This work demonstrates that there is a higher population of obscured AGN than previously thought.  Our results fit in with the paradigm where obscured AGN directly proceed an unobscured phase, this unobscured phase is followed by quenching of star formation.

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