Far-Infrared Characterization of an Ultraluminous Starburst Associated with a Massively Accreting Black Hole at z = 1.15

As part of the All-Wavelength Extended Groth Strip International Survey (AEGIS), we describe the panchromatic characterization of an X-ray-luminous active galactic nucleus (AGN) in a merging galaxy at z = 1.15. This object is detected at infrared (8, 24, 70, and 160 μm), submillimeter (850 μm), and radio wavelengths, from which we derive a bolometric luminosity Lbol ~ 9 × 1012 L☉. We find that the AGN clearly dominates the hot dust emission below 40 μm but its total energetic power inferred from the hard X-rays is substantially less than the bolometric output of the system. About 50% of the infrared luminosity is indeed produced by a cold dust component that probably originates from enshrouded star formation in the host galaxy. In the context of a coeval growth of stellar bulges and massive black holes, this source might represent a "transition" object, sharing properties with both quasars and luminous starbursts. Study of such composite galaxies will help address how the star formation and disk-accretion phenomena may have regulated each other at high redshift and how this coordination may have participated in the buildup of the relationship observed locally between the masses of black holes and stellar spheroids.