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 (8mic, 24mic, 70mic, 160mic), submillimeter (850mic) and radio wavelengths, from which we derive a bolometric luminosity L_bol ~ 9x10^12 Lsol. We find that the AGN clearly dominates the hot dust emission below 40mic 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 to the build-up of the relationship observed locally between the masses of black holes and stellar spheroids.
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