X-QUEST: A Comprehensive X-ray Study of Local ULIRGs and QSOs
  We present results from the X-ray portion of a multi-wavelength study of
local ULIRGs and QSOs called QUEST (Quasar-ULIRG Evolution STudy). The data
consist of new and archival X-ray data on 40 ULIRGs and 26 PG QSOs taken with
Chandra and XMM-Newton. A combination of traditional and hardness ratio
spectral fitting methods is used to characterize the X-ray properties of these
objects. The absorption-corrected 2-10 keV to bolometric luminosity ratios of
the ULIRGs and PG QSOs suggest that the likelihood for dominant nuclear
activity increases along the merger sequence from "cool" ULIRGs, "warm" ULIRGs,
infrared-bright QSOs, and infrared-faint QSOs. The starburst dominates the
total power in ULIRGs prior to the merger, and this is followed by rapid black
hole growth during and after coalescence. These results are in general
agreement with those obtained in the mid-infrared with Spitzer and recent
numerical simulations.
