The Merger-Triggered Active Galactic Nuclei Contribution to the
  Ultraluminous Infrared Galaxy Population
  It has long been thought that there is a connection between ultraluminous
infrared galaxies (ULIRGs), quasars, and major mergers. Indeed, simulations
show that major mergers are capable of triggering massive starbursts and
quasars. However, observations by the Herschel Space Observatory suggest that,
at least at high redshift, there may not always be a simple causal connection
between ULIRGs and mergers. Here, we combine an evolving merger-triggered AGN
luminosity function with a merger-triggered starburst model to calculate the
maximum contribution of major mergers to the ULIRG population. We find that
major mergers can account for the entire local population of ULIRGs hosting AGN
and ~25% of the total local ULIRG luminosity density. By z ~ 1, major mergers
can no longer account for the luminosity density of ULIRGs hosting AGN and
contribute \lesssim 12% of the total ULIRG luminosity density. This drop is
likely due to high redshift galaxies being more gas rich and therefore able to
achieve high star formation rates through secular evolution. Additionally, we
find that major mergers can account for the local population of warm ULIRGs.
This suggests that selecting high redshift warm ULIRGs will allow for the
identification of high redshift merger-triggered ULIRGs. As major mergers are
likely to trigger very highly obscured AGN, a significant fraction of the high
redshift warm ULIRG population may host Compton thick AGN.
