  We explore the effects of active galactic nuclei (AGN) and star formation
activity on the infrared (0.3-1000 microns) spectral energy distributions of
luminous infrared galaxies from z = 0.5 to 4.0. We have compiled a large sample
of 151 galaxies selected at 24 microns (S24 > 100 uJy) in the GOODS-N and ECDFS
fields for which we have deep Spitzer IRS spectroscopy, allowing us to
decompose the mid-IR spectrum into contributions from star formation and AGN
activity. A significant portion (~25%) of our sample is dominated by an AGN in
the mid-IR. Based on the mid-IR classification, we divide our full sample into
four sub-samples: z~1 star-forming (SF) sources; z~2 SF sources; AGN with clear
9.7 micron silicate absorption; and AGN with featureless mid-IR spectra. From
our large spectroscopic sample and wealth of multi-wavelength data, including
deep Herschel imaging at 100, 160, 250, 350, and 500 microns, we use 95
galaxies with complete spectral coverage to create a composite spectral energy
distribution (SED) for each sub-sample. We then fit a two-temperature component
modified blackbody to the SEDs. We find that the IR SEDs have similar cold dust
temperatures, regardless of the mid-IR power source, but display a marked
difference in the warmer dust temperatures. We calculate the average effective
temperature of the dust in each sub-sample and find a significant (~20 K)
difference between the SF and AGN systems. We compare our composite SEDs to
local templates and find that local templates do not accurately reproduce the
mid-IR features and dust temperatures of our high redshift systems. High
redshift IR luminous galaxies contain significantly more cool dust than their
local counterparts. We find that a full suite of photometry spanning the IR
peak is necessary to accurately account for the dominant dust temperature
components in high redshift IR luminous galaxies.
