  We present preliminary results on 24micron detections of luminous infrared
galaxies at z>1 with the Multiband Imaging Photometer for Spitzer (MIPS).
Observations were performed in the Lockman Hole and the Extended Groth Strip
(EGS), and were supplemented by data obtained with the Infrared Array Camera
(IRAC) between 3 and 9microns. The positional accuracy of ~2arcsec for most
MIPS/IRAC detections provides unambiguous identifications of their optical
counterparts. Using spectroscopic redshifts from the Deep Extragalactic
Evolutionary Probe survey, we identify 24micron sources at z>1 in the EGS,
while the combination of the MIPS/IRAC observations with $BVRIJHK$ ancillary
data in the Lockman Hole also shows very clear cases of galaxies with
photometric redshifts at 1<z<2.5.
  The observed 24micron fluxes indicate infrared luminosities greater than
10^11 L_sol, while the data at shorter wavelengths reveal rather red and
probably massive (M>=M*) galaxy counterparts. It is the first time that this
population of luminous objects is detected up to z~2.5 in the infrared. Our
work demonstrates the ability of the MIPS instrument to probe the dusty
Universe at very high redshift, and illustrates how the forthcoming Spitzer
deep surveys will offer a unique opportunity to illuminate a dark side of
cosmic history not explored by previous infrared experiments.
