We present Keck spectroscopic observations and redshifts for a sample of
767 Herschel-SPIRE selected galaxies (HSGs) at 250, 350, and 500 μm,
taken with the Keck I Low Resolution Imaging Spectrometer and the Keck
II DEep Imaging Multi-Object Spectrograph. The redshift distribution of
these SPIRE sources from the Herschel Multitiered Extragalactic Survey
peaks at z = 0.85, with 731 sources at z <2 and a tail of sources
out to z ~ 5. We measure more significant disagreement between
photometric and spectroscopic redshifts (langΔz/(1 + z
spec)rang = 0.29) than is seen in non-infrared selected
samples, likely due to enhanced star formation rates and dust
obscuration in infrared-selected galaxies. The infrared data are used to
directly measure integrated infrared luminosities and dust temperatures
independent of radio or 24 μm flux densities. By probing the dust
spectral energy distribution (SED) at its peak, we estimate that the
vast majority (72%-83%) of z <2 Herschel-selected galaxies would
drop out of traditional submillimeter surveys at 0.85-1 mm. We find that
dust temperature traces infrared luminosity, due in part to the SPIRE
wavelength selection biases, and partially from physical effects. As a
result, we measure no significant trend in SPIRE color with redshift; if
dust temperature were independent of luminosity or redshift, a trend in
SPIRE color would be expected. Composite infrared SEDs are constructed
as a function of infrared luminosity, showing the increase in dust
temperature with luminosity, and subtle change in near-infrared and
mid-infrared spectral properties. Moderate evolution in the far-infrared
(FIR)/radio correlation is measured for this partially radio-selected
sample, with q IRvprop(1 + z)-0.30 ±
0.02 at z <2. We estimate the luminosity function and implied
star formation rate density contribution of HSGs at z <1.6 and find
overall agreement with work based on 24 μm extrapolations of the
LIRG, ULIRG, and total infrared contributions. This work significantly
increased the number of spectroscopically confirmed infrared-luminous
galaxies at z Gt 0 and demonstrates the growing importance of dusty
starbursts for galaxy evolution studies and the build-up of stellar mass
throughout cosmic time.