Near-infrared spectroscopy of 5 ultra-massive galaxies at 1.7 < z < 2.7
  We present the results of a pilot near-infrared (NIR) spectroscopic campaign
of five very massive galaxies ($\log(\text{M}_\star/\text{M}_\odot)>11.45$) in
the range of $1.7<z<2.7$. We measure an absorption feature redshift for one
galaxy at $z_\text{spec}=2.000\pm0.006$. For the remaining galaxies, we combine
the photometry with the continuum from the spectra to estimate continuum
redshifts and stellar population properties. We define a continuum redshift
($z_{\rm cont}$ ) as one in which the redshift is estimated probabilistically
using EAZY from the combination of catalog photometry and the observed
spectrum. We derive the uncertainties on the stellar population synthesis
properties using a Monte Carlo simulation and examine the correlations between
the parameters with and without the use of the spectrum in the modeling of the
spectral energy distributions (SEDs). The spectroscopic constraints confirm the
extreme stellar masses of the galaxies in our sample. We find that three out of
five galaxies are quiescent (star formation rate of $\lesssim 1
M_\odot~yr^{-1}$) with low levels of dust obscuration ($A_{\rm V} < 1$) , that
one galaxy displays both high levels of star formation and dust obscuration
(${\rm SFR} \approx 300 M_\odot~{\rm yr}^{-1}$, $A_{\rm V} \approx 1.7$~mag),
and that the remaining galaxy has properties that are intermediate between the
quiescent and star-forming populations.
