The Initial Mass Function in the Nearest Strong Lenses from SNELLS:
  Assessing the Consistency of Lensing, Dynamical, and Spectroscopic
  Constraints
  We present new observations of the three nearest early-type galaxy (ETG)
strong lenses discovered in the SINFONI Nearby Elliptical Lens Locator Survey
(SNELLS). Based on their lensing masses, these ETGs were inferred to have a
stellar initial mass function (IMF) consistent with that of the Milky Way, not
the bottom-heavy IMF that has been reported as typical for high-$\sigma$ ETGs
based on lensing, dynamical, and stellar population synthesis techniques. We
use these unique systems to test the consistency of IMF estimates derived from
different methods. We first estimate the stellar $M_*/L$ using lensing and
stellar dynamics. We then fit high-quality optical spectra of the lenses using
an updated version of the stellar population synthesis models developed by
Conroy & van Dokkum. When examined individually, we find good agreement among
these methods for one galaxy. The other two galaxies show 2-3$\sigma$ tension
with lensing estimates, depending on the dark matter contribution, when
considering IMFs that extend to 0.08 Msol. Allowing a variable low-mass cutoff
or a nonparametric form of the IMF reduces the tension among the IMF estimates
to $<2\sigma$. There is moderate evidence for a reduced number of low-mass
stars in the SNELLS spectra, but no such evidence in a composite spectrum of
matched-$\sigma$ ETGs drawn from the SDSS. Such variation in the form of the
IMF at low stellar masses (m <~ 0.03 Msol), if present, could reconcile
lensing/dynamical and spectroscopic IMF estimates for the SNELLS lenses and
account for their lighter $M_*/L$ relative to the mean matched-$\sigma$ ETG. We
provide the spectra used in this study to facilitate future comparisons.
