The SINFONI Nearby Elliptical Lens Locator Survey: Discovery of two new
  low-redshift strong lenses and implications for the initial mass function in
  giant early-type galaxies
  We present results from a blind survey to identify strong gravitational
lenses among the population of low-redshift early-type galaxies. The SINFONI
Nearby Elliptical Lens Locator Survey (SNELLS) uses integral-field infrared
spectroscopy to search for lensed emission line sources behind massive lens
candidates at $z$<0.055. From 27 galaxies observed, we have recovered one
previously-known lens (ESO325-G004) at $z$=0.034, and discovered two new
systems, at $z$=0.031 and $z$=0.052. All three lens galaxies have high velocity
dispersions (\sigma>300 km/s) and \alpha-element abundances ([Mg/Fe]>0.3). From
the lensing configurations we derive total J-band mass-to-light ratios of
1.8$\pm$0.1, 2.1$\pm$0.1 and 1.9$\pm$0.2 within the $\sim$2 kpc Einstein
radius. Correcting for estimated dark-matter contributions, and comparing to
stellar population models with a Milky Way (Kroupa) initial mass function
(IMF), we determine the "mass excess factor", \alpha. Assuming the lens
galaxies have "old" stellar populations (10$\pm$1 Gyr), the average IMF mass
factor is $\langle\alpha\rangle$=1.10$\pm$0.08$\pm$0.10, where the first error
is random and the second is systematic. If we instead fit the stellar
populations from 6dF optical survey spectra, all three galaxies are consistent
with being old, but the age errors are 3-4 Gyr, due to limited signal-to-noise.
The IMF constraints are therefore looser in this case, with
$\langle\alpha\rangle$ = $1.23^{+0.16}_{-0.13}\pm{0.10}$. Our results are thus
consistent with a Kroupa IMF (\alpha=1.00) on average, and strongly reject very
heavy IMFs with \alpha>2. A Salpeter IMF (\alpha=1.55) is inconsistent at the
3.5$\sigma$ level if the galaxies are old, but cannot be excluded using age
constraints derived from the currently-available optical spectra.
