  We have recently commissioned a novel infrared ($0.9-1.7$ $\mu$m) integral
field spectrograph (IFS) called the Wide Integral Field Infrared Spectrograph
(WIFIS). WIFIS is a unique instrument that offers a very large field-of-view
(50$^{\prime\prime}$ x 20$^{\prime\prime}$) on the 2.3-meter Bok telescope at
Kitt Peak, USA for seeing-limited observations at moderate spectral resolving
power. The measured spatial sampling scale is $\sim1\times1^{\prime\prime}$ and
its spectral resolving power is $R\sim2,500$ and $3,000$ in the $zJ$
($0.9-1.35$ $\mu$m) and $H_{short}$ ($1.5-1.7$ $\mu$m) modes, respectively.
WIFIS's corresponding etendue is larger than existing near-infrared (NIR)
IFSes, which are mostly designed to work with adaptive optics systems and
therefore have very narrow fields. For this reason, this instrument is
specifically suited for studying very extended objects in the near-infrared
such as supernovae remnants, galactic star forming regions, and nearby
galaxies, which are not easily accessible by other NIR IFSes. This enables
scientific programs that were not originally possible, such as detailed surveys
of a large number of nearby galaxies or a full accounting of nucleosynthetic
yields of Milky Way supernova remnants. WIFIS is also designed to be easily
adaptable to be used with larger telescopes. In this paper, we report on the
overall performance characteristics of the instrument, which were measured
during our commissioning runs in the second half of 2017. We present
measurements of spectral resolving power, image quality, instrumental
background, and overall efficiency and sensitivity of WIFIS and compare them
with our design expectations. Finally, we present a few example observations
that demonstrate WIFIS's full capability to carry out infrared imaging
spectroscopy of extended objects, which is enabled by our custom data reduction
pipeline.
