The wide integral field infrared spectrograph: commissioning results and on-sky performance

Abstract

We have recently commissioned a novel infrared (0.9 − 1.7 µm) 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 x 20 ) 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 ∼ 1 × 1 and its spectral resolving power is R ∼ 2, 500 and 3, 000 in the zJ (0.9 − 1.35 µm) and H short (1.5 − 1.7 µm) 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.Young supernova remnants (SNRs) are rich in NIR lines, which serve as diagnostics of supernova nucleosynthetic processes and explosions. This is especially true for the zJ-band that has transitions of iron, sulphur, phosphorus, oxygen, carbon, and helium, which have crucial information for the supernova nucleosynthesis and explosion mechanisms. WIFIS observations will make it possible to conduct precise abundance comparisons of the supernova nucleosynthetic elements. For instance, we have recently discovered an increased abundance of phosphorus in Casseopia A, 11 confirming the in-situ creation of phosphorus -one of the six indispensable elements of human * The principal investigator of WIFIS is Dae-Sik Moon.