The Cosmic Web Imager is a slicer based integral field spectrograph built for the Cassegrain focus of the 200" Hale Telescope at the Palomar Observatory. It is designed to detect faint emission from extended regions, especially the Intergalactic and Circumgalactic Media with redshifts 1.5 < z < 4. Twenty-four 1 mm x 16 mm slicer mirrors yield a 60"x40" field of view. A suite of Volume Phase Holographic gratings give a resolution R~5000 and make accessible a total wavelength range from 370nm to 950nm, with instantaneous bandwidth of around 14 nm when the nod-and-shuffle technique is employed, and ~45 nm otherwise. The instrument uses the legacy Norris Spectrograph lens and the blue-enhanced E2V CCD 231-84 as its detector. The overall system throughput is 20% with a peak toward the blue edge of the wavelength range. The nominal mode of operation uses the nod-and-shuffle technique which allows for more accurate background subtraction. The instrument was commissioned in July 2009 with subsequent observation runs in November 2009, March and May 2010.
CWI layout on optical bench.
Simulation of cosmic web emission with CWI field of view.