ACWI: an experiment to image the Cosmic Web from Antarctica

Abstract

The Antarctic Cosmic Web Imager (ACWI) is a dedicated 2m-class telescope specifically designed to discover and map resonance UV line emission from the Intergalactic Medium (IGM) and to explore the low surface brightness universe. IGM mapping will provide a new measurement of large-scale structure and the distribution of dark matter over a large and unique range in overdensity. The South Pole provides a location with (1) a target elevation that is constant during observation hence sees constant airmass (2) the lowest measured extinction of any ground based site (3) a low and constant ecliptic elevation and hence zodiacal emission away from the target location and (4) long duration nights yielding stable sky and instrument properties enabling the required accurate sky subtraction. These factors combined imply a sky background that is the most stable of any ground-based site, a requirement for this particular science case where the subtraction of sky background, rather than the image quality, must be exquisite. We present the baseline instrument design that is catered to perform this science case only and is not a general purpose instrument, increasing robustness and reliability.