GMT Integral-Field Spectrograph (GMTIFS) conceptual design

The Giant Magellan Telescope (GMT) Integral-Field Spectrograph (GMTIFS)(c) is one of six potential first-light instruments for the 25m-diameter Giant Magellan Telescope. The Australian National University has completed a Conceptual Design Study for GMTIFS. The science cases for GMTIFS are summarized, and the instrument capabilities and design challenges are described. GMTIFS will be the work-horse adaptive-optics instrument for GMT. It contains an integral-field spectrograph (IFS) and Imager accessing the science field, and an On-Instrument Wave-Front Sensor (OIWFS) that patrols the 90 arcsec radius guide field. GMTIFS will address a wide range of science from epoch of reionization studies to forming galaxies at high redshifts and star and planet formation in our Galaxy. It will fully exploit the Laser Tomography Adaptive Optics (LTAO) system on the telescope. The tight image quality and positioning stability requirements that this imposes drive the design complexity. Some cryogenic mechanisms in the IFS must set to similar to 1 mu m precision. The Beam-Steering mechanism in the OIWFS must set to milli-arcsecond precision over the guide field, corresponding to similar to 1 mu m precision in the f/8 focal plane. Differential atmospheric dispersion must also be corrected to milli-arcsecond precision. Conceptual design solutions addressing these and other issues are presented and discussed.