Large format imaging spectrograph for the Large Submillimeter Telescope (LST)

We present a conceptual study of a large format imaging spectrograph for next-generation large (50-m class) single-dish telescopes, i.e., the Large Submillimeter Telescope (LST) and Atacama Large Aperture Submillimeter Telescope (AtLAST). Recent discoveries of high-redshift star-forming galaxies at z=8-9 and candidate quiescent galaxies at z~6 indicate the onset of earliest star formation just a few 100 million years after the Big Bang (i.e., z = 12 - 15), and LST/AtLAST will provide a unique pathway to uncover spectroscopically-identified ``first forming galaxies'' in the pre-reionization era, once it will be equipped with a large format imaging spectrograph. We describe the preliminary of 3-band, medium resolution (R=2000) imaging spectrograph with ~1.5 M detectors in total based on the KATANA concept (Karatsu et al.~2019), which exploits technologies of the integrated superconducting spectrometer (ISS) and a large-format imaging array like A-MKID.