Large telescopes in the 8- to 10-meter class have revolutionized the world of optical and near-infrared astronomy. Newly developed adaptive optics systems, which remove image distortions caused by the atmosphere, have made them even more powerful. Astronomers are poised to take the next major step—adaptive optics telescopes with 3 times the diameter, 10 times the optical collecting area, and up to 80 times the near-infrared sensitivity compared to existing telescopes. These Giant Segmented Mirror Telescopes (GSMTs) will be essential to understanding the distant galaxies discovered by JWST and to obtaining spectra of the faint transients found by LSST, and they will be transformative for a broad range of science aimed at understanding targets ranging from stars and exoplanets to black holes. Although they will function as observatories, they are integral parts of each of the survey’s target science areas as explained in Chapters 1 and 2. Operating in the optical and infrared (at 0.3 to 2.5 microns), the GSMTs excel at high-spectral- and high-spatial-resolution spectroscopy and will have a relationship to JWST similar to that of the 8- to 10-meter-class telescopes to HST.22
With every enormous leap in sensitivity come new discoveries we cannot anticipate, but the broad impact the GSMTs will have on the survey’s identified science questions is clear. The very first galaxies in the universe that will be found by JWST will require GSMTs for follow-up so as to determine their internal dynamical properties by studying the bulk motions of stars in a way that complements the gas observations of ALMA. GSMTs would also monitor how the chemical elements are built up. Their superb spatial resolution and astrometric capabilities would enable them to follow the orbits of individual stars around the several-million-solar-mass black hole in the center of our Milky Way galaxy so as to obtain precision measurements of fundamental galactic parameters. Direct imaging of exoplanet systems using the advanced adaptive optics cameras on these telescopes would also be an exciting area of study, given that GSMTs will have the highest angular resolution in the visible through infrared of any existing or planned facility, ground or space. They would also be able to study the reflected infrared emission of planets in the habitable zone. The ability of a GSMT to perform direct spectroscopy on very faint galaxies would be crucial in efforts to elucidate the properties of dark matter and merging black holes. These telescopes would transform understanding of stellar astronomy by taking high-dispersion spectra of local stars, mapping the flow of gas into and out of massive galaxies during their formative stage, and studying the formation of protoplanetary systems.