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Science with the Thirty Meter Telescope: The Young and Distant Universe

Sometime during the first 300 million years after the Big Bang, the first tiny seeds of galaxies began to collapse and form stars. As these galaxies grew during the subsequent 300–400 million years they ionized the hydrogen gas that permeated the cosmos.

Although early galaxies played a key role in our own cosmic history, understanding them has remained a daunting challenge: they are extraordinarily faint and all of their light has been shifted by the expansion of the Universe to infrared wavelengths and beyond.

These challenges, however, have helped drive the design and early light instrumentation of the Thirty Meter Telescope (TMT), which will offer extraordinary new capabilities to study the early, distant Universe, including the first stars and galaxies.

Models of the formation of stars in the pristine gas of early times suggest that star formation was once dramatically different from the stellar births that happen in the local Universe. Because the Universe originally lacked metals (elements heavier than lithium) that cool collapsing gas clouds today, the earliest stars were more massive and burned much hotter than even the largest stars we study today. This so-called “Population III” star formation is widely sought as evidence that our theories of the early epochs of the formation of galaxies in the Universe are correct.

Currently, the best prospects for direct detection of Population III star formation may come from spectroscopy of extremely faint galaxies in the near-infrared, where TMT will be optimized for extremely detailed study. TMT also will complement the James Webb Space Telescope (JWST) in this area by bringing to bear extremely sensitive moderate-resolution spectroscopy to study their physical proportions and properties, as well as reveal their ages and compositions.

At first light, TMT—armed with the NFIRAOS adaptive optics facility and IRIS (Infrared Imaging Spectrometer)—may even detect some of the youngest and most pristine early galaxies through their faint Lyman alpha emission, which does not readily penetrate a neutral medium. With its highly sensitive IR capabilities, TMT will extend our studies of this important line emission, revealing the scale of clustering of early Lyman alpha galaxies and thereby helping to track the evolution of ionization through cosmic time.

In studying later cosmic epochs, at least 1.5 billion years after the Big Bang, TMT will be able to dissect galaxies during the peak epoch of galaxy and black hole formation. One of TMT’s first-light instruments, WFOS (see below) will also allow new understanding of the composition of the intergalactic medium that fills space, revealing how heavy elements were spread by early star formation.

Observations of these “middle-aged” galaxies will exploit both the light gathering power and the unique angular resolution provided by TMT.

The current generation of 8–10 meter telescopes continues to expand our understanding of the very early Universe, but many of the great mysteries and unanswered questions will remain until TMT opens its extraordinarily powerful eye and probes even deeper into the furthest reaches of our Universe.

First Light Instruments

Wide Field Optical Spectrometer (WFOS)
The Wide Field Optical Spectrometer (WFOS) will provide near-ultraviolet and optical (0.3–1.0 μm wavelength) imaging and spectroscopy over a more than 40 square arcminute field-of-view. Using precision cut focal plane masks, WFOS will enable long-slit observations of single objects as well as short-slit observations of hundreds of objects simultaneously. WFOS will use natural (uncorrected) seeing images.

Infrared Imaging Spectrometer (IRIS)
The Infrared Imaging Spectrometer (IRIS) will be mounted on the observatory Adaptive Optics system and be capable of diffraction-limited imaging and integral-field spectroscopy at near- infrared wavelengths (0.8–2.5 μm).

Infrared Multi-object Spectrometer (IRMS)
The Infrared Multi-object Spectrometer (IRMS) will allow close to diffraction-limited imaging and slit spectroscopy over a 2 arcminute diameter field-of-view at near-infrared wavelengths (0.8–2.5 μm).

By Elizabeth (Betsy) Barton, TMT Science Advisory Committee Member Project Scientist, InfraRed Imaging Spectograph (IRIS)

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