Science Nugget—The TMT "First-Light" Instruments
  Paul Hickson
  University of British Columbia
  Interim Chair, TMT Science Advisory Committee (SAC)

In mid-December, two dozen scientists and engineers from across the U.S., Canada and Japan converged on Vancouver for a special three-day meeting of the TMT Scientific Advisory Committee (SAC). Despite hurricane-force winds that disrupted flights, damaged buildings, and left a quarter of a million people in the dark, the meeting went on. Under discussion was the scientific scope and vision of the TMT project.

Two years earlier, the SAC had laid out an ambitious plan for eight instruments and four adaptive optics systems that would enable the TMT to achieve its full potential. Now, with the benefit of many months of detailed engineering analysis and cost estimating by the project team, and several reviews by panels of independent experts, a choice had to be made. What would be the most effective set of "first-light" instruments—those available when the telescope first comes on line—that could fit within the construction budget?

The SAC weighed the scientific capabilities of the various instruments, and considered which would best provide synergy with other major new facilities such as the James Webb Space Telescope and the Atacama Large Millimeter Array. Our ambition was tempered by a finite cost cap. Indeed, one option was to reexamine the size of the telescope! Decreasing the primary mirror diameter from 30 to 25 meters would save money that could be used to build additional first-light instruments.

We debated the pros and cons of such a change and in the end, based upon the science, we decided against it. A key technology that gives the TMT much of its power is adaptive optics. Not only does adaptive optics provide unprecedented angular resolution (6 milliarcseconds at a wavelength of 1 micron), it also gives a tremendous boost in sensitivity. For a large and important class of scientific programs—the study of faint unresolved objects with adaptive optics—the sensitivity of a telescope is proportional to the fourth power of its diameter. Thus, a 30-meter telescope will be twice as sensitive as a 25-meter telescope.

We identified a suite of three first-light instruments that would provide a comprehensive and balanced scientific capability for the Thirty Meter Telescope. These three are an infrared imaging spectrometer (IRIS), an infrared multi-slit spectrometer (IRMS), and a wide-field optical spectrometer (WFOS).

Using the NFIRAOS multi-conjugate adaptive optic system, IRIS and IRMS together provide imaging, integral field and multi-slit spectroscopy at the diffraction limit. This will enable comprehensive studies of the faintest and most distant objects. Complementing this capability, WFOS will allow optical spectra to be obtained for hundreds of objects simultaneously.

This exciting set of first-light instruments will ensure that the TMT will do frontier science right from the start, and provide an effective complement to other ground- and space-based facilities.