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NOAO Newsletter - Director's Office - June 2000 - Number 62


Planning the GSMT

Steve Strom

A decade from now, astronomers will have access to major new tools on the ground (ALMA) and in space (NGST). To exploit these tools fully will require a new generation optical/infrared telescope with angular resolution matched to ALMA, sensitivity sufficient to characterize the faintest sources imaged by NGST, and a combination of field of view and collecting area matched to efficient study of the first emerging large-scale structures in the distant universe--a major scientific driver for both ALMA and NGST.

The minimum-size facility capable of satisfying these requirements is an ~30-50 m diameter telescope, capable of delivering diffraction-limited images (Strehl ~ 0.5) at wavelengths 1 micron and longward during atmospheric conditions which enable adequate adaptive corrections (thereby providing 10 mas images matched to ALMA), with sensitivity to faint sources enabling R ~ 5000 spectroscopy at I(AB) ~27 mag (sufficient to obtain redshifts and global kinematics for z > 1 galaxies), and with a native-seeing field of view sized to enable efficient statistical studies of large-scale structure on spatial scales ~100 Mpc at z>1 via multiplexed spectroscopy of hundreds of background QSOs and thousands of galaxies simultaneously. In practice, this requires fields of projected linear size no smaller than 10 Mpc (at z > 1, this corresponds to ~20 arcmin for h ~ 100). A facility (which for the moment we call the 'Giant Segmented-Mirror Telescope,' or GSMT) providing this combination of sensitivity and angular resolution will not only be an essential complement to ALMA and NGST, but will also enable science qualitatively different from that of current generation ground- and space-based O/IR telescopes.

Owing to the central importance of developing GSMT before the end of the next decade, NOAO has established a New Initiatives Office (NIO), charged initially with developing viable design concepts for next generation telescopes--ranging from the 30-50 m GSMT to an 'ultimate' ground-based telescope of size ~ 100 m--before the end of 2002, and establishing the appropriate partnerships for completing a ~30-m telescope before 2012, in time to complement NGST and ALMA.

NIO resides within NOAO's new Planning and Development Office, has an initial core staff drawn from both NOAO and the International Gemini Project, and is guided by advice provided by a steering committee comprising senior representatives from NOAO, Gemini, the major US independent observatories, and from government laboratories and the DoD.


Caption: Academic and Private Sector Participants in GSMT Workshops.

It is recognized from the outset that design and development of GSMT represents a substantial effort whose ultimate success will depend on the combined efforts of the NIO, the US independent observatories, industry in the US, and possibly international partnersboth astronomical and industrial. Our underlying strategy is first to build a strong US technical position capitalizing on the combined capabilities of the national observatories and independent observatories, and second to engage potential partnersboth national and internationalin a constructive way that will achieve mutual aims. Over the past nine months, NIO staff working with the community have begun to identify key science drivers; critical enabling technologies; performance requirements; design options; technical issues and challenges, including those for a baseline instrument complement; essential design studies; and a process for identifying and evaluating potential sites for GSMT.

These efforts have been divided among eight task groups, which together have engaged the talents of scientists and engineers drawn from a broad cross section of the astronomical community and the private sector. Through the auspices of AURA, NIO has established close contacts with the California Extremely Large Telescope (CELT) and ESO Overwhelmingly Large Telescope (OWL) projects with the aim of coordinating efforts to achieve mutual goals rapidly and at lower combined cost. We plan to synthesize the efforts of the task groups by mid-May, and before mid-June to present NSF AST and MPS with a roadmap for a nationally based effort to explore the designs and technologies critical to developing a GSMT concept. The roadmap will also describe the mechanisms by which NOAO-NIO proposes to engage the talent and energies of the university community and private sector in carrying out enabling studies for GSMT.


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