Until recently, the CFHT was the crown jewel of the Canadian ground-based optical/near-IR program. While the Gemini telescopes are now the premier Canadian optical/NIR facilities, the CFHT continues to see active use, and this is largely due to the superlative site characteristics. During the coming decade new Canadian facilities are expected to come on line (e.g. the TMT, SKA), and it is anticipated that the Canadian community will want the CFHT to be in a position to complement these facilities (e.g. placing narrow field observations of faint sources obtained with the TMT or SKA in a wider field context, or providing spectroscopic follow-up of new imaging surveys). There is also the prospect of increased time exchange between facilities – if CFHT is to benefit from such opportunities then it should be positioned to offer capabilities that users who are not part of the CFHT consortium will want to access. This will in turn give Canadians access to facilities that they might not otherwise be able to use.
The GAC recommends the following guidelines for the future of the CFHT.
1) Exploit the CFHT site
The strengths of the current facility and the site must be recognized for continued use by future generations of Canadian astronomers. The paramount characteristic of the site is its excellent image quality. Exploiting the seeing of the CFHT site has proven to be of great benefit to the Canadian community, and will undoubtedly continue to be of interest in decades to come. The good IQ of the CFHT also provides a niche that will be beneficial to the CFHT when supporting other Canadian OIR facilities AND makes the CFHT valuable for time exchanges. Given that facilties like the TMT, SKA, and ALMA will observe sources that are much fainter than have heretofore been possible to study, it will be desirable to increase the light gathering power of the CFHT to allow it to probe fainter sources than is now possible.
The GAC thus recommends that any strategy for improving, upgrading, or re-instrumenting the CFHT continues to place emphasis on exploiting the good natural image quality – proposals in which the facility is relegated to a `light bucket’ should not be considered. From the context of providing long-term support for other Canadian facilities, it is recommended that the CFHT be upgraded to enhance its light-gathering power, while also maintaining a wide field of view.
2) Deploy instrumentation that is of interest to the broad Canadian user community
As a national facility, the CFHT has tended to offer instruments that have broad, work horse capabilties. A recent study by Dennis Crabtree has shown that of the three instruments currently on the CFHT (MegaCam, WIRCam, and EspaDons), MegaCam has produced 4 — 5 times more papers than the other two instruments combined. This shows the broad appeal of wide-field science at visible wavelengths to the Canadian community.
The GAC recommends that the CFHT instrument complement should maintain capabilities that are attractive to the Canadian community in general. Past experience suggests that this is best accomplished by instruments that offer work horse capabilties at visible wavelengths. In addition, work horse instruments also tend to have the highest degree of complementarity with other facilities in the Canadian ground-based and space-based facility suite – the prime example is GMOS on Gemini.
This does not mean that instruments that are geared for a specific program should be avoided entirely. It is recognized that some program-specific instruments may have broad applications to the community in general. In addition, there may be operational models where there are multiple instruments available, and a model in which some of these have work horse capabilties would also be acceptable. The GAC recommends that the CFHT not be configured in such a way that a niche instrument, that is of interest to only a small fraction of the community, is the only capability available.
3) Continue to offer PI access:
More and more time on 4 metre facilities is being dedicated to surveys, and the CFHT has been no exception. Still, there is continued pressure to continue PI science programs, which involve time requests that span a few nights, to those that extend over many semesters. PI and survey programs each have metrics that indicate that they are of interest to the user community. Dennis Crabtree has shown that PI driven programs produce more papers than those that result from surveys. However, surveys produce higher impact papers. Given this dichotomy in success metrics, the GAC recommends that the CFHT maintain a mix of PI and survey programs, notionally at the current level. A change in this recommendation could be spurred by a drop in subscription rates for PI programs.
4) Consult with the Canadian user community, and provide realistic projections for project success and timing.
The age of CFHT is such that to remain scientifically competitive, the facility needs to be upgraded and to provide some kind of dedicated/unique capability. It is the view of the GAC that new instrumentation should not take priority over the pressing need for a major upgrade of the telescope as a whole. Major upgrades will require that the facility be closed for an extended period of time. It is therefore important that the Canadian community be allowed to evaluate the expected payout that would be delivered at the end of any major upgrade.
In order to maintain flexibility in a rapidly changing astronomical landscape, the GAC recommnds that the CFHT should at present also avoid making other commitments that may tie up the site for up to a decade (e.g. very long-term surveys). Changes should also be avoided that may potentially (1) affect the ability to support other Canadian facilities, (2) affect the attractiveness of the facility for time exchanges, and (3) discourage potential new CFHT partners in an upgraded facility.