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SWIFT - a short wavelength integral field spectrograph for large telescopes

Final Activity Report Summary - SWIFT (SWIFT - a short wavelength integral field spectrograph for large telescopes)

The SWIFT project has designed and built a new astronomical instrument to exploit a niche in current technologies. The instrument will be mounted on the historic 200-inch telescope at Mount Palomar in California and will take advantage of the adaptive optics facility available there. Over the next five years, SWIFT will be used to study a range of astronomical objects, from the earliest galaxies to local star formation regions.

The key feature of SWIFT is its ability to take a spectrum at each point across a two-dimensional field. This means that SWIFT unlike a conventional spectrograph which can only take spectra along a one-dimensional line, is ideally suited to the study of extended objects such as galaxies. SWIFT achieves this through an image-slicer; a complex optical assembly with 'slices' a rectangular field into many separate strips and rearranges end-to-end in a long line. The image slicer in SWIFT, currently the largest in any astronomical instrument, produces 44 slices each 89 pixels long. As such, SWIFT obtains a spectrum at each point in a 44x89 pixel field of view (3 916 spectra in total) covering 21 by 10.5 arcseconds.

The spectrograph in SWIFT is designed to work optimally between 650 and 1 050 nanometres; wavelengths just above what the human eye can detect. This region is of particular interest as it falls in a technology gap between the traditional optical (300-800 nm) and infra-red (1 000 nm+) regions of the spectrum. Traditional CCDs used in the optical have very low efficiency beyond 800 nm, and while infrared detectors are capable of observing this regime their quality and cost-per-size are many years behind CCDs. For SWIFT, we have employed a new development in CCD techonology (thick CCDs) which give very good efficiency right up to 1 000 nm. Using these devices allows SWIFT to work effectively in a wavelength region which has been very tricky for previous instruments. This region is ideally suited to studying the most distant galaxes (z~7), as well as galaxies in the poorly understood 'redshift desert' from z~1-2.

The third key technology employed by SWIFT is the adaptive optics facility at Mount Palomar. PALAO, as the system is known, corrects for the very rapid turbulent effects in the atmosphere ('seeing'), and delivers sharp images comparable to those taken from space. This will allow SWIFT to study objects in greater detail, and with greater sensitivity, than a normal 'seeing-limted' instrument. In addition, the PALAO system has recently been equipped with a laser guide star, which allows the system to generate an artificial reference star anywhere on the sky. This LGS frees the system from the requirement of having a bright star near the target, and lets it observe any target irrespective of location.

By combining three specialties of integral field spectroscopy, high angular resolution and red-sensitive CCDs, SWIFT has created a niche in current technology. This niche will allow it to address specific questions in astronomy several years before comparable instruments are available on other telescopes.

The instrument has been designed and built over four years by a small team at the University of Oxford Department of Physics. The instrument will be delivered to Mount Palomar observatory in August 2008. In return for providing the instrument, University of Oxford astronomers are guaranteed 120 nights of observing time at Palomar over the next five years. This will be an invaluable resource for the group, and will no doubt spawn many research ideas and post-doctoral projects. SWIFT has cemented the formation of an optical / near-infrared instrumentation group at Oxford. The experience gained through this project has already proved key to future funding.

An international consortium led by members of the SWIFT team has recently been awarded a contract to study a similar instrument for the European Extremely Large Telescope (E-ELT); the next major telescope to be built by the European astronomical community. This has secured the jobs of two members of the team in the immediate future, and will potentially lead to the creation of several more over the next decade.