7.1. New technologies for instrumentation
A key technology under development is for bolometers with superconducting temperature-sensitive elements, including transition-edge sensors (TESs). These are much more stable than the semiconducting thermistors used in existing systems, and so can be read out using multiplexed, and therefore much simpler, cold electronics. Another advantage of TES devices is that they require no bias current, and so need fewer heat-conducting, difficult-to-assemble connections to each device. The prototype Fabry-Perot spectroscopic device FIBRE, which uses TES bolometers (Benford et al., 2000), was tested successfully at the CSO in May 2001.
TES devices offer the prospect of increasing the size of the arrays of detector elements in mm/submm-wave cameras from of order 100 to of order 104-5, providing much larger fields of view. Filled-array detector devices using conventional semiconducting bolometers are being demonstrated in the SHARC-II and HAWC cameras for the CSO and SOFIA, while the SCUBA-II camera has a goal of at least a 8 × 8 arcmin field of view - about 25 times greater than the field of view of SCUBA - is under development in Edinburgh and is expected to integrate large arrays and superconducting bolometers. SCUBA-II will supplement its much wider field of view with an enhanced point source sensitivity: the same galaxies should be detectable about 8 and 4 times faster using SCUBA-II as compared with SCUBA at wavelengths of 850 and 450 µm respectively: see Table 1. A 10-m telescope operating at 850-µm with a 105-element detector would have a square field of view about 1 deg on a side, at a Nyquist-sampled plate scale: much larger than the 5-arcmin2 fields of view of SCUBA and MAMBO. With such large fields of view, it is not unreasonable to survey most of the sky down to the confusion limit of a 10-30-m telescope in an observing campaign lasting for several years.
By combining large numbers of bolometer detectors with dispersive mm-wave optics (Glenn, 2001), it should be possible to obtain low-resolution mm-wave spectra of galaxies over a very wide band, perhaps 100 GHz, to search for CO and atomic fine-structure line emission from high-redshift submm galaxies detected in continuum surveys, while simultaneously carrying out unbiased surveys for line-emitting galaxies within the field of view (Blain et al., 2000b). Development of several such systems is underway.
Phase-sensitive heterodyne submm detectors are already very efficient; however, only small numbers of these detectors can currently be fabricated into an array. Their strength is in very high resolution submm-wave spectroscopy, and as sensitive coherent detectors in existing mm-wave interferometers. They will be fitted to the forthcoming SMA and CARMA, and will be be exploited to the full with the large collecting area of the ALMA array.
Sensitive arrays of mid- and far-IR detectors should soon be flying, both in space aboard SIRTF and ASTRO-F, and in the upper atmosphere, on balloons such as BLAST, and aboard SOFIA. Limits to the continuum flux densities of the most luminous high-redshift galaxies derived using these facilities, measured close to the peak of their SED (see Fig. 2), will provide valuable information about their properties. Spectrographs, both aboard these facilities and on ground-based telescopes, will provide detections of and sensitive limits to the line radiation from the same objects, providing redshift information and astrophysical diagnostics.