Broadband submillimeter instrumentation for the detection of distant galaxies

I describe our efforts to search the universe for the faint far-infrared emission of galaxies as far away as possible. Details are given regarding the design, construction, use, and performance evaluation of the Submillimeter High Angular Resolution Camera (SHARC), a 24-element bolometer camera for imaging at 350$m$m and 450$m$m from the Caltech Submillimeter Observatory (CSO). This instrument has been used to observe the thermal dust emission from a sample of nearby galaxies and a sample of sources as distant as 90% of the way across the spacetime universe. The nearby sample is well-characterized by a single-component greybody dust emission model with a temperature of 37 $\pm$ 4K and a spectral emissivity index of $b$ = 1.7 $\pm$ 0.4. For the cosmologically distant sample, we find an average temperature of 53 $\pm$ 8K, a median luminosity of (2 $\pm$ 1) × 1013 $L\odot$ and a median dust mass of (3 $\pm$ 2) × 108 $M\odot$. This makes these objects some of the most massive and luminous ever observed, with an inferred star formation rate of 2000 $M\odot$ per year.; We have observed a sample of 0.02 $\le z\le$ 0.13 ultraluminous infrared galaxies in the J = 2 → 1 and J = 3 → 2 transitions of CO. We find that the 3 → 2 emission arises from an optically thick region with a temperature in the range 20 $\le T\le$ 60K and a molecular gas density of n(H₂) $\approx$ 1500 cm–3. At high redshifts (z > 2), however, most of our observations have resulted in nondetections. The emission in the NII 205$m$m line from the Cloverleaf quasar is found to be below the amount predicted locally, while for two z > 4 quasars, our upper limits to the CII 158$m$m line emission show a line luminosity ten times smaller than has been observed locally.; Finally, I detail our effort to develop a novel submillimeter spectrometer using a linear bolometer array as a detector element and relying on Fabry-Perot or immersed grating optics to provide the spectral dispersion. This approach promises to provide bandwidths several times larger than are available with existing heterodyne spectrometers, making the detection of cosmologically distant galaxies in their submillimeter line emission a reality.