Broadband submillimeter instrumentation for the detection of distant galaxies

Citation

Benford, Dominic James (1999) Broadband submillimeter instrumentation for the detection of distant galaxies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7eha-q373. https://resolver.caltech.edu/CaltechETD:etd-06092008-100026

Abstract

This research details my efforts to search the universe for the faint far-infrared emission of galaxies as far away as possible. I first describe the design, construction, use, and performance evaluation of the Submillimeter High Angular Resolution Camera (SHARC), a 24-element bolometer camera for imaging at 350 microns and 450 microns from the Caltech Submillimeter Observatory (CSO). This instrument achieves background-limited performance and has been available for use by the international community since 1996. In the following two chapters, I detail the astronomical results attained with this instrument when used to observe the thermal dust emission from a sample of nearby galaxies (chapter 3) and a sample of sources as distant as 90% of the way across the spacetime universe (chapter 4). The nearby sample is well-characterized by a single-component greybody dust emission model with a temperature of 37 +/- 4K and a spectral emissivity index of beta = 1.7 +/- 0.4. Our cosmologically distant sample provides the first systematic study of these objects at wavelengths probing near the emission peak at a rest-frame wavelength of approximately 80 microns. We find an average temperature of 53 +/- 8K and determine a median luminosity of (2 +/- 1)x10^13 L_sun and a median dust mass of (3 +/- 2)x10^8 M_sun. This makes these objects some of the most massive and luminous ever observed, with an inferred star formation rate of 2000 M_sun per year. To balance the continuum emission results described above, I have observed both local and high-redshift galaxies with the CSO facility heterodyne receivers in an effort to detect the emission lines of CO, Cii, and Nii. We have observed a sample of 22 nearby (0.02 < z < 0.13) ultraluminous infrared galaxies in the J = 2 to 1 and J = 3 to 2 transitions of CO. Using published 1 to 0 intensities, we find that the 3 to 2 emission most likely arises from an optically thick region, implying that future observations in the higher-J lines can be used to constrain the temperature of the molecular gas in these galaxies. We find a most likely temperature in the range 20 < T < 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, but not without merit. The emission in the Nii 205 micron line from the Cloverleaf quasar is found to be below the amount predicted for a galaxy similar to M82. For two z > 4 quasars, our upper limits to the Cii 158 micron line emission show that the ratio of the line luminosity to the total luminosity is less than 0.01%, ten times smaller than has been observed locally. Finally, I shall detail our effort to design 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.

Thesis Files