Computer Science – Performance
Scientific paper
Sep 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt.........9w&link_type=abstract
Thesis (PhD). CALIFORNIA INSTITUTE OF TECHNOLOGY, Source DAI-B 63/03, p. 1397, Sep 2002, 171 pages.
Computer Science
Performance
1
Scientific paper
A 690 GHz heterodyne receiver was developed to observe the J = 6 → 5 rotational emission line of carbon monoxide (CO) in extragalactic sources. This receiver is based on a niobium superconductor-insulator- superconductor (SIS) mixer with a twin-slot antenna in a superconducting NbTiN ground plane. A 4 8 GHz low- noise amplifier was developed to amplify the intermediate frequency signal from the mixer with a spectral bandwidth of 1,700 km/s, enough to observe the broadest extragalactic submillimeter emission lines with a single receiver tuning. This amplifier is a quasi-monolithic microwave integrated circuit (QMMIC); three InP high- electron-mobility transistors (HEMTs) were bump-bonded to a passive thin-film GaAs circuit. The measured amplifier gain is 32 dB and the noise is approximately 8 Kelvin from 4 to 8 GHz at a physical temperature of 4 Kelvin. The receiver double-sideband noise temperature is 180 Kelvin. Prior to this development effort, a versatile microwave simulation package was written to calculate and optimize the signal and noise performance of high-frequency circuits, especially those containing superconductors and superconducting tunnel junctions. Using this package, called SuperMix, C++ programs can be written to simulate and optimize circuits of arbitrary size, complexity, and topology. SuperMix was used to simulate the complete 690 GHz SIS receiver. The receiver was used at the Caltech Submillimeter Observatory to map 12CO J = 6 → 5 emission in the central kiloparsec of the starburst galaxy M82 at a resolution of 14 arc seconds. Hot spots were found on either side of the dynamical center. The 12CO J = 6 → 5 map, along with measurements of nine other CO lines, were analyzed in the context of a two-component large velocity gradient (LVG) excitation model. Likelihood curves were calculated for the model parameters and related physical quantities based on the measured line intensities and their associated uncertainties to reveal how well various quantities can be constrained by the CO observations. The results of this analysis suggest that the warm gas is less dense than the cool gas, and that over half of the total molecular gas mass in these nuclear regions is warmer than 50 K.
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