Determining the distance scale with CLASS: Studies of two new gravitational lenses and a measurement of the Hubble Constant

Details Determining the distance scale with CLASS: Studies of two new gravitational lenses and a measurement of the Hubble Constant Determining the distance scale with CLASS: Studies of two new gravitational lenses and a measurement of the Hubble Constant

Jul 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........1f&link_type=abstract

Thesis (PhD). CALIFORNIA INSTITUTE OF TECHNOLOGY, Source DAI-B 60/01, p. 219, Jul 1999, 199 pages.

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Gravitational lenses have the potential to be excellent tools for investigating the Universe. This thesis describes the Cosmic Lens All-Sky Survey (CLASS), a program to find new gravitational lenses, and presents data on two newly-discovered lenses, 1608+656 and 2045+265. One of the major goals of CLASS is to find ``golden lenses,'' which can be used to measure the Hubble Constant (H0). The 1608+656 system contains four images of the background source. The lensing galaxy is at a redshift of zl = 0.630, while the background source is at zs = 1.394. Ground-based optical and infrared images clearly show the lensing galaxy. Images taken with the Hubble Space Telescope further resolve the lensing galaxy into two distinct objects, which may be a merging pair of galaxies. Radio maps of the 2045+265 system also show four images of the background source. In addition, a fifth component appears in the maps. The radio spectrum of the fifth component is significantly different from the spectra of the other four components, and its location matches that of the lensing galaxy to within the positional errors. Therefore, it appears that the fifth component is the flat-spectrum core of the lensing galaxy. The redshift of the lensing galaxy is zl = 0.8673. The redshift of the background source is z s = 1.28, based on one broad emission line. I conducted a dedicated monitoring program on 1608+656 with the Very Large Array from October 1996 to May 1997. The observations took place, on average, every four days. The calibrated light curves for components A, B, C, and D show variations in flux density at the 3-5% level. The time delays between the light curves are DtBA=30+5-7 d,DtBC=36+5 -8d, and DtBD=76+6-7 d. The model of the mass distribution of the lens correctly reproduces the image positions, flux ratios, and time delay ratios. The combination of the measured time delays with the lens model yields the first determination of H0 from a CLASS lens: H0 = 59+5-4 (statistical) +/- 15(systematic) km sec-1 Mpc-1.

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