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


Fassnacht, Christopher D. (1999) Determining the distance scale with CLASS: studies of two new gravitational lenses and a measurement of the Hubble constant. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/pe8p-yc41.


NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

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 H[...]. A measurement of H[...] requires the redshifts of the lensing object and the background source, a well-constrained model of the gravitational potential of the lensing object, and a measurement of time delays between the images of the background source.

The 1608+656 system contains four images of the background source, which is the unresolved core of a classical radio double source. The lensing galaxy is at a redshift of [...] = 0.630, while the background source is at a redshift of [...] = 1.394. Interestingly, the spectrum of the background object indicates that it is an "E + A" galaxy. Ground-based optical and infrared images clearly show the lensing galaxy at the location predicted by the lens models. Images taken with instruments on 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 [...] = 0.8673. The spectrum of the background source shows one broad emission line, which appears to be Mg II at a redshift of [...] = 1.28. However, this redshift implies that the lensing galaxy is unusually massive and would have a rotation velocity two to three times what is observed in nearby galaxies of the same type. There is either a significant contribution by dark (or underluminous) matter associated with the lensing object or the source redshift is incorrect. More sensitive spectroscopy is needed to resolve this issue.

Preliminary observations of the 1608+656 system showed that the component flux densities varied by ~15% on time scales of months. For this reason, I conducted a dedicated monitoring program with the Very Large Array (VLA) 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. Although the fractional variations are small, the time delays between the curves can be measured. The final values are [...], and [...], where the 95% confidence levels have been obtained from Monte Carlo simulations. 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 H[...] from a CLASS lens: H[...] = [...] (statistical) ± 15(systematic) km sec[superscript -1] Mpc[superscript -1].

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Readhead, Anthony C. S.
Group:Astronomy Department
Thesis Committee:
  • Unknown, Unknown
Defense Date:19 October 1998
Record Number:CaltechETD:etd-09232008-094506
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3735
Deposited By: Imported from ETD-db
Deposited On:24 Oct 2008
Last Modified:16 Apr 2021 23:07

Thesis Files

PDF (Fassnacht_cd_1999.pdf) - Final Version
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