We have discovered a new gravitational lens in the Cosmic Lens All-Sky Survey ( CLASS ) .
The lens B2045+265 is a four-image system with a maximum separation of 1 \farcs 9 .
A fifth radio component is detected , but its radio spectrum and its positional coincidence with infrared emission from the lensing galaxy strongly suggests that it is the radio core of the lensing galaxy .
This implies that the B2045+265 lens system consists of a flat-spectrum radio source being lensed by another flat-spectrum radio source .
Infrared images taken with the Hubble Space Telescope and the Keck I Telescope detect the lensed images of the background source and the lensing galaxy .
The lensed images have relative positions and flux densities that are consistent with those seen at radio wavelengths .
The lensing galaxy has magnitudes of J = 19.2 ^ { m } , m _ { F 160 W } = 18.8 ^ { m } and K = 17.6 ^ { m } in a 1 \farcs 9 diameter aperture , which corresponds to the size of the Einstein ring of the lens .
Spectra of the system taken with the Keck I Telescope reveal a lens redshift of z _ { \ell } = 0.8673 and a source redshift of z _ { s } = 1.28 .
The lens spectrum is typical of a Sa galaxy .
The image splitting and system redshifts imply that the projected mass inside the Einstein radius of the lensing galaxy is M _ { E } = 4.7 \times 10 ^ { 11 } h ^ { -1 } M _ { \sun } .
An estimate of the light emitted inside the Einstein radius from the K magnitude gives a mass-to-light ratio in the rest frame B band of ( M / L _ { B } ) _ { E } = 20 h ( M / L _ { B } ) _ { \sun } .
Both the mass and mass-to-light ratio are higher than what is seen in nearby Sa galaxies .
In fact , the implied rotation velocity for the lensing galaxy is two to three times higher than what is seen in nearby spirals .
The large projected mass inside the Einstein ring radius may be the result of a significant amount of dark matter in the system , perhaps from a compact group of galaxies associated with the primary lensing galaxy ; however , it may also arise from a misidentification of the source redshift .
A simple model of the gravitational potential of the lens reproduces the image positions well , but further modeling is required to satisfy the constraints from the image flux density ratios .
With further observations and modeling , this lens may yield an estimate of H _ { 0 } .