CLASS B0218+357 and the Hubble Constant
T. York [1], N. Jackson [1], I.W.A. Browne [1],
O. Wucknitz [2], J. Skelton [1]
- University of Manchester, Jodrell Bank Observatory
- Institute of Physics, University of Potsdam
Abstract
We present deep optical observations of the gravitational lens system
CLASS B0218+357, from which we derive an estimate of the Hubble
constant. Extensive radio observations have reduced the degeneracies
between the Hubble constant and the mass model in this lens to one
involving only the position of the radio-quiet lensing galaxy relative
to the lensed images. B0218+357 has an image separation of only 334
mas, so optical observations have previously been unable to resolve
the lens galaxy from the bright lensed images. Using the new Advanced
Camera for Surveys installed on the Hubble Space Telescope, we have
measured the separation between the lens galaxy centre and the
brightest image. Consequently we find a value for the Hubble constant
of 73+/-8 km/s /Mpc (68% confidence). This estimate is consistent with
the local value obtained from the Hubble Key Project, and with the
value from WMAP.
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