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and Cosmology

Extragalactic Astronomy and Cosmology: An Introduction

Extragalactic Astronomy and Cosmology: An Introduction

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6. Clusters <strong>and</strong> Groups of Galaxies<br />

268<br />

Fig. 6.39. The cluster of galaxies Cl0939+4713 (A851) is the<br />

cluster with the highest redshift in the Abell catalog. The<br />

HST image in the upper left panel was obtained shortly after<br />

the refurbishment of the HST in 1994; in this image, North<br />

is down, whereas it is up in the bottom images. The mass<br />

distribution of the cluster was reconstructed from this image<br />

<strong>and</strong> is shown in the upper right panel, both as the level surface<br />

<strong>and</strong> by the contours on top. We see that the distributions<br />

of bright galaxies <strong>and</strong> of (dark) matter are very similar: their<br />

respective centers are aligned, a secondary maximum exists in<br />

both the light <strong>and</strong> the matter distribution, as does the prominent<br />

minimum in which no bright galaxies are visible either. This<br />

cluster also shows strong lensing effects, which can be seen<br />

from the image at the bottom: a triple image system at z ≈ 3.98<br />

<strong>and</strong>anarcwithz = 3.98 were confirmed spectroscopically

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