Annu. Rev. Astron. Astrophys. 1999. 37: 127-189
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6.3. Morphology of Highly Magnified Galaxies

Although the coupling of gravitational telescopes with the high resolution images from HST is superb for probing the intrinsic morphology of arc(let)s, no significant results have been raised from recent studies. Many HST images of arcs are made of two parallel elongated arcs, as in A2390 (Kneib et al, in preparation) or in MS2137-23 (Hammer et al 1997; see arcs A and C in MS2137-23 in Figure 3), which supports the idea that these distant galaxies are interacting systems, as it was reported in the previous section. Other images show bright spots which are interpreted as star forming regions, like Cl2244-02 (Hammer & Rigaud 1989), A2390 (Pelló et al, in preparation) or Cl0024+1654 (Colley et al 1996). In the case of the giant arc in Cl1358+62 at z = 4.92, the comparion of the visible and the near-infrared observations obtained with the HST and the Keck telescopes (Soifer et al 1998) reveals that one of its bright spots already contains half the stellar mass of the galaxy. It shows that at this redshift, galaxies may already have dense cores. Furthermore, the visible and near infrared imaging and spectrospic data show also that reddening produced by dust is important, even at that redshift.

The detailed description of a z approx 5-galaxy given by Soifer et al strengthens the usefulness of image reconstruction techniques of high-redshift lensed galaxies, as the one initially proposed by Kochanek et al (1989). Some attempts have already been made in Cl0024+1654 (Wallington et al 1995, Colley et al 1996) or in MS2137-23 (Hammer et al 1997). They succeed in reproducing a single image in the source plane, but the details of the morphology are still uncertain and do not yet provide valuable information on distant galaxies. Therefore, it is still premature to present quantitative results on the distant galaxies, first because this sample is poor and incomplete, and second because there are too many uncertainties in the source reconstruction.

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