Next Contents Previous

8. QSO ABSORPTION LINES AND LARGE-SCALE STRUCTURE

In March 1986, Steidel and I obtained spectra (~ 2 Å resolution, S/N ratio ~ 40) at the Las Campanas Observatory of two QSOs, Tol1037-2704 (zem = 2.193) and Tol1038-2712 (zem = 2.331), to which attention had been drawn by Jakobsen et al. (1986). The QSOs are separated by 17.9 arcmin on the sky. Confirming and extending the work of Jakobsen et al., it was found that there are at least five absorption systems in the spectrum of each QSO, occupying the same narrow range in redshift from 1.89 to 2.14. There is a statistically significant excess of absorption systems in the spectra of both QSOs; however, the tendency which was pointed out by Jakobsen et al. for the systems in one QSO to match a corresponding system in the other to within 1800 km s-1 was judged not to be significant (Sargent and Steidel 1987). For a Universe with q0 = 0.5, the separation of the two lines of sight is ~ 4.3 h100 Mpc, by far the largest distance over which correlated absorption has ever been seen. In addition, we obtained low-resolution (~ 4 Å) spectra of a fainter QSO Tol1038-2707 (only 5 arcmin from Tol1038-2712) which has a strong absorption system (zabs approx 1.887) which corresponds to one of the common absorption systems in the other two QSO spectra, as well as a spectrum of Tol1037-2742 containing a possible strong absorption system at z ~ 1.86. In April 1987, another nearby QSO, Tol1035-2737, was found to have a redshift of zem = 2.168 and to have absorption redshifts at zabs = 2.125, 2.040 and 1.905, respectively. Collectively, these observations suggest that this general direction in the sky contains a large supercluster extending from a redshift of around z = 2.14 to 1.86. Tol1038-2712 lies behind the supercluster, Tol1037-2704 and Tol1035-2737 lie at its most distant edge, while Tol1038-2707 is close to the nearer edge. The supercluster has an extent along the line of sight of ~ 50 Mpc at the epoch corresponding to z ~ 2. Its boundaries on the plane of the sky are not known as yet; however, the extent in this direction is at least 10 Mpc. Such extended structures, if elongated, would produce a non-Poissonian distribution of number of absorption redshifts per QSO of the kind referred to in the discussion of the results of the CIV survey.