Astron. Astrophys. 359, 429-432 (2000)

3. Discussion

Romani et al. (1991) originally drew attention to the rich absorption line quasar Q0122-380 on the basis that it was surrounded by a number of quasar candidates closer than . Of the 11 objects listed in Table 1, seven had preliminary redshifts , placing them near or behind the absorption seen between toward Q0122-380.

Of these seven high redshift candidates, only three (Q0117-380, Q0120-3781 and 0125-376) are confirmed as quasars. Of the remainder, one (0117-378) could not be located, two (0121-379 and 0123-372) are identified as stars, and another (Q0120-3785) turns out to be at a lower redshift of . The four quasar candidates with lower preliminary redshifts are all confirmed as such.

As is evident from Fig. 1, our low resolution spectra of two of the three confirmed quasars (Q0120-3781 and Q0117-380) reveal no obvious C IV absorption features in the wavelength range 4350-4600 Å that could potentially be associated with the absorption spanning toward Q0122-380. However, the line detection limit of our spectra is only  Å at these wavelengths.

A more promising case is that of the final object, Q0125-376, whose redshift of lies close to that of the absorption complex at in Q0122-380. Moreover, our spectrum of Q0125-376 (which has a better S/N ratio than those of Q0120-3781 and Q0117-380) shows three strong ( Å) absorption features at  Å,  Å and  Å, respectively. The former two features are almost certainly due to C IV absorption from two systems at and , an interpretation that is further strengthened by plausible detections of matching Si IV lines at shorter wavelengths. Based on a matching weaker feature seen at the anticipated position of Al III , we tentatively identify the third feature as the C IV trough of a weak and possibly detached BAL-like complex at .

The two systems seen in Q0125-376 could conceivably be associated with the absorption seen toward Q0122-380, falling squarely between the complex and the weaker system detected in that object by Carswell et al. (1982). In a standard cosmological model with the angular distance between Q0125-376 and Q0122-380 of at , corresponds to a projected comoving separation of Mpc , which is comparable to the extent of local superclusters of galaxies.

On the other hand, the presence of possibly BAL-like absorption at lower redshift would argue that the two systems seen in Q0125-376 are intrinsic in nature.

While higher resolution observations would be required to further delineate these possibilities and properly map the absorption toward the three confirmed quasars above, the exploratory observations presented here already make it clear that the field surrounding Q0122-380 is not as promising for searching for large scale structure at high redshift as had initially been hoped.

© European Southern Observatory (ESO) 2000

Online publication: July 7, 2000
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