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

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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 [FORMULA]. Of the 11 objects listed in Table 1, seven had preliminary redshifts [FORMULA], placing them near or behind the absorption seen between [FORMULA] toward Q0122-380.

Of these seven high redshift candidates, only three (Q0117-380, Q0120-3781 and 0125-376) are confirmed as [FORMULA] 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 [FORMULA]. The four quasar candidates with lower preliminary redshifts [FORMULA] are all confirmed as such.

As is evident from Fig. 1, our low resolution spectra of two of the three confirmed [FORMULA] 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 [FORMULA] toward Q0122-380. However, the line detection limit of our spectra is only [FORMULA] Å at these wavelengths.

A more promising case is that of the final object, Q0125-376, whose redshift of [FORMULA] lies close to that of the absorption complex at [FORMULA] 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 ([FORMULA] Å) absorption features at [FORMULA] Å, [FORMULA] Å and [FORMULA] Å, respectively. The former two features are almost certainly due to C IV absorption from two [FORMULA] systems at [FORMULA] and [FORMULA], 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 [FORMULA].

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

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© European Southern Observatory (ESO) 2000

Online publication: July 7, 2000
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