The identification of two z3.8 QSOs
in a deep CCD survey

Analysis and Discussion

We identify strong, broad emission-lines associated with Ly1216, Ly1026, SiIV1397 and CIV1549 in the spectra of both QSOs (Fig. 3). Observed wavelengths, equivalent widths and FWHM of the lines were measured interactively with the IRAF task SPLOT, these are all listed in Table 2.  From the SiIV and CIV lines we estimate the redshifts of the two QSO as and , for Q1332+5034 and Q1722+3211 respectively.

Table 2: Catalogue of Spectral Features.

6 Q1332+5034 ID

z

EW (Å)

FWHM (Å)

Comment Ly

Using the redshifts calculated above we estimate luminosities of for Q1332+5034 and for Q1722+3211. At these redshifts their modest apparent magnitudes, compared to other QSOs, means that these two sources are roughly an order of magnitude less luminous than the median luminosity of known QSOs. The observed X-ray flux of Q1322+5034 represents a luminosity of erg s in the 0.5-11.6 keV band.

The spectrum of Q1332+5034 shows a number of strong absorption features shortward of Lyman- emission in the QSO. These include at least three relatively strong features within 100Å (5000 km sec) of the peak of the Lyman- emission in the QSO. Similar `associated' absorbers are commonly seen in radio and X-ray bright QSOs. However, the more interesting absorbers are further to the blue, the first of these, DLA-1, is at 5398Å and we identify this as a damped Lyman- absorber at z=3.439. This system completely obscures the background QSO at wavelengths below 912Å in its rest-frame and also produces detectable CIV and Ly- absorption (Fig. 3).

Identifying the lower redshift absorption system in the spectrum of Q1332+5034 with Lyman- absorption gives its redshift as . This feature is extremely strong, with a rest-frame equivalent width of 35Å, and if formed from a single absorption system would indicate a column density of around -22.0. Some support for this identification comes from the tentative detection of FeII 2383 and FeII 2374 at the extreme red-end of our spectrum, although these coincide with strong atmospheric emission. However, the absorption profile shows only marginal evidence for broad damping wings (Fig. 3) which should be easily visible for such a high column density. We suggest, therefore, that the feature most probably arises from a blend of a number of individual Lyman- absorbers. The absorbers would need to be spread over a velocity range of km sec. This relatively broad velocity range implies that this system is unlikely to be a collapsed structure (c.f. Ortiz-Gil et al. 1997), but is more likely to be an over-dense region consisting of several high column density systems. For the observed velocity range at these could be spread over a region as large as 10-15 Mpc.

Clusters of strong absorption systems similar to A-2 are relatively rarely seen, the system in PKS2000-330 (Carswell et al. 1987) being another, although that does not span as wide a velocity range as the system in Q1332+5034. Therefore, irrespective of its precise interpretation, A-2 is an intriguing system and hence worthy of more detailed study.

© Copyright Astronomical Society of Australia 1997