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Astron. Astrophys. 333, 841-863 (1998)
3.
Comments on individual objects
Here, we briefly summarize spectroscopic data previously obtained
on our targets and indicate the main results provided by the new
spectra.
![[TABLE]](img31.gif)
Table 3.
Absorption lines detected in the spectrum of PKS 0454+039
3.1. EX 0302-223
Metal-rich absorption systems have been mentioned for this object
at (Mg II: Bergeron,
unpublished) and (Fe II and
Mg II: Petitjean & Bergeron 1990). The FOS spectrum
(Fig. 1), clearly shows that the Ly line
from the latter is damped and reveals several strong features from
C II, C IV, N I,
O I, Si II, Si III and
Si IV. No less than four new metal systems are
detected. In agreement with the prediction made in Paper I, relatively
strong lines from Fe II and Mg II are
seen at a redshift , similar to that of a bright
spiral galaxy located kpc from the QSO
line of sight. Second, a strong C IV doublet together
with Ly is present at . In
addition to Ly , Ly and Ly
the FOS spectrum shows weak features from
C II, C III, Si II and
Si III at ; this system induces
a Lyman edge near 2120 Å which is clearly apparent in the
IUE spectrum (Lanzetta et al. 1995). On the other hand, no convincing
line is seen from the Mg II
system (the line at 2371 Å could be Al II
1670 at , but this feature seems to be too
strong given that we do not detect Fe II 1608).
Finally, a narrow high ionization system with strong
O VI lines is detected at . The
HST data do not confirm the and 0.9874
candidate damped Ly lines proposed by Lanzetta
et al. (1995) (the former turns out to be Ly at
1.3284).
![[FIGURE]](img43.gif) |
Fig. 1.
FOS spectrum of EX 0302-223 (G270H). Long tick marks correspond to absorption lines from the DLAS
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3.2. PKS 0454+039
Before this study, two absorption systems were known in this
object, at and 1.1537 (Burbidge et al. 1977,
Caulet 1989; Steidel & Sargent 1992). Steidel et al. (1995) have
shown that the first one is a low metallicity (about 1/10 solar) DLAS,
as indeed suggested by the strength of Mg II and
Fe II lines, while in the second system, the Ly
line is not damped. More than twenty metal lines
are seen at together with a Lyman edge near
1700 Å (Fig. 2). The Si II 1304 line is
definitely blended with another (Ly -only) line
since i) it appears too strong with respect to e.g.
Si II 1260 and ii) the match in redshift is not
satisfactory. In addition to several metal lines from
Si II, Si III, Si IV,
C II and C III, the
system displays a beautiful set of 9 lines from
the Lyman series ending with a partial Lyman edge; the presence of
N V and O VI lines in this system
remains uncertain. One additional motivation for observing this QSO is
the presence of two intervening galaxies detected by Steidel et al.
(1993). The closest one is a dwarf star-forming galaxy at
from which we do detect Mg II
absorption. The second galaxy is a more luminous one at
and kpc which
could induce C IV absorption; no lines are seen from
this galaxy but we detect a new C IV doublet at
.
![[FIGURE]](img51.gif) |
Fig. 2.
Same as Fig. 1 for PKS 0454+039 (G190H and G270H spectra)
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3.3. 3C 196
The 21 cm absorption system at is known
to display very strong associated Fe II and
Mg II lines as well as Mn II and
Ca II (Foltz et al. 1988; Boissé & Boulade
1990). An additional system is present at . The
G160L HST data presented by Cohen et al. (1996) show that,
unfortunately, the latter produces a Lyman edge nearly coincident with
the Ly line at , which
renders the determination of very difficult. An
additional source of uncertainty in the analysis is related to the
possible contribution of scattered light which makes the zero of the
intensity scale ill defined. Our new (post-COSTAR) spectrum, although
of lower integration time, is of interest in this regard. In order to
perform a quantitative comparison, we retrieved from the HST archive
the spectrum obtained in 1992 and analyzed by Cohen et al. (1996).
Using the few narrow lines detected at either ,
0.437 or 0.871 (Fig. 3), we measure shifts of 14 and
6 Å in the wavelength scales of the late and new spectrum
respectively (these values are not accurate but the relative shift of
8 Å is well constrained by the data). Once corrected, the
two spectra appear in quite good agreement but a systematic difference
is seen in the blue wing of the Ly emission line
(Fig. 3). If not instrumental, such an effect could be due to
variable Ly absorption from gas ejected by the
QSO; the time elapsed between the two observations is 2.05 yr and
during that interval the amount or ionization degree of the gas may
have changed (see e.g. Schartel et al. 1997 for another example of
variable absorption). An alternative possibility is intrinsic emission
line variability. Variable BAL-type absorption is supported by two
facts: i) the gas responsible for the narrow
absorption (to which the higher velocity gas is probably associated)
is known to cover only partially the broad line region (Cohen et al.
1996) and ii) only a small variation of of
about cm-2 is needed to
account for the strength of the effect (assuming optical
thinness).
![[FIGURE]](img60.gif) |
Fig. 3.
G160L spectra of 3C 196 obtained in 1994 as part of our program (thick line) and in 1992 by Cohen and collaborators (thin line) after correction of the wavelength scale (see text). The main absorption features from the systems at (DLAS) and are indicated (thick and thin tick marks respectively). Note the difference between the two spectra in the blue wing of the Ly emission line
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3.4. Q 1209+107
The G160L FOS spectrum (Fig. 4), although of relatively poor
S/N ratio, provides significant information on the already known metal
systems at , 0.6295 and 1.8434. First, these
data confirm that the 0.6295 system is damped (see Sect. 4.1.4);
additional narrow absorptions (Ly and
N I 1200) as well as a Lyman break are detected at this
redshift. Ly at 0.3930 is also present and there
are a few other possible features at 1.8434 (O III 702
at 1995 Å and O III 833 at
2369 Å).
![[FIGURE]](img63.gif) |
Fig. 4.
G160L spectrum of Q1209+107
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3.5. PKS 1229-021
This object has already been the subject of several detailed
optical studies. In particular, the high resolution data published by
Lanzetta & Bowen (1992) suggest a high metallicity for the
intervening gas since strong Mn II lines are detected.
We indeed find a large number of metal absorptions from the system at
. In 1991, one of us observed this object with
the IUE in order to detect the damped Ly line
and determine the H I column density; surprisingly,
near the expected wavelength of this feature, a cut-off was seen (this
IUE spectrum is shown in the catalog of Lanzetta et al. 1993). Steidel
et al. (1994a) detected a Mg II doublet at 0.7570 and
proposed that this system is responsible for the observed Lyman edge.
Our data indicate that this Mg II doublet belongs to an
extensive metal line system with absorptions from
Si II, Si III, Si IV,
C IV, N V and O VI. We
detect an additional C IV system at
. Furthermore, a strong Ly
line is seen at with several associated lines
from the Lyman series; a careful examination of the optical data
published by Steidel et al. (1994a) suggested the presence of weak
associated Mg II lines near 5120 Å.
Measurements performed on the spectrum that C. Steidel kindly
communicated to us confirm that shallow Mg II
absorption is indeed present (the 2796 Å line is seen at
Å and with
Å). On the basis of our higher resolution and better S/N
ratio UV data, we find that the partial cut-off near 1670 Å
is in fact due to this system. Fortunately, the
damped Ly line at can
nevertheless be seen, superimposed onto the attenuated continuum
(Fig. 5).
![[FIGURE]](img69.gif) |
Fig. 5.
Same as Fig. 1 for PKS 1229-021 (G190H and G270H spectra)
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3.6. 3C 286
We do not detect any additional narrow metal system in the new FOS
spectrum (Fig. 6), which makes the line identification much
easier for this QSO than for the other ones observed at high
resolution. The profiles of the O VI,
N V and to a lesser extent, of the Ly
and C IV emission lines suggest
the presence of broad absorption from highly ionized gas at
. In particular, two sharp edges are seen near
1925 and 2310 Å which, when attributed to the
O VI and N V doublets, correspond to
about the same redshift, , that is an infall
velocity of 2700 km s-1 relative to the QSO. From
the DLAS, we detect several new (mostly low-ionization) species in
addition to those - Fe II, Mg II,
Mg I, Zn II, Cr II and
Ca II - already seen by Meyer & York (1992) and
Cohen et al. (1994). Given the strength of the Ly
line, the C IV doublet is
remarkably weak; the second (1551 Å) doublet line can
barely be seen. C II 1335 lies just at the red end of
the Ly emission line and its equivalent width
strongly depends on the adopted shape for the adjacent continuum
( Å in the normalized spectrum presented
in Fig. 17). Weak N I 1200 and
Si III 1206 absorption can also be seen in the blue
wing of the damped Ly line but their
significance is difficult to assess quantitatively. Doublets from
O VI, N V and Si IV are
not detected, with good upper limits.
© European Southern Observatory (ESO) 1998
Online publication: April 28, 1998
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