Full text of DOI:10.1046/j.1365-8711.2000.03453.x

Mon. Not. R. Astron. Soc. 317, 9±22 (2000)
Extended line emission around seven radio-loud quasars at redshift z , 2
R. J. Wilman,w R. M. Johnstone and C. S. Crawford
Institute of Astronomy, Madingley Road, Cambridge CB3 0HA
Accepted 2000 February 7. Received 2000 January 17; in original form 1999 October 18
A B S T R AC T
We present near-infrared spectra of seven radio-loud quasars with a median redshift of 2.1,
five of which were previously known to have Lya nebulae. Extended [O iii] l5007 and Ha
emission are evident around six objects, at the level of a few times 10216 erg cm22
arcsec22 s21 within .2 arcsec of the nucleus (;16 kpc in the adopted cosmology). Nuclear
[O ii] l3727 is detected in three of the five quasars studied at this wavelength and clearly
extended in one of them.
The extended [O iii] tends to be brighter on the side of the nucleus with the stronger, jet-
like radio emission, indicating at least that the extranuclear gas is distributed anisotropically.
It is also typically redshifted by several hundred km s21 from the nuclear [O iii], perhaps
because of the latter being blueshifted from the host galaxy's systemic velocity. Alterna-
tively, the velocity shifts could be due to infall (which is suggested by linewidths
,1000 km s21 FWHM) in combination with a suitable dust geometry. Lya/Ha ratios well
below the case B value suggest that some dust is present.
Photoionization modelling of the [O iii]/[O ii] ratios in the extended gas suggests that its
pressure is around or less than a few times 107 cm23 K; any confining intracluster medium is
thus likely to host a strong cooling flow. A comparison with lower redshift work suggests
that there has been little evolution in the nuclear emission-line properties of radio-loud
quasars between redshifts 1 and 2.
Key words: quasars: emission lines ± quasars: general.
high Faraday rotation measures (Carilli, Owen & Harris 1994,
1
I NTRO DUC TION
1997) suggest that the medium is clumpy and dense. Of particular
interest is the so-called `alignment effect', whereby the radio and
extended optical/UVemission of z . 0:6 radio galaxies are seen to
be coincident (McCarthy et al. 1987; Chambers, Miley & van
Breugal 1987); recent work by Lacy et al. (1999) suggests that
different physical mechanisms are responsible for its manifesta-
tion on different spatial scales. Similarly, Best, Rottgering &
Longair (2000a,b) have studied the emission-line properties of a
large sample of z , 1 radio galaxies: they conclude that in small
radio sources (<150 kpc in size) the kinematics and ionization
state of the line-emitting clouds are dominated by the effects of
the bow shock associated with the expansion of the radio source
through a confining medium; photoionization of the gas by the
nuclear source is more important in larger radio sources.
The processes which precipitated the steep decline in the co-
moving density of luminous quasars since the epoch z , 2 remain
poorly understood. One observational approach to the problem
proceeds through the study of the emission-line gas extending tens
of kpc from the quasar. This material is the only visible tracer of
the immediate of the quasar environment and as such its
kinematics and ionization state may yield clues to the mechanisms
which have driven the cosmological evolution of the population as
a whole, as well as the early stages of galaxy formation more
generally.
There are numerous indications that at redshift z . 0:5
powerful radio sources inhabit environments similar to the rich
clusters found locally around the luminous FR II sources Cygnus
A and 3C 295. The radio-source properties alone demand a certain
type of environment: a confining medium capable of acting as a
working surface for the formation of steep-spectrum radio lobes
To study the environments of radio-loud quasars in correspond-
ing detail is technically more difficult, as the bright unresolved
nucleus tends to overwhelm surrounding structure. Over the last
decade or more, however, we have pioneered the use of optical
long-slit spectroscopy to probe the extended emission-line regions
around radio-loud quasars out to redshift z , 1 (Fabian et al.
1988; Crawford & Fabian 1989; Forbes et al. 1990; Bremer et al.
1992). Where the emission line ratio [O iii] l5007/[O ii] l3727
can be measured for the extended gas, it can be used in
is
a basic requirement. Faraday depolarization asymmetry
(Garrington & Conway 1991), distorted/compressed radio source
morphologies at high redshift (Hintzen, Ulvestad & Owen 1983;
Barthel & Miley 1988) and the discovery of sources with very
w E-mail: wilman@ast.cam.ac.uk
q 2000 RAS

10 R. J. Wilman, R. M. Johnstone and C. S. Crawford
conjunction with photoionization models to deduce the gas
pressure. The latter is found to be consistently high ꢀnT ,
5 Â 105±1 Â 107 cm23 K at tens of kiloparsecs from the nucleus),
and an increasing function of redshift (or of quasar luminosity).
Pressure equilibrium between the line-emitting gas and any
confining X-ray halo restricts the cooling time of the hot gas to be
less than the Hubble time, suggesting that the quasars reside in
cooling flows with mass deposition rates of up to 1000 M( yr21
within 20 kpc. Such flows would have strongly influenced the
formation and evolution of both the quasar and its host galaxy (see
e.g. Fabian & Crawford 1990). This interpretation is supported by
the detection of extended X-ray emission around 3CR quasars by
Crawford et al. (1999) and by Hardcastle & Worrall (1999).
Beyond z , 1 the diagnostic lines of [O iii] and [O ii] move into
the near IR where differences in the technology and atmospheric
properties conspire to make the extension of this technique more
difficult. Fortunately, however, there is a narrow redshift window
around z ˆ 2:2 where the [O ii], [O iii]1Hb and Ha1[N ii]
complexes fall in the J, H and K atmospheric transmission bands,
respectively. We have thus obtained near-IR spectra of seven
radio-loud quasars near this redshift using the CGS4 spectrograph
on the United Kingdom Infrared Telescope (UKIRT). Studies from
the ground (Heckman et al. 1991a,b, hereafter H91a,b) and with
Hubble Space Telescope (HST) (e.g. Lehnert et al. 1999a,
hereafter L99a) have established that 100-kpc-scale Lya nebulae
are common around high-redshift quasars and a weaker analogue
of the radio-galaxy alignment effect has been found (Lehnert et al.
1999b). Nevertheless, the spectroscopic elucidation of their
properties remains in its infancy (e.g. Lehnert & Becker 1998).
The structure of the paper is as follows: in Section 2 we
describe the observations and data reduction and in Section 3
detail the extraction of the extended emission and present the
results on an object-by-object basis; in Section 4 we discuss its
kinematics, morphology, ionization state and relationship with the
radio source; Section 5 comprises a brief analysis of the nuclear
emission-line spectra in the light of lower redshift studies and
Section 6 a summary of our findings and the conclusions. The
cosmological parameters H0 ˆ 50 km s21 Mpc21; q0 ˆ 0:5 are
adopted throughout, giving a spatial scale of 8 kpc arcsec21 at
z ˆ 2:2:
2
OBSE RVAT IONS AN D DATA RED UCT ION
2.1 Target selection
In order to maximize the likelihood of detecting extended
emission, the targets were chosen primarily from those with
known Lya nebulae in the narrow-band imaging study of quasars
in H91a. For other objects found in a NED search covering the
appropriate area of the sky and redshift but not observed by H91a,
the presence of strong, narrow nuclear He ii l1640 was used as a
further selection criterion. H91b confirmed the suggestion of Foltz
et al. (1988) that this line plausibly originates in the inner parts of
such nebulae and that it is thus an indirect indicator of their
presence. Other desirable attributes for potential targets were a
resolved radio structure (especially one with a depolarization
asymmetry) and a well-constrained X-ray±optical spectral energy
distribution (SED) for use in photoionization modelling. The
sample is thus not in any sense statistically complete.
2.2 Data acquisition and reduction
The observations were made using the CGS4 spectrograph on
UKIRT on the nights of 1997 November 23±24 and 1999 June
26±27. The 256 Â 256 InSb array, 40 line mm21 grating and
300 mm focal-length camera were in place, yielding a spatial scale
of 0.61 arcsec pixel21 and a spectral resolution of ,850 km s21
FWHM (in the H band) with a 2-pixel-wide slit.
For each object we acquired a spectrum covering the [O iii]
l5007, 4959 doublet and the [N ii]1Ha complex (i.e. connecting
the H and K bands) at at least one position angle, chosen to align
with either the axis of greatest extent in published Lya maps or
along/perpendicular to any extended radio structure. When time
permitted, a J-band spectrum covering redshifted [O ii] l3727 was
also obtained. The ND-STARE mode was used along with the
conventional object±sky±sky±object nodding pattern, thus
Table 1. Target properties and observation log.
Object
Other name
z
spatial scale
(kpc/arcsec)
Band²
Exposure Slit PA
(minutes) (deg. E of N)
Seeing*
(arcsec)
Comments
1997 November 23±24
Q00171154
3C 9
2.012
8.2
H 1 K
J
H 1 K
H 1 K
J
116
90
60
60
45
46
110
0
0
0
0
0
0
0
1.4
1.3
1.4
1.3
1.5
1.3
1.3
Q02252014
Q04451097
PKS
PKS
2.037
2.11
8.2
8.1
Q08021103
3C 191
1.956
8.2
H 1 K
J
1999 June 26±27
Q16581575
Q18161475
4C57.29
4C47.48
2.173
2.225
8.0
8.0
H 1 K
H 1 K
H 1 K
H 1 K
H 1 K
J
H 1 K
H 1 K
J
52
28
60
56
56
64
36
54
45
135
146
56
45
45
90
135
135
1.5
1.1
1.0
1.2
1.1
1.2
0.9
0.9
1.0
³ with 1-pixel-wide slit
Q23381042 PKS 4C04.81 2.594
7.6
108
² H 1 K covers [O iii] l5007, 4959 and [N ii]1Ha; J covers [O ii] l3727.
* FWHM of standard star spatial profile along the slit.
³ at start of first night; slit-width changed thereafter to 2-pixel (1.2 arcsec) for rest of run.
q 2000 RAS, MNRAS 317, 9±22

Seven radio-loud quasars at redshift z , 2
11
obviating the need for separate bias and dark current frames and
permitting the computation of an external error for each pixel; it
also reduces the required accuracy of the flat-field frame.
Atmospheric absorption features were removed by ratioing with
some of the main-sequence F stars tabulated at the telescope
which were, in most cases, photometrically calibrated using
observations of faint standards.
at the end of the wavelength range and there are no arc lines there
with which to calibrate it. There was no evidence for any extended
Hb. [O ii] l3727 was typically very weak and in many cases only
an upper limit on its intensity could be extracted; where it was
detected, the fitting of nothing more than a single Gaussian was
justified at this resolution and signal-to-noise ratio, despite the true
doublet nature of this line. Errors on all quantities are the result of
propagating the Dx2 ˆ 1 parameter errors from the emission-line
fitting.
On- and off-line data reduction was performed using version
V1.3-0 of the Portable CGS4 Data Reduction package available
through Starlink. Row-by-row spectra were extracted from the
fully reduced spectral images and converted to ASCII format for
use with the emission-line fitting package qdp/plt (Tennant
1991). For the 1997 data, the figaro task sdist was used to
correct for spectral curvature prior to splitting into rows, which
had the undesirable effect of eliminating the variance array.
The target properties and observation log are shown in Table 1.
For each quasar, we give a brief introduction to the literature on
the source and describe the results of the EW analysis, which are
also illustrated in Figs 1±7. Extended [O iii] l5007 is found in six
of the objects, at the significance levels given in Table 2. The
extended surface brightness in this and other lines is computed and
listed in Table 3 and comparison made with the Lya maps of H91a
and L99a.
3
R ESULTS
3C 9 (Q00171154)
3.1 Extraction of extended line fluxes
H91a found an oval-shaped Lya nebula extending .8 arcsec
north±south and misaligned with the radio source which lies along
a position angle of 1508 (Bridle et al. 1994); a faint filament
.3.4 arcsec to the south-east coincides with a radio hotspot. We
made the first detection of extended [O iii] l5007 along a north±
south slit in 3C 9 during an earlier CGS4 run (Johnstone et al.
1993), prior to a chip upgrade and through thin cirrus cloud; our
current value for the redshift of the nuclear [O iii] ꢀz ˆ 2:021 ^
0:0009† accords well with our previous measurement ꢀz ˆ
2:019 ^ 0:001†: Fig. 1 shows that [O iii] l5007 is clearly extended
in the present data on both sides of the nucleus, especially to the
north. Extended narrow Ha is also detected in three rows but
[O ii] l3727 is generally not seen, except for very marginal
detections on nucleus ꢀz ˆ 2:019 ^ 0:003† and 1.5 arcsec to the
south of it ꢀz ˆ 2:025 ^ 0:002† (see Fig. 1). The underlying
continuum is unresolved.
One way to demonstrate the presence of extended line emission is
to plot the equivalent width (EW) of the detected line as a function
of position along the slit. Extension then manifests itself as an off-
nuclear increase in the EW if the underlying continuum originates
entirely in the spatially unresolved quasar nucleus. If, however, the
continuum is extended ± and this can be ascertained by using a
suitable point-spread function (psf) from a standard star observa-
tion ± we use a slightly more complex method: instead of
evaluating the EW with respect to the continuum measured locally
in each row, we use a so-called psf-scaled nuclear continuum
which is obtained by taking the continuum level in the row where
it peaks (defined as the nuclear continuum) and scaling it
according to the psf. The psf-scaled nuclear continuum for a given
row thus represents the continuum which would have been
measured in that row if there were no extended continuum. The
assumption that at its peak the continuum originates entirely in
the unresolved nucleus is conservative, in that where this is not the
case the method underestimates the true amount of extended line
flux. As stated below, Figs 1±7 include for each object the spec-
trum of the [O iii] doublet integrated along the slit with the nuclear
contribution overlaid, the latter being a psf-scaled version of the
profile fit to the [O iii] doublet in the nuclear row (and Hb where
it is within the range). Also shown are spectra of the extended
[O iii] doublet alone, obtained by subtracting a psf-scaled
spectrum of the nuclear row from that integrated along the slit.
The above EW procedure was used to search for extended
[O iii] l5007, followed by [O ii] l3727 and the narrow component
of Ha. Each line complex was fitted with single-component
Gaussian profiles atop a linear continuum, with line ratios set to
their theoretical values (3:1 for both the [O iii] l5007, 4959 and
[N ii] l6584, 6548 doublets) and with the velocity widths of all
(narrow) lines within a complex set equal. Except where the
continuum was spatially extended, the broad Ha width and the
ratio of the broad Ha flux to the local continuum were frozen at
the values determined from the fit to the nuclear spectrum. Where
nuclear Hb was within the wavelength range and clearly detected,
it was fitted with broad and narrow components having velocity
widths equal to those extracted from the Ha and [O iii] fits,
respectively; the centroids of both components were constrained
to be at the same wavelength, but not tied to the position of [O iii],
as the reliability of the estimated wavelength scale is questionable
H91a did not subtract the unresolved nuclear emission from
their Lya map, so a comparison with our results is not
straightforward. Nuclear Lya will contribute to their map at the
radii of interest as they report a (spatially extended/total) Lya flux
ratio of 0.2. Their lowest surface brightness contour is at 3:6 Â
10217 erg cm22 arcsec22 s21 approximately 4 arcsec north and
south of the nucleus, rising to around 4:3 Â 10216 erg cm22
arcsec22 s21 1.8 arcsec to the north. Using the Ha surface
brightness in Table 3, we deduce that Lya=Ha , 3:7 in the
extended gas at this position. Comparison with the dust-free case
B prediction of Lya=Ha ˆ 12:3 (Krolik & McKee 1978) suggests
that there is at least some dust present in the nebula. We note,
however, that very little is needed to quench Lya because of the
effects of resonant transfer in a dust/gas mixture (Fall, Pei &
McMahon 1989). Indeed, since ‰O iiiŠ=Ha . 4 around 1.4 arcsec
north of the nucleus it follows that Ha=Hb . 0:25  ‰O iiiŠ=Hb;
so the Balmer decrement may not substantially exceed the case B
value if ‰O iiiŠ=Hb , 10; as found by Boroson, Persson & Oke
(1985) for the extended gas around some quasars at z . 0:2±0:5:
The upper limit that we can place on any extended Hb does not
constrain the intrinsic reddening.
PKS 02252014
The Lya image of H91a is marginally resolved, mostly along a PA
of 1408, coinciding roughly with the direction in which the central
q 2000 RAS, MNRAS 317, 9±22

Figure 1. For 3C 9: (a) EW [O iii] l5007 versus nuclear distance along the north±south slit (each pixel measures 0.6 arcsec); (b) the integrated spectrum of the [O iii] doublet with the fit to the contribution of the
nuclear light overlaid, the latter being the profile fit to the [O iii]1Hb complex in the nuclear row (defined as that in which the continuum peaks), scaled using the psf to include nuclear light scattered into other
rows; (c) the spectrum of the extended [O iii] flux alone, obtained by subtracting from the integrated spectrum of (b) a psf-scaled spectrum of the nuclear row (the resulting line is a 10.2s detection); (d) extended
[O iii] l5007 surface brightness; (e) identified [O ii] l3727 features ± the dashed line indicates the fitted position on nucleus.

Seven radio-loud quasars at redshift z , 2
13
Figure 2. For PKS 02252014: (a) EW [O iii] l5007 versus nuclear distance; (b) integrated spectrum of the [O iii] doublet with the fit to the nuclear
contribution overlaid; (c) extended flux spectrum.
Figure 3. For PKS 04451097: (a) EW [O iii] l5007 evaluated with respect to the psf-scaled nuclear continuum, because the continuum measured directly in
each row is extended beyond the psf (see text for details); (b) integrated spectrum of the [O iii] doublet with the nuclear fit overlaid; (c) extended flux
spectrum (the line is detected at the 6.1s level); (d) extended [O iii] l5007 surface brightness
component of the radio source is extended in the radio map of
Barthel et al. (1988). A pair of non-equidistant radio lobes are
located at PAs of 1408 and 2908.
We find no evidence for extended [O iii] l5007 (see Fig. 2) and
the underlying continuum is unresolved. There is marginal
evidence for extended Ha and comparison with the Lya map of
H91a (from which the point-source contribution has not been
removed) implies that Lya=Ha , 5:6 in the extended gas
1.2 arcsec north of the nucleus, suggesting that there is some
dust associated with the gas.
ruling out the possibility that the fuzz is scattered nuclear light. The
SED of the fuzz in fact resembles that of an irregular galaxy, with
an inferred star-formation rate of several hundred M( yr21. Long-
slit spectroscopy by H91b found a linewidth of 1500 ^ 300 km s21
FWHM in the Lya nebula, with strong nuclear zabs . zem Lya and
NVl1240 absorption. Their claim that the strong, narrow He ii
l1640 arises from the inner part of the nebula would, they say, be
supported by the presence of strong [Oii] l3727 and [O iii] l5007
with widths .1000 km s21. We do indeed see relatively broad
[O iii] l5007 both on and off-nucleus (see Section 3.2). Lehnert &
Becker (1998) found similarly broad, faint extended He ii l1640
and C iii l1909 from the quasar host galaxy.
PKS 04451097
The extended continuum complicates the extended line-flux
computation as it is impossible to ascertain what fraction of the
light is truly nuclear in origin. As explained earlier in this section,
we make the assumption that, in its peak row, the continuum is
entirely nuclear in origin. The EW[O iii] l5007 points plotted in
Fig. 3 are thus calculated with respect to the psf-scaled nuclear
continuum, instead of that measured locally in each row. Owing to
The Lya map of H91a is asymmetrically extended to the south
and south-west of the nucleus, with an overall size of 12 arcsec.
Much of the radio emission originates in a knotty jet to the west-
south-west (Barthel et al. 1988). Lehnert et al. (1992) reported an
extended near-IR and optical-continuum `fuzz', with colours similar
to those of the central object (which is itself unusually red), thus
q 2000 RAS, MNRAS 317, 9±22

Figure 4. For 3C 191: (a) EW [O iii] l5007 versus nuclear distance; (b) integrated spectrum of the [O iii] doublet showing the fit to the nuclear contribution; (c) extended [O iii] spectrum (a 6.7s detection); (d)
extended [O iii] l5007 surface brightness; (e) spectra of rows with identified [O ii] l3727.

Seven radio-loud quasars at redshift z , 2
15
Figure 5. For Q16581575 at a position angle of 458; (a) EW [O iii] l5007; (b) integrated [O iii] doublet spectrum with the fit to the nuclear contribution
overlaid; (c) extended [O iii] spectrum (a 5.4s detection); (d) extended [O iii] l5007 surface brightness.
Figure 6. For Q18161475 along PA 1468: the extended [O iii] l5007 surface brightness; (b) the integrated [O iii] doublet spectrum with the fit to the nuclear
contribution overlaid; (c) extended [O iii] spectrum (a 4.6s detection); (d) VLA 6-cm radio map from Barthel et al. (1988); the grid and row numbers denote
the position of the CGS4 slit (adjacent rows are 0.6 arcsec apart) and the cross marks the position of the optical nucleus according to the latter authors
a flux calibration problem with the J-band exposure, upper limits
on EW[O ii] l3727 were converted to surface-brightness limits by
extrapolating the continuum from the H 1 K band spectra.
The [O iii] l5007 and Ha are more extended on the southern
side of the nucleus, consistent with the appearance of the Lya map
in H91a. Using the latter, we deduce upper limits on the Lya/Ha
ratio of 0.6 and 0.8 at distances of 0.9 arcsec north and 1.6 arscec
south of the nucleus, respectively. These values are more than an
order of magnitude below the case B prediction, implying that
there is some dust associated with the gas.
3C 191 (Q08021103)
Based on a slightly shorter CGS4 exposure, Jackson & Rawlings
q 2000 RAS, MNRAS 317, 9±22

Figure 7. For PKS 23381042: (a) EW [O iii] l5007for slit position angles of 908 and 1358, in the latter case evaluated with respect to the psf-scaled nuclear continuum; (b) the integrated spectrum of the [O iii]
doublet with the fit to the nuclear contribution overlaid; (c) extended [O iii] spectrum at PA 1358 (an 8.8s detection); (d) surface brightness of extended [O iii] l5007 at the two position angles; (e) J-band spectra
of the individual rows where [O ii] l3727 is identified (the dashed vertical line marks the nuclear wavelength); (f) EW [O ii] l3727 along PA 1358, evaluated with respect to the psf-scaled nuclear continuum; (g)
surface brightness of extended [O ii] l3727.

Seven radio-loud quasars at redshift z , 2
17
(1997) reported tentative evidence for extended [O iii] l5007 in
this object. The radio source is a linear structure along PA 108 with
a total extent of ,5 arcsec (Lonsdale, Barthel & Miley 1993) and
a jet-like morphology to the south. The object is not in the H91a
sample.
The EW plot of Fig. 4 confirms that [O iii] l5007 is extended,
especially to the south of the nucleus. [O ii] l3727 is seen in the
nuclear row and extended in three further rows, the spectra of
which are also shown in Fig. 4.
4C57.29 (Q16581575)
Table 2. Statistical significance of the
extended [O iii] l5007 detections.
The Lya map of H91a (from which the point source has been
subtracted) reveals a round nebula which is perhaps more
extended to the north-north-east, towards the linear radio structure
along PA 188 (Barthel et al. 1988). The HST narrow-band Lya
image of L99a shows a broad swathe of emission extending
1.5 arcsec north-east of the nucleus, as well as significant
extension to the north-west, thus motivating our choice of slit-
position angles. Fig. 5 corroborates these results by showing
extended [O iii] l5007 to the north-east. We see no evidence for
extension at the other position angle but this is perhaps due to the
much shorter integration time and the less efficient 1-pixel-wide
slit which was in use at the start of the first night.
Object
²
3C 9
10.2s
No detection
6.1s
PKS 02252014
PKS 04451097
3C 191
Q16581575
Q18161475 (PA 1468)
PKS 23381042 (PA 1358)
6.7s
5.4s
4.6s
8.8s
² The [O iii] l5007 detection significance
(in units of the standard deviation on the
underlying continuum in a 4-pixel-wide
extraction box) in the spatially integrated
spectrum after subtraction of a psf-scaled
nuclear contribution.
For comparison, the lowest surface-brightness contour in the
extended Lya map of H91a is at 1:1 Â 10217 erg cm22
arcsec22 s21 at a radius of about 4 arcsec in the eastern
Table 3. Extended emission line surface brightnesses in units of 10216 ergcm22 arcsec22 s21; a figure in the column (a, b) denotes the value in a 0.6-arcsec-
wide pixel lying at some distance r from the quasar nucleus where a < r , b (values in succesive columns of a given row correspond to points separated by
the 0.6-arcsec-pixel size); the tabulated values should not be understood as average surface brightness levels within the stated range. The slit orientations are
as indicated.
Nuclear distance along the slit in arcsec
(20.6,0)
Object
ꢀ22:4; 21:8† ꢀ21:8; 21:2†
(S)
ꢀ21:2; 20:6†
(0,0.6)
(0.6,1.2)
(1.2,1.8)
(1.8,2.4) jrj > 2:4
(N)
3C 9:
[O iii]
Ha
±
±
±
3:8 ^ 1:2
1:1 ^ 0:8
,7.3
0:9 ^ 1:0
20:8 ^ 0:9
,8.6
±
±
±
±
0:08 ^ 0:9
±
5:6 ^ 1:2
1:4 ^ 0:7
,8.5
5:8 ^ 0:9
1:2 ^ 0:6
3:8 ^ 1:2
2:8 ^ 0:9
±
,8.9
±
±
±
[O ii]
PKS 02252014:
Ha
(S)
±
(N)
±
±
±
2:1 ^ 1:3
0:8 ^ 1:2
0:7 ^ 1:1
±
±
PKS 04451097:
(S)
±
±
(N)
±
±
[O iii]
Ha
[O ii]
2:0 ^ 1:1
1:6 ^ 1:1
,2.0
2:2 ^ 1:5
1:9 ^ 1:2
,2.3
4:5 ^ 1:6
5:2 ^ 2:6
,2.8
±
±
3:7 ^ 1:5
2:7 ^ 2:3
,2.0
2:3 ^ 1:3
±
±
±
±
±
±
,2.4
±
3C 191:
[O iii]
Ha
(S)
±
±
(N)
±
±
0:5 ^ 1:6
1:9 ^ 1:0
±
6:6 ^ 1:5
2:6 ^ 2:0
1:4 ^ 0:7
8:2 ^ 2:0
3:0 ^ 3:2
±
±
±
±
7:4 ^ 1:7
20:2 ^ 2:0
1:2 ^ 0:7
20:9 ^ 1:3
2:3 ^ 1:1
±
±
±
±
[O ii]
0.8^0.6
±
Q 16581575:
[O iii]
Ha
(SW)
±
±
(NE)
±
±
±
±
20:2 ^ 0:7
20:04 ^ 0:3
±
0:6 ^ 0:6
±
±
2:1 ^ 0:9
0:3 ^ 0:5
3:0 ^ 0:7
0:5 ^ 0:3
±
±
Q 18161475:
[O iii]
Ha
(,NW)
1.8^0.7
(,SE)
±
0:4 ^ 0:2
1:9 ^ 0:6
0:2 ^ 0:3
1:1 ^ 0:8
±
±
0:3 ^ 0:4
1:0 ^ 0:7
±
0:2 ^ 0:5
0:4 ^ 0:2
±
±
²
±
±
Q 18161475:
[O iii]
Ha
(,SW)
±
±
(,NE)
±
±
±
0:3 ^ 0:3
±
20:5 ^ 0:4
20:5 ^ 0:8
±
±
0:6 ^ 0:6
0:7 ^ 0:7
0:1 ^ 0:3
0:9 ^ 0:6
0:6 ^ 0:4
0:9 ^ 0:5
±
PKS 23381042:
[O iii]
Ha
[O ii]
(NW)
±
±
(SE)
±
±
±
2:1 ^ 0:9
6:6 ^ 1:4
2:3 ^ 0:9
5:9 ^ 1:5
±
±
9:6 ^ 1:3
3:8 ^ 1:9
2:0 ^ 0:9
4:1 ^ 1:3
±
,4.3
±
±
±
1:6 ^ 0:7
,2.90
±
±
±
2:0 ^ 1:0
±
PKS 23381042:
[O iii]
Ha
(W)
±
±
(E)
±
±
1:0 ^ 0:4
±
1:1 ^ 0:9
1:0 ^ 0:8
±
±
±
±
5:8 ^ 0:9
9:3 ^ 1:4
2:5 ^ 1:0
3:1 ^ 1:2
±
±
² Q 18161475 shows extended [O iii] l5007 at jrj > 2:4 arcsec along the radio axis (PA 1468), with values of 1:2 ^ 0:7; 1:2 ^ 0:5 and 1:0 ^ 0:4 Â 1016
erg cm22 arcsec22 s21 at r ˆ 24:2, 12.4 and 13.0 arcsec from the nucleus, respectively.
q 2000 RAS, MNRAS 317, 9±22

18 R. J. Wilman, R. M. Johnstone and C. S. Crawford
hemisphere. We thus estimate that Lya=Ha , 4 in the extended
gas around 1 arcsec north-east of the nucleus. Comparison with
the dust-free case B prediction that Lya=Ha ˆ 12:3 suggests that
there is some dust present.
either concurrently with or prior to the quasar phase itself. This is
also suggested by the presence of dust associated with the gas, as
evidenced by Lya=Ha ratios well below the case B value.
4.1 Kinematics and morphology of the extended line
emission
4C47.48 (Q18161475)
The noise level of the present data does not permit us to examine
the kinematic structure of the gas or its morphological association
with the extended radio structure in spatially resolved detail. In
fact, nothing more than the extraction of a single, integrated
spectrum of the off-nuclear light can really be justified for
kinematic purposes. We thus fitted a single kinematic component
to the [O iii] doublet of each of the off-nuclear spectra, to
determine an average velocity offset (from the nuclear emission)
and the velocity dispersion. The results are shown in Table 4.
Whilst the errors for individual objects are large, the extended
gas is on average redshifted by a few hundred km s21 relative to
the nuclear emission. Furthermore, although the errors are larger
still, we found a velocity offset of the same sign on both sides of
the nucleus within a given object. This tendency for the extended
[O iii] to be redshifted from the nuclear [O iii] can be seen in Figs
1±7, where we show for each quasar an integrated spectrum of the
[O iii] doublet with the fit to the spatially unresolved nuclear
This quasar is not in the H91a sample, but we included it on
account of its extended radio structure (Barthel et al. 1988),
complete with depolarization asymmetry between the jet and
counter-jet sides (Garrington, Conway & Leahy 1991). We
acquired H 1 K band spectra along and perpendicular to the
radio axis (PA 1468 and 568, respectively) and also along PA 458.
There was only time to do a single PA in [O ii] l3727.
Extended [O iii] l5007 and Ha are seen at both PA 1468 and
568, with total [O iii] fluxes of 7:0 ^ 3:0 and 1:9 ^ 0:8 Â
10216 erg cm22 21; respectively (i.e. it is brighter along the
s
radio axis). Since the error on the fitted continuum level
completely dominates the uncertainty in the EW in some of the
rows at large nuclear distances, we do not plot it in Fig. 6. For
comparison with the extended [O iii] l5007 surface-brightness
plot, we show a VLA 6-cm radio map of the object, reproduced
from Barthel et al. (1988): note that [O iii] is present at the
position of the fainter, south-eastern lobe (rows 100 and 101), but
absent from that on the north-western side (rows 90 and 91). There
is no extended [O iii] l5007 along PA 458 nor [O ii] l3727 of any
kind.
Table 4. Kinematic properties of the off-nuclear gas.
Object
PA
(deg)
DVext-nuc
(km s21
*
)
FWHM
(km s21
)
PKS 23381042
1320
2520
3C 9
PKS 02252014
PKS 04451097
0
0
0
250 ^ 100
²
200 ^ 220
520
The Lya map of H91a has a north-west/south-east orientation,
with brighter emission on the south-eastern side. The radio source
is a smooth bent triple with lobes to the west and south-east within
2 arcsec of the nucleus (Barthel et al. 1988). L99a interpret the
spatial relationship between this distorted structure and the
extended Lya in their HST narrow-band image as evidence for
a `jet±cloud' interaction. The EWs of [O iii] l5007 along the two
position angles listed in Table 3 are shown in Fig. 7. That along
PA 1358 is computed with respect to the psf-scaled nuclear
continuum, owing to the presence of extended continuum at this
PA (both H91a and L99a report that the rest-frame UV is well-
resolved). There is clear evidence for extended [O iii] l5007 and
Ha, especially to the north-west, south-east and east of the
nucleus. There is also strong evidence for extended [O ii] l3727,
as the EW plot of Fig. 7 demonstrates for PA 1358 (the
continuum beneath [O ii] l3727 is also extended). Individual
spectra of the four rows with [O ii] l3727 detections are also
shown in Fig. 7.
²
1520
1030
2730
1970
2610
3C 191
0
170 ^ 230
240 ^ 240
610
1540
2680
Q16581575
Q18161475
45
1120
11300
21260
146
56
90
380 ^ 350
180 ^ 300
290 ^ 130
1260
Unresolved
1390
2430
PKS 23381042
1180
1270
2300
135
120 ^ 100
980
* Velocity of the extended [O iii] emission with respect
to that in the nucleus.
² The extended flux is not visible above the noise.
Comparison with the Lya map of H91a yields upper limits on
the extended Lya=Ha ratio of 7, 0.8, 0.7 and 1.3 at distances of
0.9 arcsec west, 1.5 arcsec east, 1.4 arcsec north-west and
1.0 arcsec south-east of the quasar, respectively, suggesting that
there is some dust present.
4
DISCUS SION
Before considering the detailed properties of the extended line
emission, we mention the rather obvious point that the mere fact
that it is seen from a coolant such as [O iii] implies that the
galactic-scale environment of the quasar has undergone some
metal enrichment. An episode of star formation has thus occurred,
Figure 8. The extended±nuclear [O iii] l5007 velocity difference
(DVext-nuc) plotted against the nuclear [O iii] l5007-Ha velocity
difference (DV[O iii]-Ha).
q 2000 RAS, MNRAS 317, 9±22

Seven radio-loud quasars at redshift z , 2
19
component overlaid: residual emission tends to appear redward of
the fit. One possible explanation for this lack of kinematic
continuity is that the nuclear [O iii] is blueshifted with respect to
the systemic redshift of the galaxy at which the bulk of the
extended emission arises.
3C 9 and PKS 02252014 (in the latter we see no extended [O iii]
l5007 along a north-south slit position). H91a reported that such a
shared asymmetry also exists in the extended radio and Lya
emission but, owing to the greater extinction suffered by Lya on
the far side of the nebula, they could not determine whether this
was genuinely owing to the line-emitting gas being distributed
around the quasar in an intrinsically anisotropic fashion. That the
less-dust-sensitive [O iii] and Ha emission are at least as
asymmetric as the Lya strongly suggests that it is.
As stated by H91a, an intrinsically anisotropic gas distribution
is in line with theoretical models for galaxy formation (e.g. Rees
1988), as the Hubble time at this redshift would scarcely have
been long enough to permit the establishment of a symmetric gas
configuration in such a massive halo. Models in which quasar
activity is triggered by galaxy interactions (e.g. Calberg 1990) also
predict anisotropic gas distributions. McCarthy, van Breugal &
Kapahi (1991) found a similar asymmetry in powerful radio
galaxies, with the extended optical line emission virtually always
being brighter on the side of the closer radio lobe. There are hints
(in e.g. Q18161575 in Fig. 6), of a more detailed correspondence
between the extended [O iii] and the radio plasma, but an in-depth
astrophysical analysis thereof requires near-IR spectroscopy on 8-
m-class telescopes. Such correlations could be accounted for
directly if the line emission were powered by shocks associated
with the radio source, as found by Best et al. (2000a,b).
In this connection, there have been several studies of the
velocity shifts between quasar nuclear-emission lines of different
ionization; using a sample of 160 quasars, Tytler & Fan (1992)
found that each ultraviolet emission line has a well-defined mean
velocity with respect to a systemic value defined by Hb,
increasing roughly in the order of increasing ionization to 2454 ^
37 km s21 for He ii l1640. They also confirmed the result of
Gaskell (1982) that in low-z quasars and Seyfert galaxies, the
Balmer and narrow-line redshifts agree with one another to within
100 km s21. Wilkes (1986), however, found the the [O iii] l5007,
4959 lines were blueshifted by a mean velocity of 220 ^
150 km s21 from Hb. Applied to our sample, the latter result
could account for the velocity offsets between the extended and
nuclear [O iii] l5007. To investigate this hypothesis further, we
measured the velocity of nuclear [O iii] l5007 relative to Ha, for
comparison with the DVext-nuc values in Table 4, as shown in Fig.
8. Despite the large errors, the sense of the apparent trend is
consistent with an interpretation in which the nuclear [O iii]
l5007 is blueshifted from both the extended [O iii] l5007 and the
nuclear Ha by comparable amounts.
Alternatively, if the nuclear [O iii] l5007 is produced at the
systemic velocity, the tendency of the extended emission to be
redshifted relative to it could instead be due to gaseous infall
towards the quasar. In this model, dust between the line-emitting
clouds would be invoked to obscure those on the far side which
would otherwise appear blueshifted. Evidence for infall is
provided by the large linewidths in the extended gas ± our values
are compatible with those measured by H91b for the off-nuclear
Lya (1000±1500 km s21 FWHM) in some of these quasars and in
others near this redshift. Such large linewidths, they argued, result
either from infall into the potential well of a very massive galaxy
or from interaction with the radio-emitting plasma, but they did
not find that the more kinematically disturbed regions of Lya
emission were associated with the strongest radio emission. As we
noted earlier, however, L99a found evidence from HST data for a
`jet±cloud' interaction in PKS 23381042: they demonstrated that
the cloud responsible for the Lya emission is massive enough to
deflect the radio jet and to survive for long enough after the
collision to emit at the observed epoch, several Myr later. Our
present data provide little new information on the detailed relation
of the extended line emission to the radio structures. The 1997
observations were at a single position angle and the line emission
in two of the 1999 objects, Q16581575 and PKS 23381042, was
already known to align more closely with the radio structure than
perpendicular to it (H91a; L99a). Our results on Q18161475 are
qualitatively similar, with the strongest extended emission being
along the linear radio axis, as remarked above. Concerning dust,
we have noted that while the Lya=Ha values in the extended gas
are typically well below the case B dust-free prediction, this does
not necessarily indicate substantial amounts of reddening. Where
Hb is within the wavelength range, upper limits on its extended
flux do not place any constraints on the extinction.
4.2 The [O iii]/[O ii] ratio and the extended gas pressure
A key objective of this work was to measure the ‰O iiiŠ=‰O iiŠ ratio
in the extended gas as a diagnostic of the pressure, for comparison
with the lower redshift studies listed in Section 1. As mentioned in
these papers, the frequent occurrence of high-pressure line-
emitting gas around radio-loud objects requires that the warm
clouds be long-lived; this in turn suggests that they are pressure
confined by some hotter medium (otherwise they would disperse
rapidly on a sound-crossing time), an obvious candidate being a
medium similar to the hot X-ray-emitting gas found in clusters of
galaxies (the ICM). In the light of the findings of Section 4.1, it is
likely that, in those objects where the slit is aligned essentially
along the radio axis (i.e. 3C 191, Q18161475 and PKS
23381042), the line-emitting clouds are compressed by passage
through shocks associated with the radio jets and the pressures so
calculated are not representative of conditions in the surrounding
medium (see e.g. Best et al. 2000b). To compute the pressure, we
adopt a model in which ionization-bounded (optically thick)
clouds are subject to the photoionizing continuum of the central
quasar, so the neglect of any in situ sources of ionization (e.g.
shocks from the radio jet) results in the derived pressures being
lower limits on the actual values. A detailed discussion of the
reliability of these assumptions may be found in Bremer (1993).
We note that the derived pressures would increase if an
extinction correction were applied and decrease if the true nuclear
distance to the clouds were used, as opposed to the projected
value.
We have information on the ‰O iiiŠ=‰O iiŠ ratio in the extended
gas for four of the seven quasars, although for one of them ± PKS
04451097 ± it is wholly in the form of lower limits on the line
ratio. The measured ‰O iiiŠ=‰O iiŠ values are also subject to
uncertainty, for the [O iii] and [O ii] fluxes are derived from
separate long-slit spectra, which may not sample the same part of
the object and between which there may be flux-calibration
On a global level, where the slit is aligned in the general
direction of the extended radio structure, the extended [O iii] tends
to be brighter on the side of the nucleus with the stronger, jet-like,
radio emission, as in PKS 04451097, 3C 191, Q18161475,
Q16581575 and PKS 23381042. The only exceptions to this are
q 2000 RAS, MNRAS 317, 9±22

20 R. J. Wilman, R. M. Johnstone and C. S. Crawford
Figure 9. Radial variation along the slit of the ‰O iiiŠ=‰O iiŠ ratio in the four quasars for which we have such information, together with the predictions of
constant pressure cloudy photoionization models which are labelled with the values of the total gas pressure to which they correspond (in units of cm23 K).
differences. To investigate the latter we have compared the
observed J and H band nuclear continuua for each quasar and
found that for each of 3C 9 and 3C 191, the one matches well the
extrapolation of the other; for PKS 23381042, however, the `raw'
‰O iiiŠ=‰O iiŠ values have been increased by a factor of 2.25 as the
J-band continuum exceeds the extrapolation by this factor (which
is not surprising since the ratioing star used for the J-band
exposure was not flux calibrated against a faint standard). Recall
that the J-band spectrum of PKS 04451097 could not be flux
calibrated in the usual manner. We are not able to perform a
correction for intrinsic dust extinction.
X-ray luminosities from Worrall et al. (1987); for PKS
04451097, we take U, B, R and K photometry from Lehnert
et al. (1992) and H91a, along with a ROSAT X-ray flux (Siebert
et al. 1998), to obtain TBB ˆ 7:2  104 K; aox ˆ 21:0; auv ˆ 21
and ax ˆ 21; similarly, for PKS 23381042 we find, from B-band
ꢀ
photometry (H91a) and an HST flux density at lrest ˆ 1520 A
(L99a), that this narrow portion of the SED is well matched by the
default parameter values.
For each object, we ran a grid of constant pressure cloudy
models for clouds at various radii from the quasar with different
values of the hydrogen density at the exposed cloud face. The
results are shown in the plots of Fig. 9, where the cloudy model
loci are labelled with the value of the gas pressure (ngasTgas) to
which they correspond. With the exception of PKS 23381042
(where in any case the neglect of in situ ionization associated with
the jet±cloud interaction renders the derived pressure a lower
limit), our pressure measurements are equal to the maximum
possible values that could be maintained at these radii by an
isobarically cooling, pressure-confining ICM in an isothermal
potential with a line-of-sight velocity dispersion slos in the range
300 , slos , 400 km s21 (see Bremer et al. 1992 for details); the
majority of the limits on the pressure are also consistent with such
a high-pressure environment, but do not otherwise impose strong
constraints on the gas properties. Our values (and limits) are
comparable with the pressures measured by Bremer et al. (1992)
at slightly larger radii (,20 kpc) around some radio-loud quasars
at redshift z , 1 and thus not obviously inconsistent with their
conclusion that the most dramatic pressure evolution seen so far is
the strong decrease between redshift z , 1 and the present day
(see their fig. 12).
Version 90.05 of the photoionization code cloudy was
employed (Ferland 1996), using the `AGN' model continuum
therein, which comprises an exponentially cut-off `Big Bump'
component and an X-ray power law:
fn ˆ na expꢀ2hn=kTBB† expꢀ2kTIR=hn† 1 ana
uv
:
ꢀ1†
x
The coefficient a is adjusted by the code to produce the correct
Ê
X-ray (2 keV) to optical (2500 A) spectral index, aox, for the case
where the Big Bump does not contribute to the emission at 2 keV.
The default parameter values, representative of a `typical AGN',
are TBB ˆ 1:5  105 K; aox ˆ 21:4; auv ˆ 20:5; ax ˆ 21 and
kTIR ˆ 0:01 Ryd: The X-ray power law is added only for energies
greater than 0.1 Ryd and above 100 keV the continuum is assumed
to fall off as n23. Where available, literature information on the
quasars was used to adjust the parameters TBB, aox, auv and ax to
reconstruct the observed portions of the SEDs. The parameters
were otherwise left at their default values. For 3C 9 and 3C 191,
we take aox values (of 21.478 and 21.405, respectively) and
q 2000 RAS, MNRAS 317, 9±22

Seven radio-loud quasars at redshift z , 2
21
Table 5. Nuclear emission-line fluxes.
the gaseous environment within a projected radius of ,20 kpc of
the quasar.
Object
[O iii] l5007 [O ii] l3727
[O iii]/[O ii]
First, the mere existence of extended [O iii] emission and the
dust associated with it implies that the galactic-scale environment
of the quasar has already been enriched by an episode of star
formation.
3C 9
19:2 ^ 2:3
23:8 ^ 5:9
26:2 ^ 4:4
74:4 ^ 5:0
16:7 ^ 1:2
9:7 ^ 2:3
7:5 ^ 3:4
±
,4.9
9:5 ^ 2:1
±
,1.5
2:6 ^ 1:2
±
.5.3
7:8 ^ 1:8
±
.6.5
PKS 02252014
PKS 04451097
3C 191
Q16581575
Q18161475
PKS 23381042
Secondly, we found that the extended [O iii] tends to be brighter
on the side of the nucleus with the stronger radio emission,
indicating that the extended gas is distributed anisotropically and
perhaps in some cases also compressed and shock ionized through
interaction with the radio plasma.
56:7 ^ 9:0
14:6 ^ 2:0
8:8 ^ 1:8²
Fluxes are in units of 10216 erg cm22 s21; where more than one
PA was observed in [O iii], the listed value is the mean of the
measurements.
² In deriving this figure, the `raw' flux ratio was increased by a
factor of 2.25 to take account of the flux-calibration mismatch
between the J- and H-band spectra, as described in Section 4.2.
Thirdly, on a global scale, the extended [O iii] is typically
redshifted by a few hundred km s21 from the nuclear [O iii]. By
comparison with the measured velocity difference between the
nuclear [O iii] and Ha, we believe that this is probably due to the
nuclear [O iii] being blueshifted by comparable amounts from a
systemic value defined approximately by both the extended
emission and the nuclear Ha. We cannot, however, rule out an
alternative model involving gaseous infall coupled with the effects
of selective dust extinction.
5
T H E N UC L E AR SP E C T RA
Although we have hitherto been concerned with the extended
emission around the quasars, their nuclear spectra also merit
attention in the light of recent work on radio galaxies and quasars
at lower redshift. Jackson & Rawlings (1997) found that radio
galaxies and quasars at z . 1 lie on essentially the same
correlation between the [O iii] and extended 178-MHz radio
luminosities, whereas at lower redshift quasars had been found to
be more [O iii] luminous; this finding has implications for quasar/
radio-galaxy unification schemes. Similarly, Willott et al. (1999)
used the 3C and (much fainter) 7C surveys to deduce that the
[O iii] and [O ii] luminosities of low-redshift radio galaxies
depend primarily on the radio power rather than redshift.
Tadhunter et al. (1998) reported that the ‰O iiŠ=‰O iiiŠ versus
L[O iii] anti-correlation which exists for radio galaxies at z , 0:2
(Saunders et al. 1989) breaks down at higher redshift ꢀ0:5 , z ,
0:7† and similar conclusions were reached by Jackson & Rawlings
(1997). Our present data give some indication of the position of
higher redshift quasars on these correlations.
Fourthly, for four of the quasars we have information on the
‰O iiiŠ=‰O iiŠ ratio in the extended gas. This was used in
conjunction with cloudy photoionization modelling to place
constraints on the gas pressure, assuming that the radiation from
the quasar itself is the only source of ionization. We cautioned,
however, that such a scenario may not hold in all cases in view of
the observed association between the radio plasma and the
emission-line gas. With the exception of PKS 23381042, we
measure gas pressures (or limits thereon) which are comparable
with the maximum pressure which could be maintained at these
radii by any isobarically cooling ICM. This suggests that such an
ICM would host a strong cooling flow, with a mass-deposition rate
high enough to significantly influence the fuelling of the quasar,
as well as the formation of the host galaxy (see Fabian &
Crawford 1990). Future observations with Chandra and XMM are
expected to reveal such ICMs directly through their X-ray
emission. The case of A3581, however, illustrates that emission-
line spectroscopy may continue to provide a complementary
pressure diagnostic for the environments of high-redshift quasars;
X-ray observations by Johnstone, Fabian & Taylor (1998) of this
z . 0:02 poor cluster (containing the radio galaxy PKS
14042267) show that despite its low temperature (,1:5±2:0 keV†
and relatively low luminosity (,2  1042 erg s21†; its mass-
The nuclear [O iii] l5007 and [O ii] l3727 fluxes and
‰O iiiŠ=‰O iiŠ ratios are tabulated in Table 5. When placed on
Figs 4 (nuclear L[O iii] versus extended 178±Mhz radio luminosity,
L178 MHz,ext) and 7 ꢀ‰O iiiŠ=‰O iiŠ versus L178 MHz,ext) of Jackson &
Rawlings (1997), our data occupy the same regions as their lower
redshift quasars (after 3C 191 and the radio galaxy 3C 257 at
z ˆ 2:48; their highest redshift object is the z ˆ 1:681 radio
galaxy 3C 222; the mean redshift of their quasars is z ˆ 1:37†:
L178 MHz,ext is considered to be a good isotropic indicator of the
power of the central engine, for radio galaxies and quasars, and
was estimated for our objects using data in Garrington et al.
(1991), Barthel & Lonsdale (1983), Barthel et al. (1984),
Drinkwater et al. (1997), Laing, Riley & Longair (1983) and
Reid et al. (1995).
deposition rate is as high as ,80 M( yr21
:
AC KN OW L E D GM E NT S
UKIRT is operated by the Joint Astronomy Centre on behalf of the
United Kingdom Particle Physics and Astronomy Research
Council. RJW and RMJ thank PPARC for financial support,
CSC the Royal Society. Kelvin Wu is thanked for assistance
during the 1997 observing run. The anonymous referee is thanked
for helpful comments. This research has made use of the NASA/
IPAC Extragalactic Database (NED).
This finding is consistent with there having been little evolution
in the emission-line properties of radio-loud quasars between
redshifts z , 2:2 and z , 1:4: We do, however, caution that it is
based on a small, statistically incomplete, sample of objects.
6
SU MMARY A ND CO NCL USIONS
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