Astron. Astrophys. 332, 514-522 (1998)

3. Results

3.1. The longslit spectrum of PKS 0445+097

We oriented the slit along a position angle such that the spectrum would obtain the redshift of the nearby (in projection) companion located approximately 1.8" from the quasar nucleus seen in the HST image of Lehnert et al. 1997a. Using the nuclear HeII 1640 and CIII] 1909 emission lines, we estimate the redshift of the quasar to be 2.1083 0.001. The other strong lines in the spectrum, namely, CIV 1549 and MgII 2800, had profiles that were severely affected by absorption lines. Inspecting the extended emission of the quasar reveals that this nearby object to the southeast of PKS 0445+097 is an intervening absorber galaxy (Fig. 1). The extracted spectrum reveals three identifiable lines with central wavelengths of: 6298.9Å, 6853.1Å, and 7110.6Å. We note however that the line at 6298.9Å is very close in wavelength to the telluric [OI] 6300 line. Although the sky subtraction appears to be good, it is possible that this line is influenced by inadequacies in the night sky subtraction. The lines are detected at the 5 , 30 , and 8 level respectively. We identify these lines as [NeV] 3426, [OII] 3727, and [NeIII] 3869 which implies a redshift of z=0.8384 0.0002 (where the uncertainty in this determination includes the random error from each individual line). The lines are not resolved at the low resolution of the spectrum. From the nuclear spectrum of PKS 0445+097, we identify a single absorption line at 5147.1 1Å, which we identify (as Barthel et al. 1990 did also) as MgII 2800 absorption at z=0.8396 0.0004. Barthel et al. 1990, who had a higher spectral resolution than the data presented here, measured z=0.8392 for this absorption line system, which is within the 1 uncertainty of our measurement. Calculating the velocity difference between the absorption line system and the emission line of the galaxy, we find a velocity offset of 200 80 km s^-1. Moreover, the relative fluxes in the lines give the following ratios relative to [OII]: 0.2 0.2 and 0.3 0.1.

Fig. 1. The spectrum of the intervening absorber 1.77" from the nucleus of PKS 0445+097. This spectrum is a result of extracting a region centered 1.6 arc seconds from the nucleus and over a region 1 arc second in diameter. We have identified three lines in this spectrum, [NeV] 3426 at 6298.9Å, [OII] 3727 at 6853.1Å, and [NeIII] 3869 at 7110.6Å which imply a redshift of 0.8384 0.0002. The identification and strength of the [NeV] 3426 line might be influenced by the strong telluric line of [OI] at 6300Å.

In addition to the flux associated with the intervening absorber, we also see extended flux that is apparently associated with the quasar. Because the southeastern side of the quasar is "contaminated" with the emission from the intervening absorber, we have extracted a spectrum whose center is about 2.3" from the brightest quasar emission and is a sum of about 7 CCD rows ( 1.5"). We display the extracted spectrum of the fuzz on the northwest side of the nucleus in Fig. 2. The two obvious lines are HeII 1640 and CIII] 1909. Due to falling sensitivity of the chip, the bad weather conditions and for the case of the MgII line, the strong night sky emission, we were unable to obtain high signal-to-noise information about the possibility of extended CIV 1549 and MgII 2800. We find that the HeII 1640 line is relatively narrow (FWHM=1000 200 km s^-1) and that the profile of the CIII] 1909 line is much broader (FWHM=2200 600 km s^-1). For the quasar nucleus, we find that the lines broader still, FWHM(HeII 1640)=2400 km s^-1 and FWHM(CIII] 1909)=5500 km s^-1. The width of the extended HeII and CIII] lines is comparable to the width of extended Ly measured by Heckman et al. 1991b who measured about 1500 km s^-1 for the full width at half maximum. The central wavelengths of the extended HeII and CIII] imply a redshift of 2.1087 and 2.1058 respectively, in fair agreement with the redshift estimated from the nuclear emission lines. Moreover, we find that the ratio of HeII 1640/CIII] 1909 0.55. For comparison, a rough estimate of the ratio for the quasar nucleus is HeII 1640/CIII] 1909 0.13. Estimating the signal to noise near the location of the undetected CIV 1549, we find that the 3 upper limit to the strength of CIV 1549 gives CIV 1549/CIII] 1909 0.2.

Fig. 2. The spectrum of the extended emission from the quasar PKS 0445+097. The spectrum was extracted from a region that spans from 1.4 arc seconds to 2.9 arc seconds from the nucleus of PKS 0445+097 and was specifically chosen to avoid the broad line emission from the nucleus.

3.2. The longslit spectrum of PKS 2338+042

The longslit spectrum of PKS 2338+042 reveals extended Ly emission. As described previously, we extracted the spatially-resolved Ly emission in 0.9" wide bins. In Fig. 3, we show a portion of the longslit spectrum specifically selected to show the region around Ly . As can be seen, the emission along PA= is strongly one-sided and with the most intense, most extended emission being on the side with the radio jet and most intense, most distorted radio emission (see Barthel et al. 1988 and Lehnert et al. 1997a). In Fig. 4, we show a spectrum of the sum of the extended emission from the southeastern and northwestern sides of the nucleus along the slit of PKS 2338+042. In Fig. 5, we show the velocity structure of the Ly emission. We see that the velocity offsets of the extended Ly emission relative to the nucleus of PKS 2338+042 are relatively small. We have chosen the wavelength of the absorption (4362.9Å) in the center of the Ly emission from the quasar as the zero-point for showing the velocity structure. The wavelength of the absorption corresponds to z=2.5888. Unfortunately, it is difficult to determine how the velocity of the Ly absorption compares with that of the emission since most of the observed lines are strongly affected by associated absorption. Only HeII has a profile that appears to be relatively unaffected by strong associated absorption and is relatively narrow (observed to be about 25Å). The observed wavelength of the nuclear HeII line implies a redshift of 2.5889, in close agreement with that of the associated Ly absorption. As can be seen the overall flux weighted average velocity of the extended emission line gas (represented by hollow squares in Fig. 4) is small - only being about 100 km s^-1 to the southeast and about 200 km s^-1 to the northwest. Although, we should note that some of the offsets are quite large in the very faint, most extended gas. About 6.3" to the southeast we measure a velocity offset of about 900 km s^-1.

Fig. 3. A section of the full 2-dimensional spectrum of PKS 2338+042 shown to highlight the Ly emission from both sources. The bottom spectrum is of the quasar, while that at the top shows the putative Ly emission from the object serendipitously placed along the slit. The x-axis axis is in angstroms and the y-axis is in pixels (0.22" pixel-1). The displayed portion of the long slit spectrum is approximately 240Å 40 arc seconds.

The extended Ly emission line is also very broad. Overall the extended Ly emission has line widths of 1300 km s^-1 to the southeast and about 1050 km s^-1 to the northwest. There is some tendency for the line widths to narrow with increasing angular distance from the nucleus. We also note in Fig. 5 the width of the nucleus Ly absorption (indicated by the point at zero radius). We can see that the absorption width is very narrow (only 500 km s^-1 FWHM) compared to the width of the extended emission line gas (about 1300 km s^-1). However, the measured width of the Ly absorption is probably best described as a lower limit. In making this measurement, we assumed that the continuum against which the absorption is taking place is accurately represented by the observed peaks in the Ly emission line profile. Undoubtably, the profile of the Ly line is still increasing at the point of the highest observed points of the line and thus the true amount of absorption is probably much higher than we have estimated.

Fig. 4a and b. The top spectrum is that off the extended emission from the quasar PKS 2338+042 on the southeastern side of the nucleus. The bottom spectrum is that extracted from the extended emission on the northwestern side of the nucleus along PA= . The two spectra were extracted over a region that was 1.6 arc seconds to 7.5 arc seconds on the southeastern side of the nucleus and 3.2 arc seconds to 6.7 arc seconds on the northwestern side of the nucleus. These regions were specifically chosen to avoid the obvious broad-line emission from the quasar nucleus. On the southeastern side of the nucleus, we identify to weak lines other than Ly ; CIV at 5565.3Å and HeII at 5880.7Å. On the northwestern side of the nucleus, we only identify weak CIV at 5567.9Å.

Fig. 5a and b. At the top, the spatially resolved velocity structure of the extended Ly emission from PKS 2338+042. The zero-point of the velocity scale was chosen to be the redshift of the strong Ly absorption line seen in the nuclear spectrum of PKS 2338+042. The redshift of the Ly absorption line is 2.5888, which corresponds quite closely to that of the nucleus HeII 1640 line (i.e., 2.5889). The bottom plot shows the spatially resolved line widths of the extended Ly emission from PKS 2338+042. The hollow squares in both plots represent the integrated measurements on each side of the nucleus as measured on the spectra shown in Fig. 4.

The individually extracted spectra that had significant Ly did not show significant emission from CIV 1549 or HeII 1640. However, in the sum of these spectra we do detect very weak (but significant) CIV 1549 and HeII 1640 emission on each side of the quasar nucleus along the slit. For the spectrum on the southeastern side of the nucleus, the line identified as CIV has a measured ratio of 0.06 relative to Ly (the night was not photometric), a central wavelength of 5565.3Å (corresponds to z=2.593), a width of 17.2Å, and is a 7 detection. For HeII we measure 0.03, a central wavelength of 5880.7Å (which corresponds to z=2.586), a width of 10.7Å, and the line is a 5 detection. For the northwestern side of the nucleus we find that CIV has a measured ratio of 0.15 relative to Ly , a central wavelength of 5567.9Å (corresponds to z=2.594), a width of 11.2Å, and is a 7 detection. We only measure an upper limit to the HeII emission on this side of the nucleus which implies 0.06.

In addition to seeing extended line emission from PKS 2338+042 we also see another object along the slit with a very strong line. This object lies 29.2" to the southeast of the nucleus of PKS 2338+042 along PA= . We show the extracted spectrum in Fig. 6. We find that the one obvious line has a wavelength of 4455.0 0.4Å, a measured width of 32.0 0.7Å and a total flux 1.3 10^-16 ergs cm^-2 s^-1. The line is also very broad (FWHM=2150 50 km s^-1) and has a high equivalent width (2100 100Å). We have also measured the break due the Ly forest if this line is identified as Ly . If we quantify the amount of continuum depression due to Ly absorption lines to the blue of the Ly using the definition of Schneider et al. 1991, namely =1- , where is the observed flux density at blueward of Ly and is the flux density of the extrapolated continuum blueward of Ly , we find that =0.26 for the unidentified object. This is very similar to that measured for the quasar, =0.19, which is in turn consistent with measurements of quasars at similarly high redshifts (see Schneider et al. 1991).

Fig. 6. The spectrum of the "companion" galaxy that was serendipitously placed along the slit.

© European Southern Observatory (ESO) 1998

Online publication: March 23, 1998
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