3 Comments on individual objects

  
3.1 PKS 1302-102

Figure 1: Images of PKS 1302-102 in the H-band. The top-left panel and bottom panel correspond to the image, respectively, before and after deconvolution. The spatial resolutions are respectively FWHM $\sim$ 0.32  and 0.24 arcsec. The top right panel shows the two companions after substraction of the PSF and a model for the host-galaxy. The inset in the bottom panel corresponds to a higher contrast version of the inner 4 arcsec $\times$4 arcsec

The image obtained at CFHT under moderately good seeing conditions is of similar quality to that obtained with HST by Bahcall et al. (1995) (see for comparison Hutchings et al. 1994) with FWHM = 0.24 arcsec after deconvolution (see Fig. 1). The two objects at 1 and 2 arcsec from the quasar are well-detached, and are more clearly seen when both the PSF and a model for the host-galaxy (obtained by masking the companions and fitting ellipses to the isophotes) are subtracted. It is unlikely that these companions are intervening objects as strong associated metal line absorption would be expected at such a small impact parameter when no such absorption is detected in the HST spectrum down to $w_{\rm obs}$ $\sim$ 0.2 Å  (Jannuzi et al. 1998). The host-galaxy of this quasar has been detected by HST and fitted with a r^1/4 profile (Boyce et al. Disney et al. 1995). Márquez et al. (1999) derive that the galaxy contributes 40% the total flux in the J-band when McLeod & Rieke (1994) measure this contribution to be 31% of the total flux in the H-band after fitting an exponential profile to the host-galaxy. We have performed a similar fit on the present data and found that the contribution of the galaxy amounts to 39% in H and 18% in K (see Table 2). However, Fig. 4 shows that an r^1/4 profile is a better fit. In that case, the contribution of the host-galaxy to the total light is 70% (60%) in H (K), in good agreement with the values derived by subtracting a scaled version of the PSF and directly integrating the residual flux.

  
3.2 PG 1700+514

Figure 2: Images of PG 1700+514 after deconvolution using the PSF given by three stars observed during the same night. The best deconvolution is obtained using the star with the FWHM closest to that of the quasar. The resulting image (bottom) has a final resolution of FWHM = 0.16 arcsec

PG 1700+514 is one of the most infrared-luminous, radio-quiet BAL quasars (Turnshek et al. 1985; Turnshek et al. 1997). Ground-based imaging revealed an extension about 2 arcsec north-east of the quasar (Stickel et al. 1995) which was shown by adaptive-optics imaging and follow-up spectroscopy to be a companion with a redshift 140 km s^-1 blueward of the quasar (Stockton et al. 1998). NICMOS observations lead Hines et al. (1999) to argue that the companion is a collisionally induced ring galaxy. The fit to the SED and the Keck spectrum of the companion imply that the light is emitted by an old population of stars plus a 85 Myr old star-burst (Canalizo & Stockton 1997). Note however that the H-band flux (m_H $\sim$ 16.6) deduced from HST imaging is much larger than that predicted by the model. Stockton et al. (1998) showed that the inclusion of embedded dust can produce a spectral-energy distribution that is consistent with both the optical spectrophotometry and the IR photometry.

The image obtained at CFHT is shown in Fig. 2. We confirm the findings by Stockton et al. (1998) that the companion has the appearance of an arc with several condensations. We used different PSF to deconvolve the image. The best deconvolution is obtained using the star with the FWHM closest to that of the AGN (0.30 arcsec, see Sect. 2). The image has a final resolution of 0.16 arcsec and is probably the best image obtained yet on this object. The companion is seen as a highly disturbed system with a bright nucleus and a ring-like structure; the nucleus being decentered with respect to the ring. The host-galaxy is clearly seen around the quasar with a bright extension to the south-west, first noted by Stickel et al. (1995) and clearly visible in the optical images by Stockton et al. (1998). In addition, we detect a bright knot to the south-east which is not seen in the NICMOS data probably because of the presence of residuals in the PSF subtraction. The comparison between the HST and CFHT images of PG 1700+514 shows how powerful AO can be, and bodes well for the use of the technique on 10 m-class telescopes. No obvious relation is found between the near-IR image and the radio map (Hutchings et al. 1992).

  
3.3 Other objects

3C 232 - TON 0469 This object has attracted much interest because it is located 2 arcmin ($\sim$8h^-1 kpc at z = 0.0049) north of the nearby (z = 0.0049) galaxy NGC 3067 and has been considered as the prototype of the galaxy-quasar physical association as a probe for anomalous redshifts (Hoyle & Burbidge 1996). The HST spectrum shows a strong Mg  II system at $z_{\rm abs}$ = 0.0049 (Tumlinson et al. 1999) which has been shown to be due to an H  I tidal tail originating in the disk of the foreground galaxy (Carilli et al. 1989). The MERLIN map at 1.6 GHz shows a slight extension to the east (Akujor et al. 1994). The host-galaxy is detected in the CFHT image with an extension to the south-west up to 5 arcsec from the quasar). From both the image (Fig. 3) and the profile fitting (Fig. 4) we derive that the host is better described as an elliptical galaxy.

PG 1001+291 - Ton 0028 Only one image from the HST archive has been published yet (Boyce et al. 1999). These authors favor the interpretation that the object is an interacting object with two nuclei, one 1.9 arcsec to the south-west and the other 2.3 arcsec to the north-east. We find no evidence for the presence of two nuclei. In particular there is no residual after subtraction of a host-galaxy model. The profile is not well fitted by a single disk component, due to the presence of a bump which is characteristic of the bar component in the profiles of barred spirals. We therefore conclude that the elongated NE-SW feature seen in our image probably reveals the presence of a strong bar in an otherwise spiral galaxy.

PG 1012+008 This radio-quiet quasar interacts with two companions located to the north and east (Heckman et al. 1984). It has been imaged with HST by Bahcall et al. (1997) who concluded from 2D-modelling that the host is a spiral galaxy with r_1/2 = 10.8 kpc. They also fit the one-dimensional profile as an elliptical with r_1/2 = 24.5 kpc. The best 2D fit by McLure et al. (1999) is a large elliptical with r_1/2 = 23 kpc. We find that the best fit to the H-band profile is a r^1/4 law with a scalelength of 2.9 arcsec or 6h^-1 kpc (see Fig. 3).

PG 1402+261 - TON 0182 Bahcall et al. (1997) determined from HST imaging that the host of this quasar is a bright spiral galaxy with prominent H  II regions located along the spiral arms. The CFHT image shows that there is a bright elongation extending $\sim$2 arcsec away from the nucleus on both sides of it in the NW-SE direction, probably tracing a strong bar also seen as a bump in the surface brightness profile, see Fig. 4.

B2 1425+26 - TON 0202 This quasar is hosted by a bright galaxy probably in mild interaction with one of the three companions located within 10 arcsec from the point source and listed by Hutchings et al. (1984) and Block & Stockton (1991). Two of these companions are detected in our H and K-band images. The host-galaxy has been classified as elliptical by previous investigators (Malkan 1984; Kirkhakos et al. 1999). However, the isophotes in our image are distorted and an arc-like feature is clearly seen to the west (see also the F555W image of 1999). Moreover, an emission line nebulosity is detected by H$\alpha$, H$\beta$, [O  III] emission up to 3 arcsec from the nucleus (Boroson et al. 1984; Stockton & MacKenty 1987). Our fit shows that an elliptical galaxy (or an early spiral) is a good description for the host-galaxy (see Fig. 4).

3C 334 The host-galaxy has twisted isophotes. As noted by Lehnert et al. (1999), the galaxy appears elongated approximatively in the same direction as the radio structure (Hutchings et al. 1998). Note that the arc-like structure seen to the south in the deconvolved image was detected by its [OII] emission (Hes et al. 1996). Comparison of the new AO corrected images with previous ground-based images (e.g. Hes et al. 1996; Márquez et al. 1999) clearly shows the power of AO technique. We note that three Lyman-$\alpha$ absorptions are detected in the quasar spectrum with $w_{\rm obs}$ = 0.37, 1.00 and 0.21 Å  at redshifts $z_{\rm abs}$ = 0.5387, 0.5449 and 0.5491, slightly smaller than the emission redshift $z_{\rm em}$ = 0.555 (Jannuzi et al. 1998). Spectroscopy of the companions is required to determine if they are somehow associated with these absorption systems. The profile fitting does not allow us to distinguish between a disk-like or an elliptical host.

3C 351 We observed this field in the H and K-bands (see Fig. 3). The two objects closest to the line of sight in our image are situated 7 arcsec north-east of the quasar. One is a bright spiral galaxy, well resolved in our images, the other is very faint (it is barely visible in Fig. 3 but it is more clearly seen in the deconvolved image) and could be a companion of the former. Lanzetta et al. (1995) and Le Brun et al. (1996) have searched the field around 3C 351 for galaxies responsible for Lyman-$\alpha$and C  IV absorption observed by Bahcall et al. (1993) in the HST spectrum of the quasar. There are two Lyman-$\alpha$ absorption lines at $z_{\rm abs}$ = 0.2216 and 0.2229, the former showing C  IV absorption as well. Le Brun et al. (1996) identified the metal line system with a galaxy 710 h^-1₅₀ kpc away from the line of sight. The redshift of the two objects closest to the quasar have not been determined however and it is possible that these two objects are responsible for the absorptions. If they are at z = 0.222, the impact parameter is of the order of only 15h^-1 kpc. It is very important to confirm this for our understanding of the nature of H  I halos around low-z galaxies. Boyce et al. (1998) detect a companion at about 3.3 arcsec east to the quasar. We do not detect this companion in any of our images although it is within the possibilities of our imaging. This may indicate that the flux in the HST-F702W filter is dominated by line emission or that the object is very blue. As there is no strong intervening absorption in the spectrum of the quasar, it is probable that this companion is at the redshift of the quasar. Note that 3C 351 exhibits a strong associated system with H  I Lyman-$\alpha$, C  IV, N  V and O  VI absorptions. The presence of the associated system does not seem to be related to any other imaging property of the QSO.

B2 1721+34 The host-galaxy is detected up to 1.5 arcsec from the central point-source in the H-band CFHT image (see Fig. 3). The one-dimensional profile shows that a r^1/4law fits the galaxy profile better than an exponential fit, but images with better S/N ratio are needed to confirm this at higher significance.

Figure 3: Images of objects described in Sect. 3.3 and Tables 1 and 2. They are K band images for PKS 1302-102 and PKS 2128-12 and H band images for the rest. The scale is marked with the horizontal bar in the top-left figure and is the same for all the figures

PG 2112+059 Two companions are detected within 10 arcsec of the nucleus. An elliptical profile better describes the light distribution of the host-galaxy.

PKS 2128-12 Disney et al. (1995) fitted the one dimensional profile with a de Vaucouleurs law of radius $R_{\rm e}$ = 37.4 kpc. The images of this object have the poorest resolution in our sample. We are therefore unable to determine a reliable fit to the host-galaxy profile. We detect a companion at 7 arcsec north-east of the nucleus.

Figure 4: Top: surface brightness profiles (dots and error bars) obtained with the undeconvolved images in the H-band (except for PKS 2128-12, for which we used the K-band image because of its better PSF). Fits by a disk (dashed line) and a r1/4 law (dotted-dashed line) are overplotted. Bottom: residuals from the disk (stars) and r1/4 (crosses) fits in percentage. The vertical lines are drawn at respectively two and three times the PSF FWHM

Figure 5: Illustrative examples of mocked images and their fits. The top panel is the surface brightness profiles with models overplotted (exponential disk as a solid line and r1/4 law as a dashed line). a) The input is a disk galaxy and the mocked image is better fitted by a disk host (the quasar contributes 25% to the total light). b) The input is a disk galaxy but the mocked image is equally well fitted by the two laws. The disk parameters are the same as is a), but the quasar contributes 70% to the total light. c) When the input is an elliptical galaxy, the mocked image is always better fitted by a r1/4 profile