next previous
Up: Optical morphology of distant images


Subsections

3 Reduced images: Overview of the morphology

In this section we give a greyscale image and a contour map for each identified object (Fig. 3) The close environment and faint features can be studied from the greyscale image and the confidence level of the features and light distribution from the contour map. The field of view of the greyscale image is indicated in the upper left hand corner. The images are slightly smoothed with a Gaussian function ($FWHM=\frac{1}{2}~{\rm seeing}$) in order to enhance the low surface brightness features and maintain the resolution of the original images. The centre of gravity of the radio source and the positions of the radio lobes are indicated with a cross and circles, respectively. The images are presented in linear scale from 0$\sigma$ to 10$\sigma$ above the background of the image. In contour maps the object is in the origin and the numbers on both the vertical and horizontal axes refer to distance in arcsecond. The contour interval is 0.5 mag arcsec-2 and the surface brightness of the lowest contour is indicated in the upper right hand corner. The limiting surface brightness at which objects can be detected is typically between 25 and 26 mag arcsec-2. For RC 1510+0438 we also give V and I band images. Uncertain identifications are presented in Fig. 4 and "faint objects'' in Fig.  5.

The magnitudes are based on aperture photometry using DAOPHOT. The size of the aperture was selected in such a way that 1) as much light as possible was included in the aperture while keeping the errors reasonable but 2) the companions were excluded. The image shapes are determined by the moments of the brightness distribution using IMEXAMINE (Eq. (4) in Valdes et al. 1983) with the size of the aperture the same as in photometry. The estimation is vague for small ellipticity (e.g. RC 1152+0449) or when the inner regions have a different position angle than the outer regions (e.g. RC 1031+0443). The results of photometry and image shape analysis are given in Table 4. The magnitudes between this work and K95b are generally in agreement. The differences are primarily caused by the better seeing conditions at NOT, as compared with the 6 m-telescope and the different size of the aperture.

  
\begin{figure}
\includegraphics [height=21cm]{ds7556f3a.ps}\end{figure} \begin{figure}
\includegraphics [height=21cm]{ds7556f3b.ps}
\end{figure} \begin{figure}
\includegraphics [height=21cm]{ds7556f3c.ps}
\end{figure} Figure 3: Optical R-band images of identified RC/USS-sources. North is up and east is to the left. The size of the greyscale image is indicated in the upper left hand corner. The position of the radio lobes and centre of gravity are indicated by 1$\hbox{$^{\prime\prime}$}$ diameter circles and a cross, respectively. The contour image is a $20\hbox{$^{\prime\prime}$}\times20\hbox{$^{\prime\prime}$}$ field around the object. The surface brightness of the lowest contour is indicated in the upper right hand corner. The offset in arcseconds relative to the identified object is also indicated. In addition we give V- and I-band contour maps for RC 1510+0438 and V-band greyscale image for RC 1740+0502. See text for comments on each object

 
\begin{figure}
\includegraphics [height=21cm]{ds7556f3d.ps}
\end{figure} \begin{figure}
\includegraphics [height=21cm]{ds7556f3e.ps}
\end{figure} \begin{figure}
\includegraphics [height=23cm]{ds7556f3f.ps}
\end{figure} Figure 3: continued

  
\begin{figure}
\includegraphics [width=18cm,height=13.6cm]{ds7556f4.ps}\end{figure} Figure 4: Grey scale images of all the uncertain identifications (see Sect. 3.2). The images are produced in the same way as for Fig.  3. For RC 0459+0456 we also give an R-band contour map
  
\begin{figure}
\includegraphics [height=13.6cm]{ds7556f5.ps}\end{figure} Figure 5: Grey scale images of the faint objects (see Sect. 3.3)

3.1 Identified objects

In this section we give notes on individual objects (Fig.  3). For the strongest sources alternative names are given in brackets.


RC 0457+0452
This is one of the brightest objects in this sample. The new VLA map shows that the radio source has FRI structure (an unpublished radio map). This agrees with a high optical to radio luminosity ratio (Parijskij et al. 1996a). There is a near companion $\sim$2.5$\hbox{$^{\prime\prime}$}$ northwest from the nucleus. In addition there are four faint companions in the southeast (5$\hbox{$^{\prime\prime}$}$). The position angle of the galaxy is not uniform, which is possibly due the close companions. The inner isophotes are roughly perpendicular to the radio axis and the outermost fuzz is roughly aligned with the radio axis. The same trend can be seen in both R and V-band images. This object is possibly situated in a cluster of galaxies and there are a few companions with similar brightness. The companion 20$\hbox{$^{\prime\prime}$}$ to the east has a double nucleus (mR=19.26, mV-R=0.69), hence it is apparently a merger, and the companion 22$\hbox{$^{\prime\prime}$}$ to the south has distorted morphology (mR=19.94, mV-R=0.93).


RC 0506+0508
This is a faint point-like source, even under excellent seeing conditions. It might be a high redshift (z>1, mR< -23) quasar because in the quasar catalogue by Veron-Cetty & Veron (1996) there are only a few quasars fainter than 21 magnitudes with z<1. The companions 14$\hbox{$^{\prime\prime}$}$ to the northwest have a multicomponent structure with an extended diffuse emission.


RC 0837+0446
The galaxy is marginally resolved and lies in or behind a galaxy cluster. In the lower left hand corner of the grey scale image is a trail of a solar system object.


RC 0845+0444
The optical counterpart of this radio source coincides with the western radio component. This object is optically extended and there is a faint extension towards the southwest.


RC 1031+0443
(4C+05.43 & PKSB1028+049). The galaxy is near the centre of gravity of the radio source. The object is extended and has a multicomponent structure. The strongest optical emission is aligned with the radio source, but the position angle of the outermost isophotes is almost perpendicular to the radio axis.


RC 1152+0449
This galaxy has two or possibly three components. The outer isophotes of the galaxy are box-like, but the separate components are roughly aligned with the radio axis. The faint companion 4$\hbox{$^{\prime\prime}$}$ to the west is near to the western radio lobe. This blue companion may be related to the radio source ($m_{R}=23.0, m_{V-R}\sim~0.3$).

This is the only source where the astrometry of the present work is not consistent with the result of K95b, but coincides with current identification in Parijskij et al. (1996a).


RC 1155+0444
This is the brightest galaxy in our sample. The galaxy is elliptical and it is clearly aligned with the radio source. The two neighbouring galaxies are possibly interacting foreground galaxies.


RC 1235+0453
This faint galaxy is spatially extended in our R-band images. The fuzz $\sim$1$\hbox{$^{\prime\prime}$}$ northwest from the nucleus has a clumpy structure. Our deep images show faint low surface brightness companions near the object $\sim 10 \hbox{$^{\prime\prime}$}$ to the east, north and west. In the V-band images only the core of the galaxy is detected.


RC 1347+0441
This galaxy is the faintest of our sample. The object is elongated and the size of the optical object is roughly the same as the radio source.


RC 1510+0438
This is the most spectacular object in our sample, lying in a group of galaxies and having apparently wavelength dependent properties. In the R- and I-band image the object is almost round (Table 4) but in the V-band the object is weakly elongated with the same position angle as the radio source. The redshift estimation from BVRI colours suggest $z\sim0.6$ (Pariskij et al. 1996b). If this is the case, the strong emission lines [Oii] 3727 and [Oiii] 5007 would be shifted into R and I band, respectively, possibly causing the wavelength dependence of morphology. However, new colours from the 6 m-telescope do not agree with strong line contribution. Another consequence of such redshift would be that this would be one of the faintest (intrinsically) radio galaxies in the Hubble diagram (Fig.  2). There are three relatively bright galaxies and one faint companion galaxy within 5$\hbox{$^{\prime\prime}$}$ of the object. All the companions are bluer than the object (mR-I=1.52). The objects towards the east, C1 (mR=22.54, mV-R=0.51, mR-I=0.27), north, C2 (mR=22.34, mV-R=0.81, mR-I=0.87) and west,C3 (mR=23.24, mR-I=0.83) could be foreground galaxies. In addition there is a faint companion 1$\hbox{$.\!\!^{\prime\prime}$}$5 north from the object.


RC 1703+0502
(PKS B1701+051). This is one of the strongest and most compact radio sources of the present sample. The optical and radio axes are clearly aligned and the sizes are almost the same. There are a few faint galaxies in the field, but no close companions. This object is possibly located behind a foreground galaxy cluster although some of the field objects might be faint galactic stars.


RC 1720+0455
This object is compact in radio and optical. This suggests that it is a QSO and the same conclusion may be drawn from radio-optical luminosity consideration (Parijskij et al. 1996a). The extension towards the southeast, seen in K95b, was an artifact. There are a few companions close to the object. The southern companion either has a double nucleus or a dust lane. The wide field image shows several faint companions, hence this galaxy is either in a cluster of galaxies or behind one.


RC 1740+0502
This source was identified by K95b and it is marginally resolved in the R-band image. In the V-band image the object has an extension to the south west in contrast to almost round morphology in R-band (see Table 4).


RC 2013+0508
This unresolved object could possibly be a quasar. Because of its low galactic latitude ($b\sim-15$), the field is crowded with stars.


RC 2036+0451
(MRC 2034+046). This is the second of the two triple radio sources in this sample. A point source coincides with the central component fairly well. This is the only object with known redshift (z=2.95 Pariskij et al. 1996a). This indicates that the absolute magnitude of this quasar is $m_R\approx-29$.


RC 2144+0513
This object is unresolved. The companion 3$\hbox{$^{\prime\prime}$}$ to the southwest is most likely a galactic star (mR=20.90, mV-R=1.1). The profile of this object matches perfectly with the average stellar profile from the same field.

3.2 Uncertain identifications

RC 0459+0456
(MRC 0456+048) This source has two candidates for optical identification in K95b. Id1 (mR=22.08) is an elongated galaxy with roughly the same position angle as the radio source. This object has a companion to the west (Id2). This is a marginally resolved point-like source, hence it might be a quasar with a host galaxy (mR=21.12). FWHM of the id2 0$\hbox{$.\!\!^{\prime\prime}$}$66 compares with FWHM of a field star 0$\hbox{$.\!\!^{\prime\prime}$}$62.


RC 1219+0446
This is the largest radio source in our sample (118$\hbox{$^{\prime\prime}$}$). The nature of the source remains unclear and it is possible that there are indeed two independent radio sources. If this is one source, then a possible identification would be a faint, rather round galaxy (Id1) 5$\hbox{$^{\prime\prime}$}$ from the centre of radio source (mR=21.9). On the other hand if the southern radio lobe is an independent object, the identification could be an unresolved object (Id2) 2$\hbox{$^{\prime\prime}$}$ southeast from the radio source (mR=17.88).


RC 1735+0454
The possible optical counterpart is $\sim$3$\hbox{$^{\prime\prime}$}$ to the east of the radio source. The galaxy has several components and it is elongated in a north south direction. The identification should be confirmed by future observations.

3.3 Faint objects

RC 0743+0455
This object is very faint and hardly visible in the 30 min exposure.


RC 1333+0451
The radio source is compact. There is a faint extended emission exactly at the position of the radio source.


RC 1609+0456
New 6-m telescope measurements find an object with $m_{R}\sim25.5$ exactly at the position of the radio source. Our 600 s exposures are not deep enough to detect this object. The bright nearby object is unresolved and BVRI photometry by K95b suggests it to be a star.


next previous
Up: Optical morphology of distant images

Copyright The European Southern Observatory (ESO)