A&A 374, 861-870 (2001)
DOI: 10.1051/0004-6361:20010746

A new sample of giant radio galaxies from the WENSS survey

I. Sample definition, selection effects and first results [*],[*]

A. P. Schoenmakers1,2,3,[*] - A. G. de Bruyn3,4 - H. J. A. Röttgering2 - H. van der Laan1


1 - Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
2 - Sterrewacht Leiden, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
3 - ASTRON, PO Box 2, 7990 AA Dwingeloo, The Netherlands
4 - Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands

Received 22 August 2000 / Accepted 23 May 2001

Abstract
We have used the Westerbork Northern Sky Survey (WENSS) to define a sample of 47 low redshift ( $z \mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil $\displaystyle ...) giant radio galaxies. This is the largest sample yet of such radio sources originating from a single survey. We present radio maps of the newly discovered giants and optical images and spectra of their host galaxies. We present some of their properties and discuss the selection effects. We investigate the distribution of the sources in the radio power - linear size P-D diagram, and how these parameters relate to the redshifts of the sources in our sample. We find a strong drop in the number of sources with a linear size above 2 Mpc. We argue that this is not a result of selection effects, but that it indicates either a strong luminosity evolution of radio sources of such a size, or that a large fraction of radio sources "switch off'' before they are able to grow to a size of 2 Mpc.

Key words: galaxies: active - intergalactic medium - galaxies: jets - radio continuum: galaxies


1 Introduction

The central activity in a fraction of Active Galactic Nuclei (AGN) is capable of producing relativistic outflows of matter, the so-called "jets'', for a prolonged period of time, possibly up to a few 108 yr. These jets, when powerful enough, inflate a cocoon (e.g. Scheuer 1974; Falle 1991) which expands first in the Interstellar Medium (ISM) and later in the Intergalactic Medium (IGM) of the host galaxy. The evolution of such cocoons is traced by the radio lobes, which in themselves are only a (albeit important) "side effect'' caused by the presence of magnetic fields in the cocoon.

The giant radio galaxies (GRGs) are those radio sources whose lobes span a (projected) distance of above 1 Mpc[*]. As such, GRGs must represent a late phase in the evolution of radio sources. Models of radio source evolution (e.g. Kaiser et al. 1997; Blundell et al. 1999) predict the radio power and linear size evolution of powerful radio sources with time. According to these models, GRGs must be extremely old (i.e. typically older than 108 yr) and probably also located in underdense environments, as compared to smaller radio sources of comparable radio power (e.g. Kaiser & Alexander 1999).

Multi-frequency radio observations (Mack et al. 1998) have shown that spectral ages of GRGs are of the same order as expected from source evolution models. It is, however, not clear at all whether spectral ages are representative of the dynamical ages (e.g. Parma et al. 1999). This questions the validity of radio-based determinations of the properties of the environments of these sources. Still, constraints on the environments of GRGs are of high importance since the radio lobes of these sources penetrate deeply into the intergalactic medium. It is almost impossible to find the properties of this medium, otherwise than from studies of such radio lobes (e.g. Subrahmanyan & Saripalli 1993).

A major problem for such studies is that currently known GRGs have not been uniformly selected. The difficulties encountered while selecting extended radio sources have been demonstrated by Saunders et al. (1987), who have searched for GRGs in a small region of the 151-MHz 6C survey. The 6C survey, with only 30 mJy beam-1 RMS-noise and a beamsize of $4.2\hbox{$^\prime$ }\times4.2\hbox{$^\prime$ }\,{\rm cosec}\,\delta$ FWHM (with $\delta$ the declination) has an excellent sensitivity to large, faint objects. However, using higher resolution observations they found that only at integrated flux densities above 5 Jy has a radio source larger than $5\hbox {$^\prime $ }$ a good chance of being a genuine GRG in the 6C. At a flux density level of 1 Jy, Saunders et al. find that most of the sources which appear as large extended structures on the 6C survey maps are the result of confusion of physically unrelated sources. Their work demonstrates that 1) an efficient search for GRGs has to be done with sufficient angular resolution to minimize confusion problems and that 2) it should be done with a high sensitivity, also for large-scale structures (up to a few tens of arcmin) on the sky. The recently completed WENSS survey (Rengelink et al. 1997) meets both these demands.

In this paper we report of the selection of new giant radio sources from the WENSS. Subsequent papers will present additional radio observations (Schoenmakers et al. 2000b), a more detailed analysis of the spectroscopic data and a discussion of the evolution of GRGs (in preparation, but see Schoenmakers 1999a). In Sect. 2 we outline the selection technique and criteria. Section 2.5 presents the strategy we have adopted for finding the optical identifications, and Sect. 3 describes the spectroscopic observations of these identifications. In Sect. 4 we present the first results of the new sample of GRGs: Flux densities, linear sizes, redshifts, etc. A discussion of these results and on the sensitivity of the WENSS survey to extended radio sources is given in Sect. 5.

Throughout this paper, a spectral index $\alpha$ is defined according to the relation $S_{\nu} \propto \nu^{\alpha}$ between flux density $S_{\nu}$ at frequency $\nu$, and the frequency $\nu$.

  
Table 1: List of all previously known GRGs (i.e. before 1998) in the area of the sky covered by the WENSS and fulfilling our selection criteria. Column 1 gives the name of the source in IAU-format; Col. 2 gives the more common name of the source, if available; Cols. 3 and 4 give the coordinates of the host galaxy in B1950.0; Cols. 5 and 6 give the redshift of the host galaxy and a reference to it; Col. 7 gives the projected linear size of the radio source in Mpc; Col. 8 designate the morphological type of the radio source, i.e. FRI or FRII or an intermediate type, FRI/II. If a "B'' is added, it means that the host galaxy is a broad-line object, a "Q'' means that it is a quasar. Column 9 gives a reference to radio maps in which the radio morphology can be studied. Columns 10 and 11 give the flux density at 325 MHz and the reference for this value.


\begin{displaymath}\begin{tabular}{l l l l l l c l l r@{$\,\pm\,$}r l} \hline\h... ... & R88 & 4.76 $\pm$ 0.10 & WE \\ \hline \hline % \end{tabular}\end{displaymath}


References: B72: Burbidge & Strittmattar (1972); B81: van Breugel & Willis (1981); B82: van Breugel & Jägers (1982); B89: de Bruyn (1989); C75: Colla et al. (1975); D70: Demoulin (1970); D90: Djorgovski et al. (1990); DJ95: Djorgovski et al. (1995); FB78: Fomalont & Bridle (1978); G92: de Grijp et al. (1992); H79: Hine (1979); J86: Jägers (1986); M79: Miley & Osterbrock (1979); MA79: Masson (1979); M96: Marcha et al. (1996); M97: Mack et al. (1997); P84: Perley et al. (1984); P96: Parma et al. (1996); R88: Riley et al. (1988); R96: Röttgering et al. (1996); S73: Sargent (1973); S80: Strom & Willis (1980); S81: Strom et al. (1981); S82: Saunders (1982); S83: Strom et al. (1983); S85: Spinrad et al. (1985); S86: Saripalli et al. (1986); S87: Saunders et al. (1987); S97: Simien & Prugniel (1997); V89: Vigotti et al. (1989); WE : WENSS (measured in the radio map); W74: Willis et al. (1974); W77: Wagett et al. (1977); W81: Willis et al. (1981).


   
2 Sample selection

2.1 The WENSS survey

The Westerbork Northern Sky Survey is a 325-MHz survey of the sky above $+28\hbox{$^\circ$ }$ declination. About a quarter of this area has also been observed at a frequency of 609 MHz. The unique aspect of WENSS is that it is sensitive to spatial structures over 1 degree on the sky at 325 MHz. The limiting flux density to unresolved sources is about 15 mJy ($5\sigma$) and the FWHM of the beam is $54\hbox{$^{\prime\prime}$ }\times 54\hbox{$^{\prime\prime}$ }{\rm cosec}\,\delta$, with $\delta$ the declination. A detailed description of the observing and data reduction techniques used can be found in Rengelink et al. (1997). The sky area above $+74^{\circ}$ declination has been observed with an increased total bandwidth, so that the limiting flux density to unresolved sources is about 10 mJy ($5\sigma$) in this sky area.

Using the Wieringa (1991) source counts at 325-MHz, the flux density at which the same amount of confusion in the WENSS as Saunders et al. (1987) encountered in the 6C survey can be calculated. For a typical radio source spectral index of -0.8, a similar amount of confusion can be expected in the WENSS at a flux density of ${\sim}400$ mJy, which is almost seven times lower than that for the 6C survey. Similarly, it can be shown that confusion would dominate the selection sources only below 20 mJy in the WENSS survey, which is below its completeness limit of ${\sim} 30$ mJy (Rengelink et al. 1997). This implies that we should be able to efficiently find GRGs in the WENSS down to relatively low flux density levels.

2.2 Selection criteria

In order for a source to be a candidate low redshift GRG, we have used the following criteria. A candidate GRG must have:

1.
an angular size larger than 5 arcminute, and
2.
a distance to the galactic plane of more than 12.5 degree.
The angular size lower limit of $5\hbox {$^\prime $ }$ is the size at which some basic morphlogical information of a source can still be obtained at all declinations the survey has covered. this corresponds to a physical size of ${\sim}750$ kpc at z=0.1, ${\sim}1300$ kpc at z=0.2 and ${\sim}1700$ kpc at z=0.3, and will therefore introduce a redshift-dependent linear size bias in the sample. To avoid high galactic extinction values and confusion by a large surface density of foreground stars, we have restricted ourselves to galactic latitudes above $12.5\hbox{$^\circ$ }$. This results in a survey area of ${\sim}2.458$ steradian ( ${\sim}8100^{\ifmmode\hbox{\rlap{$\sqcap$ }$\sqcup$ }\else{\unskip\nobreak\hfil ... ...{\rlap{$\sqcap$ }$\sqcup$ } \parfillskip=0pt\finalhyphendemerits=0\endgraf}\fi}$).

Table 1 presents all previously discovered GRGs whose angular size and position on the sky agree with the above selection criteria. The majority of these are smaller than 2 Mpc in size. If their sizes are characteristic for the whole population of GRGs, we thus expect that the majority of selected sources will have a redshift below ${\sim}0.35$. Assuming that the host galaxies are not less luminous than those of the LRL sample of powerful radio sources (Laing et al. 1983) they should be identifiable on the Digitized POSS-I survey (DSS).

2.3 Selection method

Candidate radio sources were selected using a visual inspection of the WENSS radio maps. We preferred this method over possibly more objective, machine controlled selection methods because the complexity of the WENSS radio maps (i.e. the high source surface density and the unavoidable presence of spurious artefacts such as low-level sidelobes of bright sources, etc.) and the wide variety in possible morphologies would make it very difficult to tune such an algorithm. Looking at the maps allows one to easily recognize low-level extended structures in a crowded field.

Above declination $+74\hbox{$^\circ$ }$ we have initially selected our candidates using the earlier available NVSS survey maps (Condon et al. 1998), but we subsequently repeated the selection using the WENSS maps. We found that no WENSS selected candidates were omitted using the NVSS. On the contrary, we have identified two NVSS sources (B1044+745 and B0935+743) that we most likely would not have selected from the WENSS survey alone due to their faintness in the latter. We will elaborate on this when we discuss the selection effects (Sect. 5.1).

2.4 Removing confused sources

The declination dependent beam size results in an unavoidable increase of confusion with decreasing declination. Only with higher angular resolution observations can we determine whether such sources are separate unrelated radio sources. We have used the following additional sources of radio data to achieve this:

First, where available, we have used the 612-MHz WENSS maps which have twice the resolution of the 325-MHz maps. Also the 1.4-GHz NVSS survey, which does not have a declination-dependent beam size and which covers almost the entire area of the WENSS survey, is highly usefull in this respect. Furthermore, we have used the much higher resolution ( $5\hbox{$.\!\!^{\prime\prime}$ }4$ FWHM) maps from the 1.4-GHz FIRST survey (Becker et al. 1995) where available. Also the FIRST survey has mapped a large fraction of the area observed by WENSS, notably the lower declination range away from the galactic plane. Finally, for candidates in areas of the sky where the FIRST survey was not (yet) available, we obtained short 1.4-GHz WSRT observations.

A consequence of the different methods used to eliminate confused sources is that the angular size of the objects are not well determined in all cases. There are two important factors which influence such estimates: First, for edge-brightened sources (FRII-type) high-resolution observations would be required for an accurate measurement, but we do not have these for all such sources and even the ones we have differ in quality and resolution. Second, for FR-I type sources the angular size measured on a map depends strongly on surface-brightness sensitivity. Therefore, sources may have been accidentally removed from the sample because of wrongly estimated sizes.

   
2.5 Identification of the host galaxies

We have used the digitized POSS-I survey (the "Digitized Sky Survey'', DSS) and, in a later stage, also the digitized POSS-II survey to identify the host galaxies of the selected radio sources. The magnitude limit of the red POSS-I plates is ${\sim}20{-}20.5$; the POSS-II is somewhat more sensitive.

Adopting the Cousin R-band magnitude-redshift relation for the host galaxies of the radio sources in the LRL sample (Dingley 1990), we expect to be able to identify host galaxies out to $z\sim 0.5$ (note that the transmission curves of the Cousin R-band and the POSS-E band are much alike).

To identify the host galaxy of a radio source which extends over several arcminutes, a radio core position is often necessary. We have used the WENSS, NVSS, FIRST and our own WSRT radio observations to identify radio cores of the selected sources. For many sources we indeed find a compact central radio source coincident with an optical galaxy in the POSS-I and/or POSS-II.

We cannot rule out that for an individual source the so-found optical galaxy is an unrelated foreground galaxy, and that the actual host galaxy of the radio source is a much farther and fainter galaxy. However, for the sample as a whole, we believe this to be only a minor problem: It would make the radio sources even larger than they already are and the chance of such an occurrence is very small anyway.

For the source B1918+516 the POSS-I plates did not show an obvious host galaxy candidate. Therefore, an optical CCD image has been made by P.N. Best using the LDSS imaging spectrograph on the 4.2-m WHT telescope on La Palma. This image (see Fig. .28) reveals a faint galaxy, close to a relatively bright star. We believe this galaxy to be the host galaxy, due to its proximity to the radio core.

We cross-correlated the positions of the optical galaxies with the NASA Extragalactic Database (NED). In case an optical source with known redshift is found and the resulting size of the radio source is below 1 Mpc, we removed that source from our sample. We present the list of remaining (i.e. after removing sources identified as non-GRGs on basis of NED data) candidate GRG sources in Table. .1. We provide IAU-formatted source names, approximate coordinates of the radio sources, WENSS flux densities, approximate angular sizes and whether we are convinced this a genuine giant radio galaxy candidate on basis of its radio morphology. We remark that many of the WENSS selected sources were rejected after a look at the maps of these sources from the NVSS survey.

   
3 Optical spectroscopy

Optical spectra of a large fraction of possible host galaxy of the candidates have been obtained. In order to construct an as complete as possible flux-density limited sample from our candidates, we have tried to obtain spectra and redshifts for all candidate sources in Table .1 with a 325-MHz flux density above 1 Jy[*]. In Table .2 we present the log of the spectroscopic observations. On the 2.5-m INT telescope on La Palma we used the IDS-235 camera with the Ag-Red collimator and the R300V grating. The camera was equipped with a 1k$\times$1k TEK chip. This setup results in a total wavelength coverage of ${\sim}3500$ Å and a pixel scale of ${\sim}3.2$Å/pixel in the dispersion direction and $0\hbox{$.\!\!^{\prime\prime}$ }74$/pixel in the spatial direction. Depending on the magnitude estimated redshift of the host galaxy candidate, the central wavelength of the spectrograph was set at either 5500, 6000 or 6500 Å. The slit-width was held constant at $2\hbox{$^{\prime\prime}$ }$. Only in the case of the source B0809+454 we used a $3\hbox{$^{\prime\prime}$ }$-wide slit because of uncertainties in the optical position at the time of observation. Flat-field observations were made at the beginning of each night by using the internal Tungsten lamp. Wavelength calibration was achieved by internal arc-lamp exposures (from CU-AR and CU-NE lamps) which were taken at the beginning of each night and immediately after each object exposure. For absolute flux calibration and to correct for the wavelength-dependent sensitivity of the instrument, several spectroscopical standard stars were observed each night, using a $5\hbox{$^{\prime\prime}$ }$-wide slit.

The spectra have been reduced using the NOAO IRAF data reduction software. One dimensional spectra have been extracted using a $4\hbox{$^{\prime\prime}$ }$-wide aperture centered on the peak of the spatial profile of the identification. The resulting spectra are shown in Figs. .1-.29. For each object exposure the wavelength calibration has been checked against several bright sky-lines in a non background-subtracted frame.

In addition to these observations, a spectrum of the source B1450+333 was obtained on 8 July 1997 by P.N. Best, using the 4.2-m WHT on La Palma, equipped with the ISIS spectrograph. An optical CCD image and a spectrum of the source B1543+845 were obtained by I.M. Gioia on 4 and 5 March 1998 using the HARIS imaging spectrograph on the 2.2-m University of Hawaii Telescope on Mauna Kea, Hawaii.

Table .5 presents the measured redshifts and the spectral features used to determine these. The optical images and spectra of the observed host galaxies are presented in Figs. .1-.29. For the source B1245+676 a high-quality spectrum and the therefrom derived redshift had been published earlier by Marcha et al. (1996). We have therefore not observed the host galaxy of this radio source again. We have, however, reobserved the source B1310+451 in order to obtain a higher quality spectrum of the host galaxy of this source.

Several other radio and optical properties of the observed candidates, and of the three sources that were found to be GRGs from available data in the NED (B1144+352, B1245+676 and B1310+451) are given in Tables .3 and .4.

   
4 First results

4.1 The number of GRGs

Of the 33 candidate sources which we have been able to identify spectroscopically, only three, and possibly five have projected linear sizes below 1 Mpc. These are B0217+367, B1709+465 and B1911+479. The uncertain cases are the source B0905+352, for which we do not have a well determined redshift yet and B1736+375 which may consist of two unrelated radio sources. Together with the 19 known GRGs in the area of the WENSS which share our selection criteria, we have so far identified 47 GRGs. This is by far the largest sample of sources with a projected linear size above 1 Mpc selected from a single survey. We also mention the existence of the large, but highly incomplete sample of GRGs which has been compiled by Ishwara-Chandra & Saikia (1999) from the literature. Although of similar size, the sample presented in this paper is better suited for statistical investigations of the radio and optical properties of GRGs since it has been selected from a single survey and in a more uniform matter.

4.2 Distribution functions of the sample

4.2.1 Flux density distribution

Figure 1a presents a histogram of the 325-MHz flux density distribution of the sample of 47 sources. The hatched bars indicate the flux density distribution of the sample of previously known GRGs. Not surprisingly, we find that all newly discovered GRGs have flux densities below 3 Jy, only; all ten GRGs with a 325-MHz flux density above this value had already been identified as such. For the area of the sky covered by WENSS, we can therefore agree with Riley (1989) who argued that no bright extended sources are missing from the LRL sample of bright radio sources ( S178>10.9 Jy, Dec $>+10\hbox{$^\circ$ }$, $\vert b\vert>10\hbox{$^\circ$ }$). Furthermore, we have extended the range of flux densities at which low redshift GRGs are found to sub-Jy levels. The median flux density of the combined sample is 1.15 Jy, which is almost a factor of four below the median value of the sample of previously known GRGs (see Table 2).

  \begin{figure} \par\resizebox{7.9cm}{!}{\epsfig{file=DS1923.1a,angle=90}}\hspace... ...cm} \resizebox{7.5cm}{!}{\epsfig{file=DS1923.1d,angle=90}}\\\par\end{figure} Figure 1: Histograms of several properties of the new and old sample of GRGs. In all plots, the hatched bars indicate the distribution of previously known GRGs (see Table 1). a) (upper left): The 325-MHz flux density distribution of the GRGs. We have used a binsize of 0.2 in the logarithm of the flux density in Jy. b) (upper right): The redshift distribution of the GRGs, using a binsize of 0.03 in redshift. The source 8C0821+695 at z=0.538 lies outside the range of this plot. c) (lower left): The projected linear size distribution of the GRGs, using a binsize of 0.2 Mpc. The source 3C236 (D=5.7 Mpc) lies outside the range of this plot. d) (lower right): The rest-frame 325-MHz radio power distribution of the GRGs, using bins of width 0.2 in the logarithm of the radio power in WHz-1.
Open with DEXTER

4.2.2 Redshift distribution

The new sample of GRGs mostly contains GRGs at $z \mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil $\displaystyle ... (see Fig. 1b). The only exceptions are the sources 8C0821+695 (z=0.538; Lacy et al. 1993), B0750+434 (z=0.347) and B0925+420 (z=0.365). The redshift distribution peaks at $z \sim 0.1$. The decrease in the number of sources towards higher redshift is likely to be due to the lower angular size limit used in the selection of the sample. Further, only more powerful GRGs will be selected towards higher redshift, of which the space density is likely to be lower. The median redshift of the sample of new GRGs is 0.1404, which is higher than that of the old GRGs alone (0.099; see Table 2). Since the average flux density is lower this is not surprising. The median redshift of the combined sample is 0.1175.

4.2.3 Linear size distribution
No source with a (projected) linear size exceeding that of the GRG 3C236 has been found. This source is therefore still the largest known radio galaxy in the Universe. In Fig. 1c we have plotted the (projected) linear size distribution of our sample. The median values of the linear sizes of the old and new GRGs lie close together (see Table 2). The majority of sources have linear sizes between 1 and 2 Mpc; the distribution of the combined sample falls off strongly at a linear size of 2 Mpc. This sharp decrease was not clear from the sample of "old'' GRGs only, due to the small number of sources. In Sect. 5.4 we will discuss whether the observed cut-off is a result of selection effects or an intrinsic property of the population of GRGs.

4.2.4 Radio power distribution

We calculated the emitted radio power at a rest-frame frequency of 325 MHz assuming isotropic emission. Since the redshifts are low, the radio K-correction is only small. For the new GRGs the measured spectral index between 325 and 1400 MHz has been used; for the "old'' GRGs a spectral index of -0.8 has been assumed if no reliable literature value could be found. The distribution of 325-MHz radio powers has been plotted in Fig. 1d. Despite the fact that a large number of GRGs has been found at flux density values well below that of the "old'' sample, the distribution of the radio powers of the new sources largely overlaps that of the old sources. This is related to the, on average, higher redshifts of the new sources. The combined sample is distributed rather uniformly between 1025and 1027 WHz-1; the sharp peak at the radio power bin centered on 1026.1 WHz-1 is most likely a result of small number statistics. At 325 MHz, the traditional separation between FRII and FRI-type sources (Fanaroff & Riley 1974) lies near 1026 WHz-1, which is close to the median value of the combined sample (see Table 2).

  
Table 2: Median values of some of the properties of the GRGs in the sample of "old'' GRGs, the sample of new GRGs and the combined sample of 47 sources. Column 1 gives the property; Cols. 2 to 4 give the median value of these properties for the old, new and combined sample, respectively.

\begin{displaymath}\begin{tabular}{l l l l} \hline\hline% \multicolumn{1}{c}{(1)... ... Redshift & 0.099 & 0.1404 & 0.1175 \\ \hline % \end{tabular}\end{displaymath}


   
5 Discussion

   
5.1 The "sensitivity limit'' of WENSS

For a radio source to be included in our sample, it must be larger than $5\hbox {$^\prime $ }$ and it must have been noticed on the radio maps as a large radio source. The latter is related to a surface brightness criterion: the average surface brightness, or integrated signal-to-noise ratio, must be high enough to be detected as a single radio source structure. The integrated signal-to-noise ratio, $(S/N)_{\rm int}$, for a resolved radio source is given by

 \begin{displaymath}% \left(\frac{S}{N}\right)_{\rm int} \approx \frac{S_{\rm int}}{\sigma \sqrt{A}}, \end{displaymath} (1)

where $S_{\rm int}$ is the integrated flux density of the source and the surface area A is in units of beams. The surface area can be rewritten as $A = c \cdot \theta_{\rm max}^2$, where $\theta_{\rm max}$ is the angular size (major axis) of the radio source and c is a number that relates the angular size to the surface area (cf. the length-to-width ratio). For instance, for an elliptically shaped radio source with a length-to-width ratio of 3, $c = \frac{\pi}{(12 \ln 2)} \cdot \theta_{\rm beam}^2$ with $\theta_{\rm beam}$ the (FWHM) beam-size of the observation. If we substitute the above expression for A in Eq. (1) we find

\begin{displaymath}% \left(\frac{S}{N}\right)_{\rm int} \propto \frac{S_{\rm int}}{\theta_{\rm max}}\cdot \end{displaymath} (2)

Figure 2 shows $S_{\rm int}/\theta_{\rm max}$against $\theta_{\rm max}$ for the sources in our sample which we have identified as GRGs. We find that the lowest values of $S_{\rm int}/\theta_{\rm max}$ for selected sources lie in the range between 0.02-0.03 Jy/arcmin; the source which lies well below this line is B1044+745, which is one of the two sources that were selected only for its radio structure in the NVSS and should therefore be situated below the WENSS "sensitivity'' limit. The other source which lies just below the line is B1245+676, which was selected from the WENSS but can be considered a "border-line'' case. The two sources just above the limit are B0935+743 and B1306+621.

The sensitivity limit appears to be almost independent of angular size at least up to a size of ${\sim}40$ arcmin. The sensitivity of WENSS to objects with an angular size above 1 degree on the sky decreases, so that the sensitivity limit inevitably must rise eventually.

From the figure we conclude that sources with $\theta_{\rm max} \ge 5\hbox{$^\prime$ }$ will most likely be selected if $S_{\rm int}/\theta_{\rm max} \mathrel{\mathchoice {\vcenter{\offinterlineskip\h... ...ffinterlineskip\halign{\hfil$\scriptscriptstyle ... Jy/arcmin. We will use this criterium to specify the regions in the radio power - linear size - redshift (P,D,z) parameter space which is accessible by our selection.

  \begin{figure} \par\resizebox{7.7cm}{!}{\epsfig{file=DS1923.2}} \end{figure} Figure 2: A plot of the 325-MHz flux density divided by the angular size against the angular size for the "old'' (diamonds) and the newly discovered GRGs (triangles). The diagonal lines indicate a constant integrated flux density and are drawn for 0.1 (solid), 1 (dashed) and 10 (dot-dashed) Jy. From this plot we determine the sensitivity limit of our selection method, ( $S_{\rm int}/\theta _{\rm max} = 0.025$ Jy/arcmin), indicated by the dotted horizontal line.
Open with DEXTER

5.2 The radio power - linear size diagram

In Fig. 3 we have plotted for all identified GRGs in our sample the linear size, D, against the radio power at 325 MHz, P, the so-called P-D diagram. For reference, all sources of the LRL sample with z < 0.6, which is the same redshift range as in which the GRGs are found, are plotted as well. Note that several of the formerly known GRGs are part of the LRL sample; these have been plotted as LRL sources.

From this plot the following can be concluded. First, although we have conducted the most extensive systematic search for GRGs to date, there are no sources in the upper right part of the P-D diagram, i.e. the region occupied by sources with large size and high radio power. If such sources had existed in our search area, They would most likely have discovered because of their inevitable high flux density. Second, the few GRGs which have a linear size above 2 Mpc have, on average, a higher radio power than smaller-sized GRGs.

To investigate which region of the P-D diagram is accessible through our WENSS selection, we have plotted in Fig. 4 lines which represent the lower sensitivity limit at constant redshift. Since the sensitivity limit is set by $S_{\rm int}/\theta _{\rm max} = 0.025$ Jy/arcmin (see Sect. 5.1), and a given redshift $S_{\rm int} \propto P$ and $\theta_{\rm max} \propto D$, the limit at that redshift follows the relation $P \propto D$. In Fig. 4 we have assumed a radio source spectral index of -0.8 to convert flux density into radio power.

At a particular redshift, WENSS can only detect giant sources which are more powerful than the radio power at which the line has been drawn (i.e. only in that part of the P-D diagram which is situated above the line). Note that lines of higher redshifts also start at a larger linear size because of the $5\hbox {$^\prime $ }$ lower angular size limit we have imposed. Based on the accessible regions in the P-D diagram there is no apparent reason why sources larger than 2 Mpc should be missed.

  \begin{figure} \par\resizebox{7.5cm}{!}{\epsfig{file=DS1923.3}} \end{figure} Figure 3: The 325-MHz radio power against linear size P- D diagram for the formerly known GRGs not part of the LRL sample (diamonds), the newly discovered GRGs (triangles) and sources from the LRL sample with z<0.6 (plusses).
Open with DEXTER


  \begin{figure} \par\resizebox{7.8cm}{!}{\epsfig{file=DS1923.4}} \end{figure} Figure 4: P- D diagram, filled with formerly known GRGs (diamonds) and newly discovered GRGs (triangles). The lines indicate the lower radio power limit for a source at a particular redshift as a function of linear size; the area directly above such a line is the accessible region in the (P,D) parameter space at that redshift. See text for further details.
Open with DEXTER


  \begin{figure} \par\resizebox{5.8cm}{!}{\epsfig{file=DS1923.5a}}\par\resizebox{6.4cm}{!}{\epsfig{file=DS1923.5b}} \end{figure} Figure 5: a) (Top) The 325-MHz radio power against the redshift of the formerly known (diamonds) and newly discovered (triangles) GRGs. The three diagonal lines represent the radio power for sources with a 325-MHz flux density of 0.1 Jy (long-dashed), 1.0 Jy (dashed) and 10.0 Jy (dot-dashed), assuming a spectral index of -0.8. The hatched area indicates the part of the diagram in which sources fall below our sensitivity limit. b) (Bottom) The projected linear sizes of the GRGs against their redshift. The meaning of the symbols is the same as in the upper plot. The hatched area indicates the region of the plot in which sources have not been selected, either because they are physically smaller than 1 Mpc, or spatially smaller than  $5\hbox {$^\prime $ }$. The dashed lines indicate the sensitivity limit for sources of the particular radio power is indicated (in logarithmic units of WHz-1 at 325 MHz) on top of each line. We assume a spectral index of -0.8. Sources can only be detected if they lie to the left of the line belonging to their particular radio power.
Open with DEXTER

5.3 Radio power and linear size versus redshift

In Fig. 5a we have plotted the 325-MHz radio powers of the GRGs against their redshifts. The higher sensitivity of the WENSS, as compared to earlier surveys, has enabled the discovery of GRGs with 5-10 times lower radio power. The hatched region in the figure indicates the part of the parameter space which is not accessible by WENSS, as a result of its limited sensitivity and lower angular size limit. Again, in determining this region we have assumed a spectral index of -0.8 for the radio sources, but the upper edge of the region is not very sensitive to the spectral index.

The broken shape of the upper edge of the hatched region can be understood as follows. At all redshifts, the WENSS is most sensitive to physically, and thus spatially, small sources. Since both a lower angular and physical size limit have been imposed, there are two regimes in which each of these two limits is in effect. At very low redshifts, a source with a physical size of 1 Mpc extends over $5\hbox {$^\prime $ }$ on the sky. This leads to a surface brightness limit and the integrated flux density of the source thus has to be large for the source to be still detectable. At higher redshift, the selection is constrained by the $5\hbox {$^\prime $ }$ lower angular size limit. This results in a lower limit to the flux density of a detectable source, determined by $S_{\rm int} \ge 0.025~[{\rm Jy/arcmin}] \cdot 5~[{\rm arcmin}] = 0.125$ Jy. Thus, we are flux density limited. The break occurs at that redshift at which a 1-Mpc large radio source will span an angle of $5\hbox {$^\prime $ }$ on the sky ( $z\sim 0.146$).

The one source that just lies in the hatched area where no sources should have been found is B1044+745, which, as mentioned before, would indeed not have been selected on basis of the WENSS data.

The strong effect that the lower angular size limit has on the selection can best be seen in Fig. 5b, where we have plotted the projected linear size of the identified GRGs against their redshift. Again, the hatched area indicates the region of the diagram which is inaccessible. The strong "bump'' at redshifts above ${\sim} 0.15$ result from the lower angular size limit.

Furthermore, in Fig. 5b we have plotted the sensitivity limit for sources of constant radio power (dashed lines). The (logarithm of the) radio power (in WHz-1 at 325 MHz) for each particular line has been indicated at the top of the diagram. A radio source of radio power P and linear size D can only be selected if it has redshift below that indicated by the dashed line for power P at size D. Had that source been at a higher redshift, or had it been of larger linear size, it would not have been selected. Likewise, all sources which lie on the left of such a line of constant P, should all have a radio power below this value. Apart from the before-mentioned case of B1044+745, this is indeed the case for the identified GRGs in our sample.

   
5.4 The 2-Mpc linear size cut-off

A strong drop in the number of sources with projected linear size above 2 Mpc has been found (see Fig. 1c). This may be a result of a strong negative radio power evolution of radio sources with increasing size, combined with our sensitivity limit. A negative radio power evolution is indeed expected for active radio radio sources (cf. Kaiser et al. 1997; Blundell et al. 1999). On the other hand, the observed effect can also be caused if a substantial fraction of the GRGs stop their radio activity (and "fade'') before they reach a size of 3 Mpc.

Above, we have argued that the selection effects alone provide no apparent reason why sources of linear size above 2 Mpc should have been missed if they existed in large numbers. On the contrary, Fig. 5b shows that sources above 2 Mpc in size can potentially be selected out to much higher redshift than smaller sized sources. Indeed, the figure shows that the majority of identified 2-3 Mpc large sources have redshifts at which 1-Mpc large sources would not have been selected.

Therefore, the observed 2-Mpc cut-off must be caused by a combination of the internal luminosity evolution of the sources and the sensitivity of the WENSS. An extreme case of such a luminosity evolution occurs when a large fraction of giant sources do not remain active for a long enough amount of time to reach a linear size of 2 Mpc. To disentangle the effects of the luminosity evolution of active and so-called "relic'' sources on the observed number of sources as a function of linear size requires much better statistics on the death-rate of radio galaxies as a function of radio power and linear size.

Acknowledgements

The INT and WHT are operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The Westerbork Synthesis Radio Telescope (WSRT) is operated by the Netherlands Foundation for Research in Astronomy (NFRA) with financial support of the Netherlands Organization for Scientific Research (NWO). The National Radio Astronomy Observatory (NRAO) is operated by Associated Universities, Inc., and is a facility of the National Science Foundation (NSF). This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. M. N. Bremer, H. Sangheera and D. Dallacasa are thanked for their help in the early stages of this project. P. Best and M. Lehnert are thanked for many helpful discussions and suggestions. L. Lara is acknowledged for providing high resolution radio maps of several sources prior to publication.

References

 

Online Material

Appendix A: The sample of newly discovered GRGs and their properties

Here, we present notes on the radio structure, the host galaxies and the optical spectra of the sources. Table .3 presents the flux densities and positions of the radio cores and the host galaxies. Table .4 lists several other radio properties and the redshifts of the sources. Further, we present a table with the log of the INT observations (Table .2) and a table with the wavelengths and redshifts of spectral emission and absorption features we have measured in the spectra of the sources (Table .5). Finally, we present the radio and optical images of the sources, and the optical spectra of their host galaxies. Radio contour plots mostly are from the WENSS and/or the NVSS surveys. The FWHM beam size is indicated in a separate panel, usually situated in the lower left corner of the contour plot. The flux density level of the first contour can be found in Table .6. Unless indicated otherwise in this table, contour levels have been plotted at (-1,1,2,4,8,16,32,64,128,256) times the flux density level of the first contour. For the 1.4-GHz WSRT observations, Table .6 also gives the major and minor axes (FWHM) of the restoring beam. Also, we present overlays of our highest resolution radio map with the optical fields, usually retrieved from the digitized POSS-I survey, or POSS-II whenever available (see Table .6). The range of grey scales is such that the contents of the optical field is shown best. In case the identification of the host galaxy of the radio source is not apparent from the optical image, we have encircled it or used an arrow to point it out. The optical spectra of the host galaxies have the identified emission and absorption features indicated. In the plots of the spectra, the "$\oplus$''-symbol indicates the presence of an atmospheric feature, such as an imperfectly subtracted bright sky-line or an atmospheric absorption band. The " $\downarrow$''-symbol indicates the presence of a feature resulting from a cosmic ray impact that could not be properly removed from the data.

B0211+326: This ${\sim}5\hbox{$^\prime$ }$-large radio source has been shortly observed with the WSRT, but no radio core has been detected. On the POSS-II image we find a small group of faint galaxies situated halfway between the two radio lobes. The brightest of these is most likely the host galaxy, since its optical spectrum shows bright emission lines. We find a redshift of 0.2605, so that the projected linear size of the radio source is 1.6 Mpc.

B0217+367: An overlay of a 1.4-GHz WSRT radio map with the optical field shows that a ${\sim}10$ mag galaxy coincides with a central compact radio structure. A higher resolution 2.7-GHz map presented by Faulkner (1985) shows a radio core with two jets. The western jet is bend and has a bright knot at a distance of $20\hbox{$^{\prime\prime}$ }$from the core. Only the western radio lobe is connected to this radio core by a faint bridge. The lobe itself shows several twists and a diffuse outer structure which is only barely detected in the NVSS. The optical spectrum of the host galaxy shows weak [N II]6584 and [S II]6717/6731 emission lines. The redshift of the host galaxy is 0.0368, yielding a projected linear size of 0.95 Mpc.

B0648+733: The compact radio source located between the two radio lobes coincides with a galaxy on the POSS-I plates. A more sensitive VLA observation shows that the western lobe has an edge-brightened radio structure (Lara et al. 2001); our WSRT map only shows the bright hotspot. The optical spectrum of the identification shows strong emission lines. The redshift is 0.1145, yielding a projected linear size of 2.0 Mpc. The compact source overlapping with the eastern radio lobe on the NVSS radio map is most likely an unrelated background source.

B0648+431: This ${\sim}10\hbox{$^\prime$ }$-large radio source consists of four main components. An overlay of the 1.4-GHz WSRT radio map with an optical image shows that the eastern of the two middle component coincides with a 12 mag optical galaxy. An optical spectrum of the galaxy shows weak [N II]6548,6583 line-emission on top of a stellar continuum, at a redshift of 0.0891. The projected linear size of the radio source is 1.3 Mpc.

B0658+490: In the WENSS radio map this source is an ${\sim}19\hbox{$^\prime$ }$-large complicated radio structure with a fairly diffuse eastern part, three compact sources in the middle and a diffuse western extension. The FIRST survey has resolved the central source, and shows that it has a jet-like extension in the direction of a larger jet-like feature on the NVSS radio map. The central source coincides with an 11 mag. Optical galaxy, whose optical spectrum shows weak [NII]6548/6583 emission. The redshift is 0.0650. The two bright compact sources west of the radio core are resolved in the FIRST survey. The westernmost one appears to be an edge-brightened radio lobe, the other is more compact and has a radio tail pointing away from the radio core. It is unclear if this component is truly associated with the large radio source. If it were an unrelated source, the lack of an optical identification on the POSS-II survey suggests that it is at a much higher redshift than the host galaxy of the central radio source. Assuming that all radio structures are part of a single radio source, it has a linear size of 1.9 Mpc.

B0747+426: This is a $6\hbox{$^\prime$ }$-large radio source with a bent radio structure. The southern lobe is larger and more diffuse. Neither of the two lobes contains a bright hotspot. Near the central bent a 17 mag galaxy is detected which coincides with a weak, unresolved source in the FIRST survey, presumably the radio core. Its optical spectrum reveals [O II]3727 emission and a stellar continuum. The redshift is 0.2030, yielding a projected linear size of 1.5 Mpc.

B0750+434: Although only a weak radio source in the WENSS, this object is one of the largest radio sources we have discovered in this project. The central source, unresolved by FIRST, coincides with a 16.7 mag star-like object. An optical spectrum reveals strong emission lines, among which broad Hydrogen Balmer lines, and a blue-colored continuum. The redshift is 0.3474, which is the highest of all sources presented here. The southern radio lobe is resolved by FIRST into three separate components, of which probably only the most southern one is related to the large scale radio structure. The projected linear size of this source is 2.9 Mpc.

B0757+477: The NVSS reveals a strong radio core in this source. The FIRST survey radio map shows that the northern lobe has a compact hotspot and that the southern lobe is diffuse. The core is unresolved by FIRST and coincides with a 15.5 mag star-like object. The optical spectrum is dominated by strong and broad Hydrogen Balmer lines and a blue non-thermal continuum. The redshift is 0.1567, resulting in a projected linear size of the radio source of 1.3 Mpc.

B0801+741: The 1.4-GHz WSRT observations of this source reveal a compact core, coinciding with a 15.8 mag optical galaxy. The radio lobes are largely resolved out, however. The NVSS map suggests that these lobes are narrow and straight. The redshift of the host galaxy is 0.1204, and its sepctrum reveals H$\alpha$, [N II]6548/6583 and [S II]6717/6738 emission lines. The H$\beta$ emission line is weak, relative to H$\alpha$, suggesting a large amount of extinction towards the line-emitting gas. The projected linear size of the radio source is 1.1 Mpc.

B0809+454: In the WENSS and NVSS this source is a rather weak ${\sim}7\hbox{$^\prime$ }$-large radio source. The FIRST survey radio map shows the radio core and the two outer extremities of the radio lobes which contain hotspots. The radio core coincides with a 18.5 mag optical source, whose spectrum shows strong [O III]4959,5007 and [O II]3727 emission lines. The redshift is 0.2204, yielding a projected linear size of 1.9 Mpc.

B0813+758: This source has originally been selected from the NVSS, in which it is an 8.5'-large radio source with a bright unresolved central source and an asymmetrical radio structure. A short 1.4-GHz WSRT observation shows that the the eastern radio lobe has a rather strange structure. Higher quality VLA data confirm that all structures on the WSRT map are part of a single large radio lobe (Lara et al. 2001). The central radio source coincides with a 17.5 mag galaxy whose optical spectrum shows strong emission lines. The H$\alpha$-line has a broad component. We measure a redshift of 0.2324, resulting in a linear size of the radio source of 2.3 Mpc.

B0905+352: This $6.3\hbox{$^\prime$ }$-large radio source shows no significant structure in WENSS or NVSS. FIRST, however, reveals that the two radio lobes have strong hotspots, and that the western lobe has an extension towards the north-west. No radio core is detected. Two bright compact objects halfway the two radio lobes were identified as stars, and only the galaxy surrounded by the dashed circle in Fig. .12 was found to show a galaxy-like spectrum, although we have not yet firmly established its redshift. The two lines indicated as [N II] in the spectrum coincide with atmospheric OH-bands. If they are real, the redshift is 0.106, which is rather low considering that the galaxy has a POSS-E magnitude of 18.0. A redshift of 0.260 can also be argued, because of a possible 4000 Å-break observed at a wavelength of 5050 Å. This higher redshift would agree more closely with the optical magnitude of the galaxy.

B0925+420: This source is one of the so-called "Double-double'' radio galaxies (see Schoenmakers et al. 2000a), consisting of two separate double-lobed radio structures. Radio maps, optical images and further information are presented in Schoenmakers et al. (2000a).

B0935+743: This source has a radio morphology much resembling that of the known giant radio galaxy 4CT74.17 (e.g. van Breugel & Willis 1981). The central source coincides with an optical galaxy of 14.3 mag. The optical spectrum shows no signs of emission lines. A somewhat higher resolution observation shows that the central source has two jet-like features pointing towards the outer two sources (Lara et al. 2001), which suggests that all three are part of a single radio structure. The redshift of the optical galaxy associated with the radio core is 0.1215, yielding a projected linear size of 1.3 Mpc.

B1029+281: Because of the low declination of this source, the WENSS radio map does not show much structure. The NVSS map shows a large double-lobed radio source with a relatively strong radio core. The central source is resolved by FIRST into a compact source coinciding with a 14.3 mag optical galaxy, and a radio lobe-like feature at a distance of ${\sim}1\hbox{$^\prime$ }$ to the north. This much resembles the structure observed in the so-called "double-double'' radio galaxies (Schoenmakers et al. 2000a). The optical spectrum of the host galaxy shows strong and broad H$\alpha$ emission. The H$\beta$ emission line also has a broad component. Also, it is much weaker than H$\alpha$ which may indicate a high amount of internal extinction. The redshift is 0.0854, yielding a projected linear size of 1.4 Mpc.

B1044+745: Although this radio source is clearly detected in the NVSS, it is not in the WENSS. The NVSS radio map shows two diffuse lobe-like structures with a weak, compact source in between. The compact source coincides with a 14 mag galaxy. The optical spectrum of this galaxy is dominated by stellar continuum, with only a weak [N II]6584 emission-line. The redshift is 0.1210, and the projected linear size of the radio source is thus 1.9 Mpc.

B1110+405: A FIRST radio map of this $12\hbox{$^\prime$ }$-large radio source shows a relatively bright component in the western radio lobe which resembles a small edge-brightened radio lobe. However, there also is diffuse radio emission at much a larger distance from the radio core. The radio core is identified with a 11.4 mag galaxy, which appears to be double. However, the western optical object is spectroscopically identified as a star. The optical spectrum of the galaxy shows stellar continuum and weak [N II]6584 and [S II]6717/6731 emission lines although the latter lie in an atmospheric absorption band. The projected linear size of the radio source is 1.4 Mpc.

B1144+352: This source is extensively discussed elsewhere (Schoenmakers et al. 1999b).

B1213+422: The radio map from the FIRST survey shows two extended radio lobes and an unresolved central radio source, which coincides with a 15.9 mag galaxy. Its optical spectrum shows strong [O III]4959,5007 emission lines and stellar continuum. The H$\alpha$-line is clearly broadened. The redshift is 0.2426 and the projected linear size is 1.5 Mpc.

B1245+676: This ${\sim}12\hbox{$^\prime$ }$-large radio source has an inverted spectrum radio core, which is identified with a 14 mag galaxy. An optical spectrum of this source can be found in Marcha et al. (1996); it shows no sign of emission lines. The redshift is 0.1073, and the projected linear size of the radio source is therefore 1.8 Mpc. A more detailed analysis of the radio structure of this source will be presented in de Bruyn et al. (in preparation).

B1306+621: This ${\sim}9\hbox{$^\prime$ }$-large radio source is rather faint. The WENSS and NVSS radio maps show two radio lobes and a radio core. A 1.4-GHz WSRT observation shows that both lobes are edge-brightened. The radio core coincides with a 16 mag galaxy, which does not show any emission-lines, though. The redshift is 0.1625, yielding a projected linear size of 1.9 Mpc.

B1310+451: On an angular scale, this is the largest radio source we have found. It has a size of ${\sim}23\hbox{$^\prime$ }$ and contains a bright central core and two diffuse outer lobes. The bright compact source just beyond the western lobe is most likely an unrelated radio source. In the FIRST survey, the radio core is resolved and two jets are visible. The radio core coincides with a 10 mag galaxy. The optical spectrum shows that it has weak [N II]6584 and [S II]6717/6731 emission lines. It has a redshift of 0.0358, yielding a projected linear size of 1.4 Mpc. The existence of the large scale radio emission and the redshift of this radio source have been reported earlier by Faulkner (1985).

B1416+380: This ${\sim}7\hbox{$^\prime$ }$-large radio source resembles a fat double radio source. The northern radio lobe is barely detected in the NVSS. The integrated spectral index of the whole source between 325 and 1400 MHz is -1.46, which makes this radio source the steepest spectrum radio source in our sample. The central component is unresolved in the FIRST and it coincides with a 14.5 mag galaxy. The optical spectrum of this galaxy shows [O I]6300, H$\alpha$ and [N II]6548/6584 emission. Its redshift is 0.1350, resulting in a projected linear size of 1.4 Mpc.

B1426+295: The eastern lobe of this ${\sim}15'$-large source is situated near a bright, but unrelated radio source. The FIRST radio map shows an unresolved central object, which coincides with a 13 mag optical galaxy. The optical spectrum of this galaxy shows weak emission lines of [N II]6548/6583, H$\alpha$, which is partly in absorption, and [S II]6717/6731. The redshift is 0.087, resulting in a projected linear size of the radio source of 1.9 Mpc. We remark that spectroscopical observations of the galaxy situated ${\sim}30\hbox{$^{\prime\prime}$ }$ to the north-west of the host galaxy show that it has the same redshift and is therefore most likely part of the same group of galaxies as the host galaxy.

B1450+333: This source is also a "Double-double'' radio galaxy. Radio maps, optical images and further information are presented in Schoenmakers et al. (2000a).

B1543+845: This source has been found in the NVSS maps, before the WENSS maps of this region of the sky became available. It shows an 8'-large double-lobed radio source with a weak central compact source which coincides with an optical galaxy. The identification of the compact radio source as the radio core is confirmed by a higher resolution VLA radio map (Lara et al. 2001). In the optical spectrum, which has been obtained by I.M. Gioia with the 2.2 m telescope of the University of Hawaii on Mauna Kea, we have identified the [O III] 4959/5007 emission lines. We measure a redshift of 0.201, which yields a projected linear size of 2.1 Mpc for the radio source.

B1709+464: This $10\hbox{$^\prime$ }$-large radio source has a diffuse western lobe and a more edge-brightened eastern lobe. The radio core is clearly detected and a map from the FIRST survey shows that this source has a small two-sided structure somewhat resembling the larger scale radio structure. The core coincides with a 10 mag optical galaxy. The spectrum reveals weak [N II]6584 and [S II]6717/6731 emission lines. The redshift of the host galaxy is 0.0368, yielding a projected linear size of 0.59 Mpc. This is therefore not a GRG.

B1736+375: This is a $7\hbox{$^\prime$ }$-large elongated radio structure which in the NVSS map has a dominant central source. It coincides with a 15.9 mag galaxy, whose optical spectrum reveals H$\alpha$ and [N II] emission-lines, although these are situated near a strong atmospheric absorption band. The redshift is 0.1562. The northern radio structure appears to be a small double-lobed source in the NVSS, and at its center a faint optical galaxy is situated. We have no spectrum of this source. The northern structure may be an unrelated radio source. If the whole structure were to be a single radio source, the projected linear size would be 1.4 Mpc.

B1852+507: The NVSS map of this $7\hbox{$^\prime$ }$-large radio source shows two lobes and a central component which coincides with a 12.8 mag galaxy. We have identified the bright nearby optical source as a star. The optical spectrum of the galaxy shows no emission lines. Its redshift is 0.0958, yielding a linear size of the radio source of 1.0 Mpc.

B1911+470: This ${\sim}6\hbox{$^\prime$ }$-large radio source has a dominant central component and a somewhat bent southern radio lobe. The central component coincides with a 12 mag optical galaxy, which has a companion at a distance of ${\sim}30\hbox{$^{\prime\prime}$ }$ to the north-west. The optical spectrum shows a weak [N II]6584 emission-line, but it overlaps with an atmospheric absorption band. Its redshift is 0.0548. The companion has the same redshift and they are therefore most likely also physically close to each other. The projected linear size of the radio source is 0.54 Mpc, and therefore this is not a GRG.

B1918+512: This $7.3\hbox{$^\prime$ }$-large radio source has a FRII-type radio morphology. The eastern "extension'' is an unrelated radio source. A deep 21-cm WSRT observation shows a possibly two-sided jet in this source and a central radio source, probably the radio core. A CCD-image obtained by P. Best with the LDSS imaging spectrograph on the 4.2 m WHT telescope on La Palma shows a faint galaxy close to the core; on the DSS this source is merged with a nearby star. An optical spectrum shows possible emission lines of [O II]3727 and [O III]5007, as well as several absorption features, all in agreement with a redshift of 0.284. We note that the star-like object situated in the "gap'' between the two radio lobes is spectroscopically identified as a star. If the redshift of the host galaxy is correct, the linear size of this radio galaxy is 2.3 Mpc.

B2147+816: This $18\hbox{$^\prime$ }$-large FRII-type radio galaxy has been briefly described before by Saunders (1982), and more recently (and more extensively) by Palma et al. (2000). Both the NVSS and WENSS radio map show the two radio lobes and the central core. The radio core coincides with a 16.5 mag galaxy, which is a member of a small group of three galaxies. The optical spectrum of the identification shows strong emission lines. Its redshift is 0.1457, confirming the values given by Saunders (1982) and Palma et al. (2000). The projected linear size of the radio source is 3.7 Mpc.


 

 
Table A.1: Table with WENSS selected candidate GRGs after removing sources identified as non-GRGs on basis of optical data. Column 1 gives IAU-notation (in B1950.0) of the source name. Columns 2 and 3 give approximate source coordinates in Right Ascension and Declination in B1950.0 coordinates. Column 4 gives the integrated WENSS flux of the source. Column 5 gives the size of the source in arcminutes. Column 6 indicates whether the source is considered a GRG-candidate, for reasons given in Col. 7.
(1) (2) (3) (4) (5) (6) (7)
Source RA Dec S325 Size Still Reason/comments
  [h  m  s] $[\,\hbox{$^\circ$ }~~ \hbox{$^\prime$ }~~ \hbox{$^{\prime\prime}$ }\,]$ [Jy] $[\, \hbox{$^\prime$ }\,]$ selected?  
B0001+342 00 01 10 34 13 00 0.69 12 no NVSS morphology
B0023+750 00 23 15 75 00 30 0.30 5 yes NVSS selected, supported by WENSS
B0036+285 00 36 05 28 29 00 1.54 7 no NVSS and 1.4-GHz WSRT morphology
B0050+433 00 50 10 43 25 00 0.59 12 no NVSS morphology
B0058+403 00 58 05 40 19 00 1.04 5 no NVSS morphology
B0119+377 01 19 10 37 44 00 2.29 6 no NVSS morphology
B0126+426 01 26 45 42 36 00 0.79 13 no NVSS morphology
B0141+762 01 41 25 76 13 00 0.18 6 yes NVSS selected, supported by WENSS
B0200+457 02 00 10 45 45 30 0.19 6 yes NVSS morphology
B0200+678 02 00 30 67 53 00 2.15 6 no 1.4-GHz WSRT morphology
B0201+317 02 01 35 31 42 00 0.15 6 no NVSS morphology
B0211+326 02 11 20 32 37 00 1.59 5 yes 1.4-GHz WSRT morphology
B0217+367 02 17 20 36 46 00 2.44 16 yes NVSS morphology
B0330+871 03 30 35 87 07 00 0.11 6 yes NVSS selected, supported by WENSS
B0334+329 03 34 30 32 59 00 0.54 6 yes NVSS morphology
B0429+293 04 29 40 29 22 00 1.31 7 no NVSS morphology
B0503+704 05 03 30 70 27 00 1.01 6 no NVSS morphology
B0603+612 06 03 00 61 15 00 1.64 5 yes NVSS morphology
B0627+721 06 27 40 72 11 30 0.77 5 yes NVSS and 1.4-GHz WSRT morphology
B0634+515 06 34 35 51 30 00 0.36 10 yes NVSS morphology
B0646+370 06 46 55 37 03 00 0.47 6 no NVSS morphology
B0648+734 06 48 15 73 23 30 2.4 13 yes NVSS morphology
B0648+431 06 48 40 43 08 30 0.71 10 yes NVSS morphology
B0658+490 06 58 20 49 03 30 1.01 19 yes NVSS morphology
B0713+432 07 13 45 43 14 00 0.59 7 yes NVSS and FIRST morphology
B0730+375 07 30 00 37 30 00 0.52 10 no NVSS and FIRST morphology
B0747+426 07 47 40 42 39 00 0.64 6 yes NVSS/FIRST morphology
B0750+434 07 50 40 43 24 00 0.24 8 yes NVSS/FIRST morphology
B0757+477 07 57 55 47 44 30 0.25 6 yes NVSS/FIRST morphology
B0801+741 08 01 15 74 09 00 0.55 6 yes NVSS selected, supported by WENSS
B0809+454 08 09 40 45 25 00 0.26 7 yes NVSS and FIRST morphology
B0813+758 08 13 40 75 48 00 2.14 8 yes NVSS selected, supported by WENSS
B0817+427 08 17 45 42 43 00 1.18 9 no NVSS and FIRST morphology
B0817+337 08 17 50 33 43 00 0.26 6 no NVSS and FIRST morphology
B0840+513 08 40 45 51 18 00 0.98 10 no NVSS and FIRST morphology
B0853+292 08 53 00 29 16 00 3.90 15 no NVSS and FIRST morphology
B0854+402 08 54 00 40 12 00 0.35 6 no NVSS and FIRST morphology
B0903+783 09 03 11 78 21 30 0.20 8 no Western `lobe' overlaps bright spiral galaxy
B0905+352 09 05 45 35 17 30 0.57 6 yes NVSS and FIRST morphology
B0909+353 09 09 45 35 22 00 0.50 6 yes NVSS and FIRST morphology
B0917+307 09 17 15 30 42 30 0.46 10 no NVSS and FIRST morphology
B0925+420 09 25 55 42 00 00 0.55 7 yes NVSS and FIRST morphology
B0935+743 09 35 00 74 19 00 0.19 7 yes NVSS selected, supported by WENSS
B0936+512 09 36 40 51 17 30 0.94 6 no WSRT 1.4-GHz and FIRST morphology
B1001+548 10 01 30 54 48 30 0.52 13 yes NVSS morphology
B1029+281 10 29 25 28 11 30 0.67 11 yes NVSS and FIRST morphology
B1029+322 10 29 40 32 12 00 0.64 11 no WSRT 1.4-GHz and FIRST morphology
B1030+312 10 30 25 31 12 00 0.87 6 no NVSS and FIRST morphology
B1036+632 10 36 30 63 15 30 0.14 5 yes NVSS morphology
B1044+745 10 44 15 74 35 30 0.12 11 yes NVSS selected, supported by WENSS
B1054+488 10 54 10 48 52 30 0.71 8 yes NVSS and FIRST morphology



 
Table A.1: continued.
(1) (2) (3) (4) (5) (6) (7)
Source RA Dec S325 Size Still Reason/comments
  [h  m  s] $[\,\hbox{$^\circ$ }~~ \hbox{$^\prime$ }~~ \hbox{$^{\prime\prime}$ }\,]$ [Jy] $[\, \hbox{$^\prime$ }\,]$ selected?  
B1110+405 11 10 20 40 34 00 0.82 12 yes NVSS and FIRST morphology
B1112+333 11 12 15 33 19 00 3.06 6 no WSRT 1.4-GHz and FIRST morphology
B1144+353 11 44 45 35 18 30 0.97 12 yes z=0.063 (NED), so $D \sim 1.2$ Mpc
B1150+312 11 50 50 31 12 00 0.28 9 no NVSS and FIRST morphology
B1209+614 12 09 30 61 04 00 2.54 6 no 4C61.25, NVSS morphology
B1213+422 12 13 40 42 16 00 1.10 5 yes NVSS and FIRST morphology
B1218+639 12 18 30 63 56 30 1.19 8 no NVSS morphology
B1232+535 12 32 40 53 35 00 0.36 10 yes NVSS morphology
B1234+836 12 34 00 83 39 30 0.07 6 yes NVSS selected, supported by WENSS
B1245+676 12 45 30 67 39 00 0.20 12 yes NVSS selected, z = 0.1073 (NED), so $D\sim1.8$ Mpc
B1250+452 12 50 45 45 17 00 1.33 10 no NVSS morphology and bright optical ID
B1306+621 13 06 50 62 10 00 0.19 9 yes NVSS morphology
B1310+451 13 10 05 45 09 30 0.65 23 yes z=0.0356 (NED), so $D \sim 1.4$ Mpc
B1330+361 13 30 20 36 09 00 0.27 7 no NVSS and FIRST morphology
B1340+382 13 40 50 38 15 00 0.34 10 yes NVSS and FIRST morphology
B1340+447 13 40 55 44 44 00 0.30 6 no NVSS and FIRST morphology
B1342+407 13 42 30 40 44 00 0.51 8 no NVSS and FIRST morphology
B1343+371 13 43 45 37 07 00 1.90 7 no WSRT 1.4-GHz and FIRST morphology
B1404+362 14 04 55 36 15 00 0.24 6 no NVSS and FIRST morphology
B1415+685 14 15 30 68 33 00 0.26 6 yes NVSS morphology
B1416+380 14 16 35 38 00 00 0.46 7 yes NVSS and FIRST morphology
B1426+295 14 26 10 29 32 00 1.10 15 yes NVSS and FIRST morphology
B1443+310 14 43 20 31 04 00 0.41 7 yes NVSS and FIRST morphology
B1450+333 14 50 55 33 21 00 1.38 6 yes NVSS and FIRST morphology
B1532+315 15 32 40 31 35 00 0.73 13 no NVSS and FIRST morphology
B1535+613 15 35 40 61 22 00 0.09 6 no NVSS morphology
B1543+845 15 43 55 84 33 00 1.14 8 yes NVSS selected, supported by WENSS
B1614+485 16 14 25 48 33 00 0.17 10 yes NVSS and FIRST morphology
B1623+410 16 23 30 41 03 00 1.25 7 no NVSS and FIRST morphology
B1634+503 16 34 15 50 23 00 0.59 7 no NVSS and FIRST morphology
B1637+539 16 37 50 53 55 00 1.99 9 no NVSS and FIRST morphology
B1639+328 16 39 05 32 50 00 0.90 6 no NVSS and FIRST morphology
B1709+464 17 09 30 46 28 00 1.11 10 yes NVSS and FIRST morphology
B1736+375 17 36 40 37 35 00 0.48 7 yes NVSS morphology
B1838+658 18 38 05 65 52 00 0.95 7 yes NVSS; z=0.23 (NED), so $D \sim 1.9$ Mpc.
B1844+653 18 44 00 65 19 10 0.26 7 yes NVSS morphology
B1852+507 18 52 20 50 42 00 0.27 7 yes NVSS morphology
B1855+310 18 55 20 31 00 00 1.35 9 yes NVSS morphology
B1911+470 19 11 50 47 01 00 0.80 6 yes NVSS morphology
B1911+481 19 11 50 48 09 00 0.77 16 yes NVSS morphology
B1918+453 19 18 40 45 22 00 0.78 18 yes NVSS morphology
B1918+516 19 18 05 51 36 00 1.22 7 yes NVSS morphology
B1919+479 19 19 55 47 59 30 3.52 10 yes 4C47.51, z=0.102 (NED), so $D\sim1.5$ Mpc
B1919+741 19 19 15 74 09 30 2.04 6 yes NVSS morphology
B1924+549 19 24 30 54 59 00 0.48 7 no NVSS morphology
B2130+341 21 30 05 34 07 00 0.37 6 yes NVSS morphology
B2147+816 21 47 20 81 41 00 1.06 18 yes NVSS selected, supported by WENSS
B2205+376 22 05 25 37 36 00 0.32 7 yes NVSS morphology
B2231+320 22 31 10 32 00 00 0.29 11 no NVSS morphology
B2233+373 22 33 20 37 20 00 0.62 6 yes NVSS morphology
B2312+419 23 12 40 41 57 10 0.27 6 no NVSS morphology
B2315+401 23 15 55 40 10 17 0.11 6 yes NVSS morphology
B2326+315 23 26 00 31 35 00 0.47 10 no NVSS morphology
B2357+401 23 57 10 40 08 00 0.22 5 yes NVSS morphology


 

 
Table A.2: Log of the spectroscopic observations of GRG candidates in our sample. Column 1 gives the name of the source in IAU format. Column 2 gives the telescope used for the observations. Column 3 gives the observing date. Column 4 gives the central wavelength of the observation in Ångstrom (for the INT only). Column 5 gives the used width of the slit in arcsec. Column 6 gives the integration time. Column 6 gives an indication of the observing conditions; "P'' stands for photometric conditions, "NP'' for non-photometric conditions, or cirrus clouds, and "C'' stands for cloudy conditions.
(1) (2) (3) (4) (5) (6) (7)
Source Tel. Date $\lambda_{\rm central}$ Slit Int. Cond.
      $[\,$Å$\,]$ $[\,\hbox{$^{\prime\prime}$ }\,]$ $[\,$s$\,]$  
B0211+326 INT 4 Aug. 1995 6000 2 2400 NP
    8 Oct. 1996 6500 2 1200 P
B0217+367 INT 4 Aug. 1995 5500 2 900 C
B0648+733 INT 6 Apr. 1996 6000 2 1800 P
B0648+431 INT 7 Apr. 1996 6000 2 1200 NP
B0658+490 INT 6 Apr. 1996 6000 2 1800 P
B0747+426 INT 8 Oct. 1996 6000 2 1200 P
B0750+434 INT 9 Oct. 1996 6000 2 600 P
      6500 2 600 P
B0757+477 INT 7 Apr. 1996 5500 2 600 NP
      6500 2 600 NP
B0801+741 INT 7 Apr. 1996 6000 2 600 NP
B0809+454 INT 8 Apr. 1996 6000 3 600 NP
      6500 3 600 NP
B0813+758 INT 6 Apr. 1996 6000 2 600 P
      6500 2 1200 P
B0905+352 INT 7 Apr. 1996 6000 2 600 NP
B0925+420 INT 8 Apr. 1996 6000 2 600 NP
B0935+743 INT 7 Apr. 1996 6000 2 1200 NP
B1029+281 INT 7 Apr. 1996 6000 2 1200 NP
B1044+745 INT 7 Apr. 1996 6000 2 600 NP
B1110+405 INT 6 Apr. 1996 6000 2 1200 P
B1213+422 INT 7 Apr. 1996 6000 2 600 NP
      6500 2 600 NP
B1306+621 INT 8 Apr. 1996 6000 2 1200 NP
B1310+451 INT 5 Aug. 1995 5500 2 900 P
B1416+380 INT 5 Aug. 1995 6000 2 900 P
    9 Apr. 1996 6500 2 600 P
B1426+295 INT 4 Aug. 1995 5500 2 1800 P
    9 Apr. 1996 6000 2 1200 P
B1450+333 WHT 8 July 1997   2 600 P
B1543+845 2.2m UH 4 Mar. 1998   2 2100 P
    5 Mar. 1998   2 2400 P
B1709+464 INT 4 Aug. 1995 5500 2 900 P
B1736+375 INT 9 Oct. 1996 6000 2 1200 P
B1852+507 INT 9 Oct. 1996 6000 2 600 P
B1911+470 INT 8 Oct. 1996 6000 2 1200 P
B1918+516 INT 8 Oct. 1996 6000 2 600 P
B2147+816 INT 9 Oct. 1996 5500 2 600 P
      6000 2 1200 P



  
Table A.3: Properties of the radio cores and the optical identifications of the spectroscopically observed sources, and of the confirmed giant sources B1144+352, B1245+676 and B1310+451. Column 1 gives the name of the radio source in IAU notation; Col. 2 gives the observation used to determine the radio core position and its flux density; Cols. 3 and 4 give the radio core position in right ascension and declination, respectively, in B1950.0 coordinates. These have been obtained by fitting a Gaussian in the radio map. Column 5 gives the integrated flux density at 1.4 GHz of the radio core. Columns 6 and 7 give the position of the optical identification in right ascension and declination, respectively, in B1950.0 coordinates, obtained from fitting a Gaussian in the available optical image. Column 8 gives the magnitude of the identification in the red (POSS-E) band of the Palomar survey. The magnitudes for sources weaker than 15.0 have been obtained from the APM catalogue and are estimated to be accurate to 0.5 mag. For brighter sources, we have measured the magnitudes directly from the digitized POSS-I frames using the photometric calibration for stars available from the STScI WWW-pages and through the GETIMAGE-2.0 plate retrieval software. Typical uncertainties in these values are estimated to be large, at least 1 mag.


\begin{displaymath}\begin{tabular}{l l l@{$\,\pm\,$}r l@{$\,\pm\,$}r r@{$\,\pm\,... ...1 & 81 40 57.3 & 0.1 & 16.5 \\ \hline \hline \\ \end{tabular}\end{displaymath}

Notes:
a-Variable (see Schoenmakers et al. 1999b).
b-Merged with nearby star on DSS; the magnitude has been determined by subtracting the flux from the star, obtained by fitting a Gaussian, from the integrated flux of the star and galaxy combined. The error is therefore large (estimated at 1 mag).


  
Table A.4: Radio properties of the sources from Table .3. Column 1 gives the source name in IAU format. Column 2 gives the integrated flux density of the source at 325 MHz from the WENSS (unless states otherwise). Column 3 gives the integrated flux density at 1400 MHz from the NVSS. Column 5 gives the spectral index between 325 and 1400 MHz. Column 6 gives the redshift of the host galaxy. Column 7 gives the angular size of the radio source in arcminute. Column 8 gives the projected linear size in Mpc. Column 9 gives the radio luminosity at an emitted frequency of 325 MHz.


\begin{displaymath}\begin{tabular}{l r@{$\,\pm\,$}l r@{$\,\pm\,$}l l@{$\,\pm\,$}... ...& 3.66 & 0.04 & 26.00 & 0.02 \\ \hline \hline\\ \end{tabular}\end{displaymath}

Notes:
a-Subtracted $41 \pm 7$ mJy background object at RA 06 49 02.7, Dec 73 25 55.
b-Subtracted $19.8 \pm 1.1$ mJy background object at RA 06 49 02.7, Dec 73 25 55.
c-Subtracted $149 \pm 11$ mJy background object at RA 07 47 48.2, Dec 42 39 56.
d-Subtracted $26 \pm 1$ mJy background object at RA 07 47 48.2, Dec 42 39 56.
e-See Schoenmakers et al. (2000a) for radio maps and optical spectrum of this source.
f-Includes background source at RA 10 29 36.3 Dec 28 13 15.9 (flux density $10 \pm 1$ mJy at 1400 MHz).
g-WENSS polar cap region (observed frequency 351 MHz).
h-Subtracted $72 \pm 7$ mJy background object at RA 11 10 24.8, Dec 40 38 03.
i-See Schoenmakers et al. (1999b) for radio maps and optical spectrum of this source.
j-Colla et al. (1975).
k-Marcha et al. (1996).
l-Subtracted $90\pm7$ mJy background source at RA 19 18 17.1, Dec 51 37 53.
m-Subtracted $26 \pm 1$ mJy background source at RA 19 18 17.1, Dec 51 37 53.
n-Uncertain redshift.


   
Table A.5: The measured wavelengths and resulting redshifts of the most prominent emission and absorption lines. Column 1 gives the name of the source, Col. 2 the used line, Col. 3 the measured wavelength, i.e. the position of the peak of the Gaussian used in fitting the line, and Col. 4 the therefrom derived redshift of that line. The last line for each source gives the average redshift.
(1) (2) (3) (4)
Source Line $\lambda_{\rm peak}/[$Å] Redshift
B0211+326 [O II]3727 4697.04 0.2603
  [Ne III] 4877.16 0.2606
  H$\beta$ 6127.18 0.2605
  [O III]4959 6250.79 0.2605
  [O III]5007 6311.32 0.2605
      0.2605$\,\pm\,$0.0002
B0217+367 Ca II3934 4078.60 0.0368
  Ca II3968 4115.06 0.0371
  G-band 4462.41 0.0366
  Mg-b 5364.99 0.0367
  Na D 6110.44 0.0369
      0.0368$\,\pm\,$0.0003
B0648+733 G-band 4798.18 0.1146
  H$\beta$ 5417.93 0.1146
  [O III]4959 5527.37 0.1146
  [O III]5007 5580.97 0.1146
  Mg-b 5766.97 0.1144
  [O I]6300 7020.84 0.1144
  [N II]6583 7336.42 0.1144
      0.1145$\,\pm\,$0.0002
B0648+431 G-band 4688.06 0.0890
  Mg-b 5636.05 0.0891
  Na D 6418.92 0.0892
      0.0891$\,\pm\,$0.0002
B0658+490 Mg-b 5511.23 0.0650
  Na D 6275.81 0.0650
  [N II]6583 7010.76 0.0650
      0.0650$\,\pm\,$0.0002
B0747+426a [O II]3727 4483.93 0.2031
  Ca II3934 4731.23 0.2027
  Ca II3968 4772.31 0.2027
  G-band 5178.74 0.2030
  Mg-b 6228.69 0.2036
      0.2030$\,\pm\,$0.0004
B0750+434 [Ne V]3426 4615.94 0.3473
  [O II]3727 5022.40 0.3476
  [Ne III]3869 5211.82 0.3471
  [O III]4363 5879.17 0.3475
  H$\beta$ 6550.15 0.3475
  [O III]4959 6681.97 0.3474
  [O III]5007 6746.39 0.3474
      0.3474$\,\pm\,$0.0003


(1) (2) (3) (4)
Source Line $\lambda_{\rm peak}/[$Å] Redshift
B0757+472 H$\gamma$ 5019.76 0.1566
  H$\beta$ 5622.10 0.1566
  [O III]4959 5736.78 0.1568
  [O III]5007 5792.23 0.1568
      0.1567$\,\pm\,$0.0002
B0801+741 H$\beta$ 5446.74 0.1205
  [O III]5007 5610.22 0.1205
  Na D 6603.31 0.1205
  [O I]6300 7058.78 0.1204
  H$\alpha$ 7351.97 0.1202
  [S II]6583 7524.50 0.1204
      0.1204$\,\pm\,$0.0002
B0809+454 [O II]3727 4548.56 0.2204
  H$\beta$ 5933.56 0.2206
  [O III]4959 6052.08 0.2204
  [O III]5007 6109.84 0.2203
  H$\alpha$ 8007.07 0.2200
      0.2204$\,\pm\,$0.0003
B0813+758 [O II]3727 4591.00 0.2318
  H$\beta$ 5989.61 0.2322
  [O III]4959 6111.66 0.2324
  [O III]5007 6170.54 0.2324
  [O I]6300 7766.57 0.2328
  H$\alpha$ 8089.26 0.2326
      0.2324$\,\pm\,$0.0003
B0905+352 [N II]6548 7242.29 0.1059
  [N II]6583 7279.51 0.1058
      0.106$\,\pm\,$0.001
or      
  G-band 5422.53 0.2596
  Mg-b 6512.59 0.2585
      0.260$\,\pm\,$0.002
B0935+743 Ca II3968 4448.92 0.1212
  Mg-b 5806.05 0.1219
  Na D 6608.56 0.1214
      0.1215$\,\pm\,$0.0003
B1029+281 H$\beta$ 5274.68 0.0851
  [O III]4959 5382.18 0.0853
  [O III]5007 5434.69 0.0854
  Mg-b 5618.53 0.0857
  Na D 6397.44 0.0856
  [O I]6300 6837.35 0.0853
  H$\alpha$ 7121.47 0.0851
      0.0854$\,\pm\,$0.0002
B1044+745a Ca II3968 4448.36 0.1211
  Mg-b 5800.85 0.1209
  Na D 6606.56 0.1211
      0.1210$\,\pm\,$0.0003


 
Table A.5: continued.
(1) (2) (3) (4)
Source Line $\lambda_{\rm peak}/[$Å] Redshift
B1110+405 G-band 4625.03 0.0743
  Na D 6332.42 0.0746
  [N II]6583 7073.81 0.0746
      0.0745$\,\pm\,$0.0003
B1213+422 [O II]3727 4632.22 0.2429
  [Ne III]3869 4806.84 0.2424
  [O III]4363 5422.13 0.2428
  H$\beta$ 6041.38 0.2428
  [O III]4959 6162.09 0.2426
  [O III]5007 6221.83 0.2426
  [O I]6300 7828.06 0.2425
  H$\alpha$ 8154.30 0.2425
      0.2426$\,\pm\,$0.0002
B1306+621a Ca II3934 4574.07 0.1627
  Ca II3968 4612.79 0.1625
  G-band 5003.63 0.1623
  Mg-b 6016.99 0.1627
      0.1625$\,\pm\,$0.0004
B1310+451 Ca II3934 4075.03 0.0358
  Ca II3968 4110.96 0.0360
  G-band 4458.96 0.0358
  Mg-b 5359.83 0.0357
  Na D 6102.51 0.0356
  [N II]6583 6817.81 0.0357
      0.0358$\,\pm\,$0.0002
B1416+380 Mg-b 5874.33 0.1351
  Na D 6688.00 0.1349
  [O I]6300 7150.68 0.1350
  H$\alpha$ 7448.93 0.1350
  [N II]6583 7471.70 0.1350
      0.1350$\,\pm\,$0.0002
B1426+295 G-band 4678.63 0.0868
  [O III]4363 4742.83 0.0871
  H$\beta$ 5283.63 0.0869
  Mg-b 5627.45 0.0874
  Na D 6403.01 0.0865
  [N II]6583 7156.50 0.0871
      0.0870$\,\pm\,$0.0003



 
(1) (2) (3) (4)
Source Line $\lambda_{\rm peak}/[$Å] Redshift
B1543+845a [O III]4959 5955.22 0.2009
  [O III]5007 6013.78 0.2011
      0.201$\,\pm\,$0.001
B1709+464 Ca II3968 4114.19 0.0368
  G-band 4463.67 0.0369
  Mg-b 5366.13 0.0369
  Na D 6108.30 0.0365
  [N II]6583 6824.31 0.0367
      0.0368$\,\pm\,$0.0002
B1736+375 Ca II3968 4548.75 0.1563
  Mg-b 5984.90 0.1565
  Na D 6811.76 0.1559
      0.1562$\,\pm\,$0.0003
B1852+507 G-band 4717.29 0.0958
  Mg-b 5670.70 0.0958
  Na D 6457.09 0.0957
      0.0958$\,\pm\,$0.0003
B1911+470 G-band 4540.16 0.0546
  Mg-b 5457.87 0.0547
  Na D 6216.32 0.0549
  [N II]6583 6944.73 0.0549
      0.0548$\,\pm\,$0.0002
B1918+512 Ca II3968 5050.42 0.2838
  [O III]5007 6425.44 0.2833
      0.284$\,\pm\,$0.001
B2147+816 [O II]3727 4270.15 0.1457
  [Ne III]3869 4432.08 0.1455
  H$\gamma$ 4972.15 0.1457
  [O III]4363 4998.67 0.1457
  H$\beta$ 5568.67 0.1456
  [O III]4959 5681.59 0.1457
  [O III]5007 5736.42 0.1457
      0.1457$\,\pm\,$0.0001


Notes:
a-Spectrum has been smoothed with a 3 pixel rectangular box.



  
Table A.6: The flux density levels of the first contour in the presented radio contour maps. Column 1 gives the name of the source; Cols. 2 to 5 give the flux density of the first contour in the radio contour plots of the WENSS, NVSS, FIRST and WSRT radio map. Column 6 gives the beam size of the WSRT beam in cases where a WSRT radio map is presented. Column 7 gives the origin of the presented optical images. Here, PI stands for POSS-I, PII for POSS-II; LDSS is an imaging spectrograph on the 4.2-m WHT on La Palma, HARIS is an imaging spectrograph on the 2.2-m University of Hawaii telescope on Mauna Kea. Unless indicated otherwise, contour levels have been plotted at -1,1,2,4,8,16,32,64,128,256 times the flux density level presented in this table.


\begin{displaymath}\begin{tabular}{l c l l l l@{$\,\times\,$}r l} \hline \hline... ...3 & & & \multicolumn{2}{c}{\ } & PII \\ \hline % \end{tabular}\end{displaymath}


Notes:
a-Extra contour plotted at a level of $\sqrt2$ times the lowest contour level.



  \begin{figure} {\resizebox{167mm}{!}{\epsfig{file=hh.eps,angle=0}} } % \end{figure} Figure A.1: B0211+326: The WENSS radio contour plot, an overlay of the WSRT radio map (contours) with an optical image (grey scale; the identification has been encircled) and the optical spectrum of the host galaxy.


  \begin{figure} \par {\resizebox{16.4cm}{!}{\epsfig{file=DS1923.A2,angle=0}} } % \end{figure} Figure A.2: B0217+367: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the WSRT radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=11.9cm,clip]{DS1923.A3} \end{figure} Figure A.3: B0648+733: The WENSS (left) and NVSS (right) radio contour plots, an overlay of the WSRT radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \includegraphics[width=8cm,clip]{DS1923.A4} \end{figure} Figure A.4: B0648+431: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the WSRT radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} {\resizebox{!}{17.3cm}{\epsfig{file=DS1923.A5,angle=0}} } %\end{figure} Figure A.5: B0658+490: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the WSRT radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=13.6cm,clip]{DS1923.A6} \end{figure} Figure A.6: B0747+426: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale; the identification has been encircled) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=11.2cm,clip]{DS1923.A7} \end{figure} Figure A.7: B0750+434: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=13.8cm,clip]{DS1923.A8} \end{figure} Figure A.8: B0757+477: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\resizebox{!}{16.5cm}{\epsfig{file=DS1923.A9,angle=0}} \end{figure} Figure A.9: B0801+741: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the WSRT radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=13.7cm,clip]{DS1923.A10} \end{figure} Figure A.10: B0809+454: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=14.6cm,clip]{DS1923.A11} \end{figure} Figure A.11: B0813+758: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the WSRT radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=13.7cm,clip]{DS1923.A12} \end{figure} Figure A.12: B0905+352: The WENSS radio contour plot, an overlay of the FIRST radio map (contours) with an optical image (grey scale; the identification has been encircled) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=12.6cm,clip]{DS1923.A13} \end{figure} Figure A.13: B0935+352: The WENSS radio contour plot, an overlay of the NVSS radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=12.6cm,clip]{DS1923.A14} \end{figure} Figure A.14: B1029+281: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=15.7cm,clip]{DS1923.A15} \end{figure} Figure A.15: B1044+745: The WENSS radio contour plot, an overlay of the NVSS radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=15.2cm,clip]{DS1923.A16} \end{figure} Figure A.16: B1110+405: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=14cm,clip]{DS1923.A17} \end{figure} Figure A.17: B1213+422: The WENSS radio contour plot, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=17.5cm,clip]{DS1923.A18} \end{figure} Figure A.18: B1245+676: The WENSS radio contour plot and an overlay of the NVSS radio map (contours) with an optical image (grey scale). An optical spectrum has been published by Marcha et al. (1996).


  \begin{figure} \par\includegraphics[width=13.8cm,clip]{DS1923.A19} \end{figure} Figure A.19: B1306+621: The WENSS (left) and NVSS (right) radio contour plots, an overlay of the WSRT radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=15cm,clip]{DS1923.A20} \end{figure} Figure A.20: B1310+451: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=15.6cm,clip]{DS1923.A21} \end{figure} Figure A.21: B1416+380: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=13.2cm,clip]{DS1923.A22} \end{figure} Figure A.22: B1426+295: The WENSS (left) and NVSS (right) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=14.4cm,clip]{DS1923.A23} \end{figure} Figure A.23: B1543+845: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the NVSS radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=15.2cm,clip]{DS1923.A24} \end{figure} Figure A.24: B1709+464: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the FIRST radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=10.9cm,clip]{DS1923.A25} \end{figure} Figure A.25: B1736+375: The WENSS radio contour plot, an overlay of the NVSS radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy of the central source; note the fuzzy optical object near the center of the northern radio component.


  \begin{figure} \par\includegraphics[width=12.9cm,clip]{DS1923.A26} \end{figure} Figure A.26: B1852+507: The WENSS radio contour plot, an overlay of the NVSS radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=14cm,clip]{DS1923.A27} \end{figure} Figure A.27: B1911+470: The WENSS radio contour plot, an overlay of the NVSS radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=14.8cm,clip]{DS1923.A28} \end{figure} Figure A.28: B1918+516: The WENSS radio contour plot, an overlay of the 1.4-GHz WSRT radio map (contours) with an optical image (grey scale; the identification is indicated by the arrow) and the optical spectrum of the host galaxy.


  \begin{figure} \par\includegraphics[width=14.2cm,clip]{DS1923.A29} \end{figure} Figure A.29: B2147+816: The WENSS (upper) and NVSS (lower) radio contour plots, an overlay of the NVSS radio map (contours) with an optical image (grey scale) and the optical spectrum of the host galaxy.

Copyright ESO 2001