Abstract

We present some first results on the variability, polarization and general properties of radio sources selected at 20 GHz, the highest frequency at which a sensitive radio survey has been carried out over a large area of sky. Sources with flux densities above 100 mJy in the Australia Telescope Compact Array 20 GHz pilot survey at declination −60° to −70° were observed at up to three epochs during 2002–04, including near-simultaneous measurements at 5, 8 and 18 GHz in 2003. Of the 173 sources detected, 65 per cent are candidate QSOs or BL Lac objects, 20 per cent galaxies and 15 per cent faint (bJ > 22 mag) optical objects or blank fields.

On a 1–2 yr time-scale, the general level of variability at 20 GHz appears to be low. For the 108 sources with good-quality measurements in both 2003 and 2004, the median variability index at 20 GHz was 6.9 per cent and only five sources varied by more than 30 per cent in flux density.

Most sources in our sample show low levels of linear polarization (typically 1–5 per cent), with a median fractional polarization of 2.3 per cent at 20 GHz. There is a trend for fainter 20 GHz sources to have higher fractional polarization.

At least 40 per cent of sources selected at 20 GHz have strong spectral curvature over the frequency range 1–20 GHz. We use a radio ‘two-colour diagram’ to characterize the radio spectra of our sample, and confirm that the flux densities of radio sources at 20 GHz (which are also the foreground point-source population for cosmic microwave background anisotropy experiments like Wilkinson Microwave Anisotropy Probe and Planck) cannot be reliably predicted by extrapolating from surveys at lower frequencies. As a result, direct selection at 20 GHz appears to be a more efficient way of identifying 90 GHz phase calibrators for Atacama Large Millimeter Array (ALMA) than the currently proposed technique of extrapolation from radio surveys at 1–5 GHz.

1 INTRODUCTION

Most large-area radio imaging surveys have been carried out at frequencies of 1.4 GHz or below, where the long-term variability of the radio-source population is generally low. The catalogued flux densities measured by such surveys can therefore continue to be used with a high level of confidence for many years after the survey was made.

It is not clear to what extent this is true for radio surveys carried out at higher frequencies, where the source population becomes increasingly dominated by compact, flat-spectrum sources which may be variable on time-scales of a few years.

We are currently carrying out a sensitive radio survey of the entire southern sky at 20 GHz, using a wide-band analogue correlator on the Australia Telescope Compact Array (ATCA; see Ricci et al. 2004a, for an outline of the pilot study for this survey). We have therefore begun an investigation of the long-term variability of radio sources selected at 20 GHz, which will also help us estimate the likely long-term stability of our source catalogue.

There is little information to guide us in what to expect. Only a few studies of radio-source variability have been carried out at frequencies above 5 GHz and these have generally targeted sources which were either known to be variable at lower frequencies, or were selected to have flat or rising radio spectra at frequencies below about 5 GHz. Such objects may not be typical of the 20 GHz source population as a whole.

The full AT 20 GHz (AT20G) survey, using the whole 8 GHz bandwidth of the analogue correlator and coherently combining all three interferometer baselines, began in late 2004 and has a detection limit of 40–50 mJy at 20 GHz, i.e. about a factor of 2 fainter than the sources discussed here. It will eventually cover the entire southern sky from declination Dec. 0° to −90°.

Our reasons for carrying out a pilot survey in advance of the full AT20G survey were to characterize the high-frequency radio-source population, and to optimize the observational techniques used in the two-step survey process (i.e. fast scans of large areas of sky with a wide-band analogue correlator, followed by snapshot imaging of candidate detections) to maximize the completeness, reliability and uniformity of the final AT20G catalogue. Because of the slightly different observational techniques used in 2002, 2003 and 2004, the pilot survey data are not as complete or uniform as the AT20G data are intended to be. The pilot survey nevertheless provides an important first look at the faint radio-source population at 20 GHz. Since corrections for extragalactic foreground confusion will be critical for next-generation cosmic microwave background (CMB) surveys, a better knowledge of the properties of high-frequency radio sources (and especially their polarization and variability) is particularly desirable.

This paper presents an analysis of the radio-source population down to a limiting flux density of about 100 mJy at 20 GHz, based on observations in the Dec. zone −60° to −70° scanned by the AT 20 GHz pilot survey in 2002 and 2003. Our aim is to provide some first answers to the following questions.

  • How does the radio-source population at 20 GHz relate to the ‘flat-spectrum’ and ‘steep-spectrum’ populations identified at lower frequencies?

  • What fraction of radio sources selected at 20 GHz are variable on time-scales of a few years, and how stable in time is a 20 GHz source catalogue?

  • What are the polarization properties of radio continuum sources selected at 20 GHz?

2 OBSERVATIONS

2.1 The ATCA wide-band correlator

An analogue correlator with 8 GHz bandwidth (Roberts, Leach & Wilson, in preparation), originally developed for the Taiwanese CMB instrument AMiBA (Lo et al. 2001) is currently being used at the ATCA to carry out a radio continuum survey of the entire southern sky at 20 GHz. The wide bandwidth of this correlator, combined with the fast scanning speed of the ATCA, makes it possible to scan large areas of sky at high sensitivity despite the small (2.3 arcmin) field of view at 20 GHz. Since delay tracking cannot be performed with this wide-band analogue correlator, all scanning observations are carried out on the meridian (where the delay for an east–west interferometer is zero).

The fast-scanning survey measures approximate positions and flux densities for all candidate sources above the detection threshold of the survey. Follow-up 20 GHz imaging of these candidate detections is then carried out a few weeks later, using the ATCA in a hybrid configuration with its standard (delay-tracking) digital correlator. These follow-up images allow us to confirm detections, and to measure accurate positions and flux densities for the detected sources. Finally, the confirmed sources are also imaged at 5 and 8 GHz to measure their radio spectra, polarization and angular size.

2.2 Observations in the −60° to −70° Dec. zone

Tables 1 and 2 summarize the telescope and correlator configurations used for the observations discussed in this paper. There are three main data sets.

Table 1

log of ATCA fast-scanning observations with the wide-band analogue correlator in the Dec. zone −60° to −70°. Nant is the number of antennas used for each scanning session.

Date Nant νcen (GHz) Bandwidth (GHz) Baselines (m) 
2002 September 13–17 18 3.4 30 
2003 October 9–16 17.6, 20.4 6–7 30, 30, 60 
Date Nant νcen (GHz) Bandwidth (GHz) Baselines (m) 
2002 September 13–17 18 3.4 30 
2003 October 9–16 17.6, 20.4 6–7 30, 30, 60 
Table 2

log of follow-up ATCA imaging observations of sources detected in the scanning survey at 20 GHz. Nant shows the number of antennas equipped with 12 mm receivers for each observing session. The angular resolution of the follow-up images is typically 8 arcsec at 4.8 GHz, 4 arcsec at 8.6 GHz and 15 arcsec at 20 GHz.

Date ATCA configuration Observed frequency (GHz) Nant 
2002 October 8–12 H168B 17.2, 18.8 
2003 November 3–6 H214 17.0, 19.0, 21.0, 23.0 
2003 November 8–10 1.5D 4.8, 8.6 
2004 October 21–28 H214 19.0, 21.0 
Date ATCA configuration Observed frequency (GHz) Nant 
2002 October 8–12 H168B 17.2, 18.8 
2003 November 3–6 H214 17.0, 19.0, 21.0, 23.0 
2003 November 8–10 1.5D 4.8, 8.6 
2004 October 21–28 H214 19.0, 21.0 
  • The ATCA pilot survey observations made in 2002 and published by Ricci et al. (2004a). These are briefly described in Section 2.4 below.

  • Data from a resurvey of the same Dec. zone at 20 GHz in 2003, together with near-simultaneous observations at 4.8 and 8.6 GHz of the confirmed sources (see Section 2.5).

  • 20 GHz images made in 2004 of sources detected at 18 GHz in 2002 and/or 2003, as part of a program to monitor the long-term variability of the sources detected in the pilot survey (Section 2.6).

Although our ATCA 20 GHz pilot survey covered the whole sky between Dec. −60° and −70°, only sources with Galactic latitude |b| > 10° are discussed in this paper. While the source population at 2 < |b| < 10° is also dominated by extragalactic objects, it is very difficult to make optical identifications of radio sources close to the Galactic plane because of the high density of foreground stars. Since one aim of this study is to examine the optical properties of high-frequency radio sources, we therefore chose to exclude the small number of extragalactic sources which lay within 10° of the Galactic plane, or within forumla of the centre of the Large Magellanic Cloud (LMC).

2.3 The flux-density scale of the ATCA at 20 GHz

At centimetre wavelengths, the ATCA primary flux calibrator is the radio galaxy PKSB1934−638 (Reynolds 1994). Planets have traditionally been used to set the flux-density scale in the 12 mm (18–25 GHz) band, and the planets Mars and Jupiter were used as primary flux calibrators during the first two years of operation of the ATCA 12-mm receivers in 2002–03. However, the use of planets to set the flux-density scale has some significant disadvantages (Sault 2003) as discussed in the following.

  • Their angular size (4–25 arcsec for Mars and 30–48 arcsec for Jupiter) means that they can be resolved out at 20 GHz on baselines greater than a few hundred metres.

  • Their (northern) location on the ecliptic means that they are visible above the horizon for a much shorter time than a southern source like PKSB1934−38, and shadowing of northern sources can also be a problem in some compact ATCA configurations.

PKSB1934−638 was monitored regularly in the 12 mm band over a six-month period in 2003, using Mars as primary flux calibrator (Sault 2003). These observations showed that the flux density of PKSB1934−638 remained constant (varying by less than ±1 to 2 per cent at 20 GHz), making it suitable for use as a flux calibrator at these high frequencies. From 2004, therefore, PKSB1934−638 was used as the primary flux ATCA calibrator at 20 GHz, whereas Mars was used in our 2002 and 2003 observations.

2.4 2002 observations

2.4.1 Scanning observations

The first observations of the Dec. strip −60° to −70° were made by Ricci et al. (2004a). Using a single analogue correlator with 3 GHz bandwidth and two ATCA antennas on a single 30 m baseline, they detected 123 extragalactic (|b| > 5°) sources at 18 GHz above a limiting flux density of 100 mJy. The 2002 observations did not completely cover the whole −60° to −70° Dec. strip because of technical problems which interrupted some of the fast scanning runs. Fig. 4 of Ricci et al. (2004a) shows the 2002 sky coverage and the missing regions, which are mainly in the right ascension (RA) range 5–8 h. The Dec. −60° to −70° strip was therefore re-observed at 22 GHz in 2003, and full coverage was then achieved. The region overlapped by the 2002 and 2003 observations gives a useful test of the completeness of the scanning survey technique, as discussed in Section 4.

Figure 4

Optical identifications for the 20 GHz radio sources in Table 3. Galaxies and stellar objects (QSO candidates) are shown separately. Only 27 sources (13 per cent of the sample) are unidentified down to bJ < 22 mag.

Figure 4

Optical identifications for the 20 GHz radio sources in Table 3. Galaxies and stellar objects (QSO candidates) are shown separately. Only 27 sources (13 per cent of the sample) are unidentified down to bJ < 22 mag.

2.4.2 Follow-up imaging and flux-density errors

Follow-up synthesis imaging of the candidate sources detected in the 2002 scans was carried out at 18 GHz with the ATCA as described by Ricci et al. (2004a). It is important to note that, because the candidate source positions obtained from the wide-band scans in 2002 were typically accurate to ∼1 arcmin, and the primary beam of the ATCA antennas at 20 GHz is only ∼2.3 arcmin, about 30 per cent of the sources detected in the follow-up images were offset by 80 arcsec or more from the pointing centre, and so required large (more than a factor of 2) corrections to their observed flux densities to correct for the attenuation of the primary beam. These corrections were made by Ricci et al. (2004a), but were not explicitly discussed in their paper. It has subsequently become clear that uncertainties in the primary beam correction at very large offsets from the field centre can sometimes introduce large systematic errors into the observed fluxes. For this reason, we now regard the 18 GHz flux-density measurements listed by Ricci et al. (2004a) as unreliable for sources observed at more than 80 arcsec from the imaging field centre. For follow-up imaging in 2003 and subsequent years, sources more than 80 arcsec from the imaging field centre were re-observed at the correct position whenever possible.

2.5 2003 observations

2.5.1 Scanning observations

In 2003, we used three analogue correlators and three ATCA antennas, giving us three independent baselines (of 30, 30 and 60 m). The correlators also had a new design with the potential for 8 GHz operation (Roberts et al. in preparation). The 2003 fast scans were carried out using three ATCA antennas separated by 30 m on an east–west baseline, and scanned in a trellis pattern at 15 deg min−1 with 11° scans from Dec. forumla to forumla, interleaved with 2.3 arcmin separation and sampled at 54 ms.

The system temperature was continually monitored at 17.6 and 20.4 GHz and periods with high sky noise (i.e. due to clouds or rain) were flagged out and repeated later. Calibration sources were observed approximately once per day by tracking them through transit (±5 min).

Due to an unforeseen problem matching the wide-band receiver output to the fibre modulator, there was a 15 db slope across the bandpass. When we transformed the 16 lag channels observed into eight complex frequency channels, the resulting bandpass was uncalibratable and unphysical. This occurred because we had an analogue correlator and there is no exact Fourier transform relation between delay and frequency (Harris & Zmuidzinas 2001).

The actual bandpass was measured by taking the Fourier transform of the time sequence obtained while tracking a calibrator source through transit. In this case, we have a physical delay which changes as the earth rotates and we can get a sensible bandpass. In the end only two channels were usable, giving a total band width of 3 GHz. It was also impractical to make a phase calibration of the three interferometers with this data. As a result the sensitivity in 2003 was only marginally better than that in 2002, and overlapping scans could not be combined coherently.

To extract a candidate source list from the 2003 raster scans, the correlator delays were cross-matched with the template delay pattern of a strong calibrator. The correlator coefficient for each time stamp along the scans was recorded, and values from overlapping scans were incoherently combined to form images in 12 equal-area zenithal projection maps (each 2h wide in RA). The source finding algorithm imsad implemented in miriad was used to extract candidate sources above a 5σ threshold.

2.5.2 Follow-up imaging

A list of 1350 candidate sources detected in the scanning survey was observed at 17, 19, 21 and 23 GHz as noted in Table 2. As in 2002, the planet Mars was used as the primary flux calibrator. In the 2003 follow-up imaging, the data were reduced as the observations progressed, and sources which were more than 80 arcsec from the imaging centre were re-observed if possible. This significantly improved the accuracy of the flux-density measurements for the 2003 images compared to those made in 2002, as can be seen in Fig. 1.

Figure 1

Comparison of the 18 GHz flux densities measured in 2002 and 2003 for sources detected independently in the scanning process. Sources which were detected in 2002 but not recovered in 2003 are shown as open triangles with a flux-density limit of 100 mJy for 2003. As discussed in the text, the error bars on the 2002 flux-density measurements are significantly larger than for 2003. Open squares show sources with offsets of more than 80 arcsec from the imaging field centre in the 2002 data.

Figure 1

Comparison of the 18 GHz flux densities measured in 2002 and 2003 for sources detected independently in the scanning process. Sources which were detected in 2002 but not recovered in 2003 are shown as open triangles with a flux-density limit of 100 mJy for 2003. As discussed in the text, the error bars on the 2002 flux-density measurements are significantly larger than for 2003. Open squares show sources with offsets of more than 80 arcsec from the imaging field centre in the 2002 data.

Images of each follow-up field were made at 18 and 22 GHz using the multifrequency synthesis (MFS) technique. (Conway, Cornwell & Wilkinson 1990; Sault & Wieringa 1994). Since the signal-to-noise ratio (S/N) in the 18 GHz band was significantly higher than at 22 GHz, we used only the 18 GHz data in our subsequent analysis. The median rms noise in the follow-up images was 1.5 mJy beam−1 at 18 GHz, and sources stronger than five times the rms noise level (estimated from the V-Stokes images) were considered to be genuine detections. The 364 sources with confirmed detections at 18 GHz (including some Galactic plane sources) were imaged at 5 and 8.6 GHz in 2003 November. The total integration time for these follow-up images was 80 s (two cuts) at 17–19 and 21–23 GHz, and 180 s (six cuts) at 5 and 8 GHz.

2.6 2004 observations

A sample of 200 sources detected at 18 GHz in 2002 and/or 2003 was re-imaged on 2004 October 22 in a series of targeted observations at 19 and 21 GHz, using the ATCA hybrid configuration H214. All these imaging observations were centred at the source position measured in 2002/2003, so that positional offsets from the imaging field centre were negligible. The 19 and 21 GHz data were combined to produce a single 20 GHz image of each target source. The total integration time at 20 GHz was 240 s (two cuts), and the median rms noise in the final images was 0.7 mJy.

3 DATA REDUCTION AND SOURCE FITTING

3.1 Reduction of the follow-up images

For the 2003 data, deconvolved images of the confirmed sources were made at 5, 8 and 18 GHz and positions and peak flux densities were measured using the miriad task maxfit, which is optimum for a point source. We also used the miriad task imfit to measure the integrated flux density and angular extent of extended sources. Where necessary, the fitted flux densities were then corrected for the primary beam attenuation at frequencies between 17 and 23 GHz based on a polynomial model of the Compact Array antenna pattern.

Positional errors were estimated by quadratically adding a systematic term and a noise term: the systematic term was assessed by cross-matching the 18 GHz source positions with the Ma et al. (1998) International Coordinate Reference Frame source positions; the noise term is calculated from the synthesized beam size divided by the flux S/N. The median position errors are forumla in RA and forumla in Dec.

To estimate the flux-density errors, we quadratically added the rms noise from V-Stokes images to a multiplicative gain error estimated from the scatter between snapshot observations of the strongest sources. The median percentage gain errors were 2 per cent at 5 and 8 GHz, and 5 per cent at 18 GHz.

For the 2004 data, the 19 and 21 GHz visibilities were amplitude and phase calibrated in miriad. As noted in Section 2.3, PKSB1934−638 was used as the primary flux calibrator. The calibrated visibilities were combined to form 20 GHz images using the MFS technique and peak fluxes were worked out using the miriad task maxfit. Position and flux errors were determined in the same way as for the 2003 data (see Fig. 2).

Figure 2

Comparison of 18 GHz flux densities measured in 2002 and 2003 with 20 GHz flux densities measured in 2004. The horizontal dotted line shows the sensitivity limit of the 2002 and 2003 surveys.

Figure 2

Comparison of 18 GHz flux densities measured in 2002 and 2003 with 20 GHz flux densities measured in 2004. The horizontal dotted line shows the sensitivity limit of the 2002 and 2003 surveys.

3.2 Polarization measurements

As all four Stokes parameters were available, linear polarization measurements were carried out on the 2003 and 2004 data. Q-Stokes, U-Stokes and polarized flux forumla were calculated at the peak of the total intensity emission at 20 GHz. The rms in the V-Stokes image for each source was used as an estimate of the noise in U and Q. This error estimate is then used to correct to first order for the Rician bias in P (Leahy 1989) and to set the 3σ lower limit on P. Note that this estimate corresponds to the integrated polarization for unresolved sources but is only the polarization at the peak in I for resolved sources. Since over 95 per cent of the sources in our sample are unresolved at 20 GHz (see Section 3.4), this is not a serious problem.

Although the measurements of fractional linear polarization made in 2003 and 2004 were in good general agreement, the 2004 measurements had lower error bars and detected fractional polarizations as low as 1–2 per cent, whereas the 2003 measurements detected only the most highly polarized sources with typical fractional polarizations of 4–5 per cent or higher. We therefore use only the 2004 data in the analysis in Section 8.2 of this paper. A more detailed analysis of extended sources, and of the linear polarized flux and position angle (PA) at 5, 8 and 20 GHz will be presented in a later paper.

Fig. 3 compares our measurements of fractional linear polarization with those made by Ricci et al. (2004b) at 18.5 GHz for objects in common. We find a systematic difference of about 1 per cent in the two data sets, and have investigated this in consultation with authors of the Ricci et al. (2004b) paper. We find that the Ricci et al. (2004b) polarization values are about 1 per cent too high because these observers used a triple correlation method to measure polarized flux (poor phase stability during their run meant that they were not able to produce calibrated images) and did not remove the polarization bias from their data. We estimate that the polarization bias in the Ricci et al. (2004b) data contributes roughly 10 mJy of spurious flux to their polarization measurements. Since their sources have typical 18 GHz flux densities of ∼1 Jy, this corresponds to a ∼1 per cent increase in the measured fractional polarization compared to the true value.

Figure 3

Comparison of the fractional linear polarization measured at 20 GHz in this paper with the value measured at 18.5 GHz by Ricci et al. (2004b) for sources in common. Filled circles show objects with polarization detected in both studies, and open triangles show upper limits.

Figure 3

Comparison of the fractional linear polarization measured at 20 GHz in this paper with the value measured at 18.5 GHz by Ricci et al. (2004b) for sources in common. Filled circles show objects with polarization detected in both studies, and open triangles show upper limits.

3.3 The combined 20 GHz sample 2002–04

Table 3 presents the observed flux densities (in mJy) for extragalactic sources with flux densities above 100 mJy at 20 GHz. As noted in Section 2.2, sources which have low Galactic latitude (|b| < 10°), or lie within forumla of the centre of the LMC, have been excluded. A few sources with measured flux densities consistently less than 100 mJy in the follow-up images were also omitted from the table. These sources are below the detection limit of the scanning survey and were found by chance in the follow-up images, which cover a much smaller area of sky but reach a detection limit of a few mJy at 20 GHz.

Table 3

Radio spectra and optical IDs for extragalactic 18 GHz sources (|b| > 10°, and excluding objects within forumla of the LMC centre). Sources marked with # in column 1 are resolved doubles in our 18–20 GHz images: for these objects, the position is that of the radio centroid and the flux density is the total for both components.

(1) Name (2) Radio position (J2000) (3) B (mag) (4) T (5) S18 2002 (6) ± (7) S18 2003 (8) ± (9) S20 2004 (10) ± (11) S8 2003 (12) ± (13) S5 2003 (14) ± (15) S843 SUMSS (16) ± (17) Polarization (per cent) (18) ± (19) Variability (per cent) (20) Alternate name (21) Notes 
0007−6113 00 07 20.85 −61 13 06.8 19.92 – – 145 10 150 142 143 87 <2.3 – <6.0 PMNJ0007−6112  
0024−6820 00 24 06.98 −68 20 54.4 17.62 366 14 338 24 256 13 388 471 1250 38 1.7 0.3 12.8 PKS0021−686 MX 
0025−6028# 00 25 15.91 −60 28 27.6 >22 94 19 – – 92 – – – – 1777 69 <7.6 – – PKS0022−60  
0103−6439 01 03 33.93 −64 39 08.0 18.88 290 58 200 14 333 19 215 173 770 69 <1.0 – 22.5 PKS0101−649 
0109−6049 01 09 15.61 −60 49 48.9 22.01 [872] 194 506 35 396 20 699 13 787 14 481 15 0.6 0.2 11.1 PKS0107−610 CQ 
0110−6315 01 10 16.87 −63 15 56.3 20.12 154: 34 278 19 208 10 165 155 178 <1.4 – 13.5 PKS0108−635 QP 
0112−6634 01 12 19.05 −66 34 45.3 17.86 415 92 295 21 348 17 413 474 16 451 49 3.0 0.2 6.5 PKS0110−668 QP 
0113−6753 01 13 11.50 −67 53 03.2 20.86 [127] 28 189 13 241 12 112 108 68 2.7 0.4 11.0 PMNJ0113−6753  
0121−6309# 01 21 40.64 −63 09 02.9 17.63 – – [121] 71 293 418 2650 97 <7.9 – – PKS0119−63 QX z= 0.837 
0144−6421 01 44 16.89 −64 21 42.9 21.35 286 20 172 12 175 201 188 108 4.8 0.6 <6.0 PMNJ0144−6421  
0154−6604 01 54 31.57 −66 04 16.4 18.87 – – 245 17 161 296 390 954 29 4.3 0.5 20.0 PKS0153−663 QP 
0158−6411 01 58 37.00 −64 11 28.4 19.51 133: 30 114 150 132 132 191 4.4 0.6 12.6 PMNJ0158−6411  
0158−6334 01 58 55.11 −63 34 49.7 19.29 [111] 25 119: 90 144 192 559 17 7.0 0.8 – PKS0157−638  
0201−6638 02 01 07.76 −66 38 12.9 20.26 – – 207 14 337 17 246 270 168 2.7 0.2 23.3 PMNJ0201−6638  
0206−6143 02 06 40.01 −61 43 32.4 20.01 – – 236: 17 209 11 205 211 220 3.7 0.2 – PMNJ0206−6143  
0207−6837 02 07 50.94 −68 37 55.0 20.15 – – 244 17 – – 300 332 400 12 – – – PKS0206−688 QP 
0208−6216 02 08 01.18 −62 16 35.6 18.24 158 35 – – 151 – – – – 193 <1.5 – – PMNJ0207−6216  
0214−7027 02 14 04.60 −70 27 06.3 19.35 [149] 33 – – 385 19 – – – – 108 1.0 0.2 – PMNJ0214−7027  
0214−6149 02 14 16.25 −61 49 33.8 20.33 248 55 316: 22 423 21 220 217 212 2.0 0.1 – PKS0212−620  
0219−6806 02 19 41.77 −68 06 18.2 20.08 – – 226: 16 170 221 279 729 22 1.3 0.4 – PKS0218−683 
0220−6330 02 20 54.20 −63 30 19.6 19.11 – – 367 26 367 18 333 363 368 11 2.0 0.2 <6.0 PKS0219−637 QP 
0230−6214 02 30 11.60 −62 14 35.5 19.20 – – 146 10 159 85 93 100 <1.0 – <6.0 PMNJ0230−6214  
0236−6136 02 36 53.25 −61 36 15.1 18.18 [511] 113 394 28 522 26 338 338 604 18 4.4 0.1 13.0 PKS0235−618 CQXP 
0247−6325 02 47 11.06 −63 25 38.3 17.87 – – 154 11 110 80 44 12 <1.8 – 15.9  
0250−6355 02 50 36.23 −63 55 01.6 19.67 – – 147 10 190 10 162 158 109 4.2 0.3 11.7 PMNJ0250−6355  
0251−6000 02 51 26.27 −60 00 06.3 19.78 – – 286 20 308 15 395 402 274 8.6 0.2 <6.0 PKS0250−602 QP 
0257−6112# 02 57 36.36 −61 12 30.4 18.78 – – 79 101 128 150 382 12 <2.3 – – PKS0256−614  
0303−6458 03 03 50.57 −64 58 54.5 >22 149 33 171 12 131 156 146 48 <1.5 – 12.2 PMNJ0303−6458 
0303−6211 03 03 50.67 −62 11 25.2 19.48 [2202] 489 1330 93 1256 63 1941 37 2181 40 2513 75 2.5 0.1 <6.0 PKS0302−623 CQXWV* 
0304−7007 03 04 18.26 −70 07 41.4 19.09 – – 190 13 160 271 311 238 3.7 0.4 6.9 PKS0304−703  
0309−6058 03 09 56.13 −60 58 38.9 19.00 – – 1207 84 1152 58 1244 24 1348 24 993 30 0.8 0.1 <6.0 PKS0308−611 CQWVP* 
0314−6548 03 14 22.44 −65 48 24.7 19.06 297 66 277 19 274 14 164 161 354 11 3.0 0.2 <6.0 PKS0313−660 QX z= 0.636 
0323−6026 03 23 08.44 −60 26 31.3 20.69 159: 35 263 18 222 11 220 223 199 2.2 0.2 6.8 PMNJ0323−6026  
0340−6811 03 40 06.53 −68 11 26.1 22.01 – – 200: 14 128 207 10 160 225 3.7 0.5 – PKS0339−683  
0340−6703 03 40 28.27 −67 03 16.6 19.24 [177] 39 256: 18 249 12 222 210 374 11 <0.8 – – PMNJ0340−6703  
0341−5954 03 41 21.60 −59 54 08.6 18.21 147 33 177 12 125 195 212 379 11 <2.0 – 16.4 PKS0340−600 
0355−6645 03 55 47.86 −66 45 33.9 19.00 – – 293 21 334 17 483 581 11 1403 42 1.6 0.2 <6.0 PKS0355−66 CQP 
0357−6948 03 57 30.07 −69 48 45.6 >22 [231] 51 – – 111 – – – – 148 <1.9 – – PMNJ0357−6948  
0408−6545 04 08 20.33 −65 45 08.7 >22 543 121 428 30 419 21 1540 30 3188 58 25029 751 3.6 0.2 <6.0 PKS0408−65 C* 
0420−6223 04 20 56.09 −62 23 38.6 >22 – – 188 13 179 482 896 16 5622 169 2.1 0.3 <6.0 PKS0420−62 
0421−6729 04 21 19.71 −67 29 01.6 20.16 – – 127 134 10 124 79 39 <1.4 – <6.0  
0422−6507 04 22 29.15 −65 07 05.0 20.42 [108] 24 – – 103 – – – – 177 2.1 0.6 – PMNJ0422−6507  
0425−6646 04 25 06.77 −66 46 49.8 20.59 [242] 54 236 17 218 11 315 361 91 2.4 0.3 <6.0 PKS0425−669  
0428−6438 04 28 10.87 −64 38 22.6 21.63 180 40 189 13 335 17 168 140 78 <0.7 – 27.4 PMNJ0428−6438  
0433−6030 04 33 34.08 −60 30 13.1 19.10 359: 80 356 25 315 16 324 325 414 13 2.0 0.2 <6.0 PKS0432−606 QP 
0436−6056 04 36 21.77 −60 56 37.3 21.85 – – [491] 44 116 – – – – 136 3.7 0.6 –  
0436−5931 04 36 51.52 −59 31 36.6 15.53 – – 149: 10 77 114 125 96 <2.3 – – ESO118−IG32 
0449−6106 04 49 24.33 −61 06 26.4 >22 – – 172 12 192 10 237 256 427 13 3.9 0.3 <6.0 PKS0448−611  
0504−6049 05 04 01.65 −60 49 52.5 19.43 [116] 26 [272] 19 168 – – – – 568 17 <1.2 – – PKS0503−608 QP 
0505−6215 05 05 46.75 −62 15 44.8 19.42 157 35 [287] 20 86 – – – – 54 <2.1 – – PMNJ0505−6215  
0505−6236 05 05 48.53 −62 36 11.0 20.80 152 34 [201] 16 87 – – – – 110 2.9 0.7 – PMNJ0505−6236  
0506−6109 05 06 43.96 −61 09 41.0 17.16 – – 1883 131 1819 91 1756 34 1791 33 3102 93 1.2 0.1 <6.0 PKS0506−61 QXWE*z= 1.093 
0507−6104 05 07 54.62 −61 04 43.2 21.18 – – 232 16 443 22 336 420 842 25 0.6 0.2 30.8 MRC0507−611  
0516−6207 05 16 44.89 −62 07 05.4 21.20 [530] 118 545: 38 785 39 414 416 418 13 2.8 0.1 –. PKS0516−621 QP 
0522−6107 05 22 34.39 −61 07 57.2 18.46 [1101] 244 462 32 425 21 654 13 700 13 741 22 0.8 0.2 <6.0 PKS0522−611 CQXP z= 1.400 
0534−6106 05 34 35.73 −61 06 07.0 19.29 513 47 503 35 426 30 435 491 451 14 1.6 0.2 6.6 PKS0534−611 QP 
0546−6415 05 46 41.83 −64 15 22.1 16.54 – – 227 16 363 21 189 243 119 <0.6 – 22.5 PMNJ0546−6415 QXW z= 0.323 
0607−6031 06 07 55.13 −60 31 52.0 19.50 – – 161 11 256 13 286 406 1416 43 1.7 0.2 26.1 PKS0607−605 
0610−6058 06 10 30.36 −60 58 37.8 20.15 – – 145: 10 130 186 215 350 11 2.9 0.4 – PKS0609−609 QX 
0620−6107 06 20 05.24 −61 07 31.6 19.99 – – 167 12 235 12 255 287 357 11 10.0 0.3 16.1  
0621−5935 06 21 53.13 −59 35 08.6 19.68 – – 222 16 237 12 396 547 10 1276 38 0.8 0.2 <6.0 PKS0621−595  
0623−6436 06 23 07.75 −64 36 20.7 17.06 – – 481 34 1222 61 368 312 326 13 0.5 0.1 43.2 PMNJ0623−6436 XMI z= 0.1289 
0625−6020 06 25 24.32 −60 20 29.8 >22 – – 269 19 351 18 342 365 288 <0.6 – 12.2 PMNJ0625−6020  
0628−6248 06 28 57.54 −62 48 45.0 21.24 – – 327 23 359 18 396 426 522 16 7.1 0.2 <6.0 PKS0628−627 
0644−6712 06 44 28.15 −67 12 57.6 21.53 – – 230 16 368 18 225 233 218 6.6 0.2 22.5 PKS0644−671 
0647−6058 06 47 40.86 −60 58 05.3 >22 – – 145: 10 97 93 98 108 2.4 0.5 – PMNJ0647−6058  
0650−6510 06 50 57.62 −65 10 12.3 18.69 – – 91 97 174 207 71 3.6 0.6 <6.0 PMNJ0650−6509  
0700−6610 07 00 31.16 −66 10 45.2 15.77 – – 235 16 306 15 293 298 288 3.0 0.2 12.1 PKS0700−661 QP 
0715−6829 07 15 09.51 −68 29 58.2 – – – – 209 15 327 16 236 239 143 6.0 0.2 21.4 PMNJ0715−6829  
0716−6240 07 16 33.57 −62 40 26.5 20.27 – – 316 22 364 18 226 182 116 2.7 0.2 <6.0 PKS0716−625  
0719−6218 07 19 04.55 −62 18 02.5 20.73 – – 249 17 – – 249 13 282 284 – – – PMNJ0719−6218  
0738−6735 07 38 56.49 −67 35 50.6 19.65 – – 255 18 346 17 396 434 531 16 2.2 0.2 14.3 PKS0738−674 QP z= 1.663 
0743−6726# 07 43 31.60 −67 26 25.8 16.71 – – 1069 214 1360 68 1904 38 2109 42 5638 169 4.8 0.1 – PKS0743−67 QXWVP z= 1.510 
0744−6919 07 44 20.26 −69 19 07.3 21.65 237 53 323 23 363 18 330 322 414 12 2.4 0.2 <6.0 PKS0744−691  
0746−6612 07 46 43.66 −66 12 51.4 19.32 – – [371] 27 168 – – – – 2089 63 12.0 0.4 – PKS0746−660  
0806−6101 08 06 49.26 −61 01 29.8 >22 – – 108 147 175 182 163 3.1 0.6 14.4 PMNJ0806−6101  
0818−6634 08 18 49.39 −66 34 00.4 19.12 – – 111 114 127 96 28 <2.7 – <6.0 PMNJ0818−6634  
0820−6814 08 20 11.23 −68 14 40.8 21.52 – – 193 14 64 156 121 53 <4.2 – 49.9 PMNJ0820−6814  
0835−5953 08 35 28.91 −59 53 11.6 >22 – – 269 19 307 15 194 140 25 0.9 0.2 <6.0 PMNJ0835−5953  
0842−6053 08 42 26.48 −60 53 50.4 19.98 – – 318 22 320 16 376 398 745 22 1.2 0.2 <6.0 PMNJ0842−6053 
0845−6527 08 45 11.29 −65 27 23.8 18.01 [237] 53 260 18 214 11 403 422 18 1.1 0.3 8.3 PMNJ0845−6527  
0846−6313 08 46 35.97 −63 13 34.8 19.34 108 24 – – 73 – – – – 86 4.4 1.0 – PMNJ0846−6313  
0847−6235 08 47 02.95 −62 35 40.8 19.16 – – 117 108 140 149 191 2.7 0.8 <6.0 PMNJ0847−6235  
0901−6636 09 01 15.40 −66 36 33.8 21.38 [230] 51 160 11 165 249 266 193 4.5 0.6 <6.0 PKS0900−664  
0923−6648 09 23 47.51 −66 48 37.9 21.78 – – 150: 11 179 137 123 96 6.4 0.5 – PKS0922−666  
0938−6556 09 38 41.82 −65 56 13.6 18.39 – – 104 – – 140 119 197 <1.7 – – PKS0937−657  
0953−6924 09 53 20.48 −69 24 25.4 18.65 – – 198: 14 103 184 195 170 3.5 0.7 – PKS0952−691 QP 
1533−6837 15 33 34.61 −68 37 19.3 21.63 – – 223 12 285 14 – – – – 285 10 <1.3 – 11.1 PKS1528−684  
1542−6807 15 42 57.32 −68 07 49.8 16.77 – – 125: 16 58 – – – – 243 <5.9 – – PMNJ1543−6808  
1546−6837 15 46 44.52 −68 37 29.3 19.51 [233] 52 131 503 25 – – – – 206 2.8 0.2 58.4 PMNJ1546−6837  
1624−6809 16 24 18.55 −68 09 11.3 17.05 331: 16 570 40 723 36 910 17 1473 27 1046 31 0.6 0.2 10.7 PKS1619−680 CQP*z= 1.360 
1647−6438 16 47 37.91 −64 38 00.2 20.05 614: 136 418 29 462 23 424 557 10 644 19 8.6 0.2 <6.0 MRC1642−645 CVE 
1703−6212 17 03 36.78 −62 12 39.1 18.73 – – 1572 110 1287 64 854 17 1223 22 731 22 0.5 0.1 8.6 MRC1659−621 CWE 
1703−6511 17 03 50.56 −65 11 06.2 18.10 [99] 22 – – 135 – – – – 345 10 2.2 0.6 – PKS1658−651  
1709−6905 17 09 55.80 −69 05 22.6 20.34 – – 122 148 70 86 56 <2.1 – 8.2 PMNJ1709−6905  
1721−6154 17 21 39.07 −61 54 42.8 18.91 [340] 75 381 27 297 15 288 285 310 2.5 0.3 11.3 PMNJ1721−6154  
1723−6500 17 23 41.12 −65 00 36.3 13.16 [2945] 654 2671 187 2817 141 2626 51 – – 3724 112 <1.7 – <6.0 NGC6328 CMWVP*z= 0.0142 
1726−6427 17 26 57.91 −64 27 52.4 >22 204 13 209 15 150 344 1041 19 4076 122 <1.8 – 15.6 MRC1722−644 CV 
1735−6215 17 35 08.11 −62 15 21.2 19.59 [256] 57 403 28 300 15 262 403 696 21 1.1 0.3 13.7 MRC1730−622  
1736−5951 17 36 30.95 −59 51 58.3 21.51 236 62 181 13 192 10 151 242 269 2.5 0.4 <6.0 PKS1732−598 
1737−5921 17 37 19.80 −59 21 41.0 20.99 – – 395: 28 247 12 253 368 381 12 5.5 0.3 – PMNJ1737−5921  
1743−6626 17 43 49.13 −66 26 27.5 20.76 176 39 124 192 10 74 117 209 2.7 0.5 20.9 PKS1738−664  
1749−6258 17 49 25.80 −62 58 17.8 19.08 182 40 181 13 186 111 162 244 2.4 0.4 <6.0 PMNJ1749−6258  
1754−6423 17 54 42.21 −64 23 45.3 19.15 83: 18 – – 103 – – – – 177 <2.6 – – PMNJ1754−6423  
1759−5947 17 59 06.08 −59 47 01.1 >22 112 25 – – 67 – – – – 5626 169 13.0 0.9 – PKS1754−59  
1803−6507 18 03 23.58 −65 07 36.8 18.19 [999] 222 1144 80 1314 66 771 19 – – 637 19 0.8 0.1 <6.0 PKS1758−651 CWP 
1807−6413 18 07 54.03 −64 13 50.7 20.56 450 100 – – 277 14 – – – – 94 1.8 0.2 – PMNJ1807−6413  
1807−7012# 18 07 14.76 −70 12 39.9 18.23 131 13 – – 126 – – – – 1199 36 13.2 1.7 – PKS1801−702 
1819−6345 18 19 34.94 −63 45 48.5 16.80 1631 79 – – 1825 91 – – – – 20185 606 0.8 0.1 – PKS1814−63 CMWE*z= 0.0627 
1822−6359# 18 22 14.76 −63 59 24.4 >22 142 28 – – 163 – – – – 4935 181 6.1 0.7 – PKS1817−64  
1824−6717# 18 24 34.21 −67 17 26.1 >22 228 46 – – 310 20 – – – – 3440 134 4.1 0.4 – PKS1819−67  
1836−6649 18 36 59.40 −66 49 08.5 19.54 127 28 – – 146 – – – – 3260 98 4.7 0.4 – PKS1831−668  
1840−6152 18 40 15.43 −61 52 06.3 21.96 245 54 282 20 254 13 – – – – 191 1.1 0.2 <6.0 PKS1835−619  
1844−6808 18 44 11.82 −68 08 05.3 20.00 – – 188 13 114 – – – – 111 2.9 0.6 23.9 PMNJ1844−6808  
1852−6848 18 52 32.29 −68 48 16.1 >22 101: 22 – – 86 – – – – 403 12 4.0 0.6 – PKS1847−688  
1903−6749 19 03 01.32 −67 49 35.5 18.90 419: 21 156 11 481 24 – – – – 232 5.2 0.1 50.7 PMNJ1903−6749  
1906−6556 19 06 47.72 −65 56 41.1 >22 – – [264] 18 111 – – – – 447 14 2.1 0.4 – PKS1901−660  
1913−6950 19 13 31.25 −69 50 37.4 >22 282 63 317 22 192 10 – – – – 34 <0.9 – 24.0  
1916−6928 19 16 36.33 −69 28 33.7 >22 – – 225: 16 117 – – – – 100 3.6 0.4 – PMNJ1916−6928  
1917−6436 19 17 34.06 −64 35 43.8 20.55 – – 116: 64 – – – – 102 6.5 0.7 – PMNJ1917−6435  
1923−6320 19 23 24.64 −63 20 46.2 21.42 – – 184 13 127 – – – – 412 13 1.8 0.4 17.6 PMNJ1923−6320  
1926−6242 19 26 58.09 −62 42 27.6 18.64 133: 30 – – 93 – – – – 139 3.5 0.5 –  
1930−6056 19 30 06.07 −60 56 09.0 20.57 675 150 819 57 572 29 – – – – 696 21 3.1 0.1 17.0 PKS1925−610 CQP 
1933−6942 19 33 31.22 −69 42 58.5 19.94 388 86 – – 259 13 – – – – 744 22 1.2 0.2 – PKS1928−698 QP 
1939−6342 19 39 24.99 −63 42 45.3 18.87 [1272] 350 1227 86 886 44 – – – – 13722 412 <0.2 – <6.0 PKS1934−63 CV*z= 0.183 
1940−6907 19 40 26.09 −69 07 55.1 >22 [568] 126 556 39 442 22 – – – – 1705 51 2.1 0.1 10.3 PKS1935−692 CQV z= 3.154 
1940−6527 19 40 38.91 −65 27 15.7 20.75 – – 242 13 282 14 – – – – 244 0.7 0.2 <6.0 PMNJ1940−6527  
1941−6211 19 41 21.74 −62 11 21.3 21.12 502: 111 390 27 348 17 – – – – 1832 55 4.0 0.2 <6.0 PKS1936−623 QP* 
1942−7015 19 42 45.52 −70 15 44.4 19.29 111 25 – – 75 – – – – 80 2.6 0.7 – PMNJ1942−7015  
2004−6347 20 04 29.52 −63 47 22.7 19.35 456 13 355 25 369 18 369 560 10 749 23 1.5 0.2 <6.0 PMNJ2004−6347 
2015−6712 20 15 00.00 −67 12 58.9 19.02 [73] 16 – – 214 11 – – – – 39 <1.0 – – PMNJ2014−6713 
2017−6824 20 17 29.30 −68 24 54.9 21.99 – – 175 12 164 175 227 243 4.3 0.4 <6.0 PKS2012−685 QP 
2021−6124 20 21 01.34 −61 24 49.2 20.45 183 41 163 11 200 10 321 468 1071 32 4.2 0.3 14.0 PKS2016−615 CQ 
2024−6458 20 24 46.30 −64 58 35.6 20.79 – – [267] 21 192 10 – – – – 126 2.7 0.3 – PMNJ2024−6458  
2027−7007 20 27 24.54 −70 07 17.2 19.19 [308] 68 – – 233 12 – – – – 1041 31 1.7 0.3 – PKS2022−702 Q z= 0.697 
2035−6846 20 35 48.85 −68 46 33.6 19.27 – – 570 40 457 23 651 13 745 14 299 4.2 0.2 9.8 PKS2030−689 QWP 
2035−6602 20 35 51.46 −66 02 07.3 19.24 – – 320 22 259 13 325 386 355 11 3.6 0.2 9.2 PMNJ2035−6602  
2046−6527 20 46 49.64 −65 27 27.4 21.58 116 26 – – 130 – – – – 36 <1.5 – – PMNJ2046−6527  
2048−6804 20 48 23.81 −68 04 51.8 18.20 – – 114 104 122 170 349 11 1.9 0.5 <6.0 PKS2043−682 
2052−6523 20 52 06.64 −65 23 11.3 17.29 – – 275 19 228 11 275 15 375 551 17 1.3 0.3 7.9 PKS2047−655 QP z= 2.320 
2053−6255 20 53 05.62 −62 55 50.9 21.19 – – 236 17 280 14 269 313 171 1.8 0.2 6.9 PMNJ2053−6255  
2059−6745 20 59 09.59 −67 45 23.2 17.70 90 20 – – 104 – – – – 2456 <2.0 – – PMNJ2059−6745 
2106−6547 21 06 59.73 −65 47 44.2 20.88 303 67 315 22 305 15 424 585 11 1555 47 <0.7 – <6.0 PKS2102−659 
2114−6851 21 14 13.46 −68 51 02.4 19.58 140: 31 189 13 223 11 225 285 510 15 2.6 0.3 6.5 PKS2109−690 Q z= 2.910 
2121−6111 21 21 04.10 −61 11 24.2 18.75 214: 48 287 20 357 18 367 476 966 29 2.1 0.2 9.6 MRC2117−614 
2121−6404 21 21 55.05 −64 04 29.8 21.19 – – 263: 18 164 354 588 11 2081 62 <1.1 – – PKS2117−64 
2124−6028 21 24 02.94 −60 28 08.9 17.32 – – [323] 23 134 – – – – 35 <1.5 – –  
2134−6513 21 34 13.25 −65 13 36.9 21.21 – – 166 12 179 136 142 213 6.2 0.4 <6.0 PKS2130−654  
2136−6335 21 36 22.09 −63 35 51.3 19.77 – – 238 17 385 19 180 144 160 0.7 0.2 23.0 PMNJ2136−6335  
2141−6411 21 41 46.50 −64 11 14.8 19.58 – – 200 14 217 11 153 152 176 5.8 0.3 <6.0 PMNJ2141−6411  
2150−6802 21 50 13.43 −68 02 50.6 20.83 215: 48 179 13 246 12 230 229 126 1.0 0.2 14.9 PMNJ2150−6803  
2156−6331 21 56 49.11 −63 31 05.9 19.98 97 22 – – 141 – – – – 57 <1.6 – – PMNJ2156−6331  
2157−6941# 21 57 05.45 −69 41 22.6 13.85 1821 304 [759] 53 1490 75 2760 59 8300 171 41200 1455 2.4 0.1 – ESO075−G41 IXWM z= 0.0283 
2203−6130 22 03 59.63 −61 30 21.9 19.86 249 55 282: 20 289 14 264 346 441 13 3.5 0.2 – PKS2200−617 QP 
2208−6325 22 08 47.15 −63 25 47.6 18.41 [298] 66 335 23 337 17 453 634 12 1429 43 4.2 0.2 <6.0 PKS2204−63 CQ z= 0.618 
2213−6330 22 13 34.73 −63 30 01.5 18.52 325 72 322 23 334 17 223 209 631 25 1.4 0.2 <6.0 PKS2210−637 
2215−6609 22 15 45.26 −66 09 14.0 21.19 110 24 – – 134 – – – – 761 23 4.4 0.5 – PKS2212−664  
2229−6910 22 29 00.21 −69 10 29.8 19.85 – – 596 42 626 31 549 11 491 400 12 0.8 0.1 <6.0 PKS2225−694 QP 
2230−6310 22 30 10.29 −63 10 43.1 19.85 187 42 144 10 156 184 193 231 3.4 0.4 <6.0 PMNJ2230−6310  
2231−6231 22 31 07.91 −62 31 19.2 20.25 [395] 88 316 22 249 12 346 332 267 1.5 0.2 10.7 PKS2227−627  
2243−6250 22 43 07.78 −62 50 57.3 18.19 – – 199 14 224 11 224 194 111 1.2 0.2 <6.0 PKS2239−631 
2254−5926 22 54 56.77 −59 26 00.7 19.80 – – 239: 17 194 10 159 157 159 1.8 0.3 – PKS2251−596 
2256−6533 22 56 24.89 −65 33 25.1 16.90 – – 114 99 125 150 349 10 3.0 0.6 <6.0 PMNJ2256−6533  
2301−5913 23 01 36.19 −59 13 21.2 17.72 – – – – 117 – – – – 61 <2.3 – – PMNJ2301−5913 XM z= 0.149 
2303−6807 23 03 43.54 −68 07 37.6 16.26 924 205 1067 75 939 47 1013 22 1035 22 759 29 3.2 0.1 10.3 PKS2300−683 QX z= 0.512 
2306−6521 23 06 59.43 −65 21 32.1 >22 104: 23 – – 96 – – – – 372 11 <2.5 – – PKS2303−656 P z= 0.470 
2310−5941 23 10 28.48 −59 41 11.8 18.35 109: 24 [204] 16 134 180 162 74 <2.2 – – IRAS23074−5957 MI z= 0.1415 
2312−6607 23 12 58.80 −66 07 31.6 18.77 111: 25 287: 20 156 132 142 107 1.6 0.5 – PMNJ2312−6607  
2327−6644 23 27 45.38 −66 44 42.2 >22 184 25 187 13 176 240 272 470 14 4.7 0.4 <6.0 PKS2324−670 
2335−6637 23 35 12.26 −66 37 10.4 >22 118 26 – – 119 – – – – 3422 127 9.9 0.8 – PKS2332−66  
2348−6049 23 48 26.00 −60 49 20.1 21.17 – – 182 13 137 178 180 217 3.5 0.7 13.1 PKS2345−611  
2356−6820 23 56 00.75 −68 20 04.6 17.61 671: 97 795 56 781 39 588 11 702 13 1126 34 <0.4 – <6.0 PKS2353−68 CQP*z= 1.716 
2358−6052# 23 58 45.15 −60 52 49.7 16.61 680 108 240 17 248 12 344 820 15 29000 2900 5.2 – – PKS2356−61(N) MWV z= 0.0963 
2359−6057# 23 59 22.77 −60 57 17.5 16.61 275 61 – – – – – – – – – – – – – PKS2356−61(S)  
(1) Name (2) Radio position (J2000) (3) B (mag) (4) T (5) S18 2002 (6) ± (7) S18 2003 (8) ± (9) S20 2004 (10) ± (11) S8 2003 (12) ± (13) S5 2003 (14) ± (15) S843 SUMSS (16) ± (17) Polarization (per cent) (18) ± (19) Variability (per cent) (20) Alternate name (21) Notes 
0007−6113 00 07 20.85 −61 13 06.8 19.92 – – 145 10 150 142 143 87 <2.3 – <6.0 PMNJ0007−6112  
0024−6820 00 24 06.98 −68 20 54.4 17.62 366 14 338 24 256 13 388 471 1250 38 1.7 0.3 12.8 PKS0021−686 MX 
0025−6028# 00 25 15.91 −60 28 27.6 >22 94 19 – – 92 – – – – 1777 69 <7.6 – – PKS0022−60  
0103−6439 01 03 33.93 −64 39 08.0 18.88 290 58 200 14 333 19 215 173 770 69 <1.0 – 22.5 PKS0101−649 
0109−6049 01 09 15.61 −60 49 48.9 22.01 [872] 194 506 35 396 20 699 13 787 14 481 15 0.6 0.2 11.1 PKS0107−610 CQ 
0110−6315 01 10 16.87 −63 15 56.3 20.12 154: 34 278 19 208 10 165 155 178 <1.4 – 13.5 PKS0108−635 QP 
0112−6634 01 12 19.05 −66 34 45.3 17.86 415 92 295 21 348 17 413 474 16 451 49 3.0 0.2 6.5 PKS0110−668 QP 
0113−6753 01 13 11.50 −67 53 03.2 20.86 [127] 28 189 13 241 12 112 108 68 2.7 0.4 11.0 PMNJ0113−6753  
0121−6309# 01 21 40.64 −63 09 02.9 17.63 – – [121] 71 293 418 2650 97 <7.9 – – PKS0119−63 QX z= 0.837 
0144−6421 01 44 16.89 −64 21 42.9 21.35 286 20 172 12 175 201 188 108 4.8 0.6 <6.0 PMNJ0144−6421  
0154−6604 01 54 31.57 −66 04 16.4 18.87 – – 245 17 161 296 390 954 29 4.3 0.5 20.0 PKS0153−663 QP 
0158−6411 01 58 37.00 −64 11 28.4 19.51 133: 30 114 150 132 132 191 4.4 0.6 12.6 PMNJ0158−6411  
0158−6334 01 58 55.11 −63 34 49.7 19.29 [111] 25 119: 90 144 192 559 17 7.0 0.8 – PKS0157−638  
0201−6638 02 01 07.76 −66 38 12.9 20.26 – – 207 14 337 17 246 270 168 2.7 0.2 23.3 PMNJ0201−6638  
0206−6143 02 06 40.01 −61 43 32.4 20.01 – – 236: 17 209 11 205 211 220 3.7 0.2 – PMNJ0206−6143  
0207−6837 02 07 50.94 −68 37 55.0 20.15 – – 244 17 – – 300 332 400 12 – – – PKS0206−688 QP 
0208−6216 02 08 01.18 −62 16 35.6 18.24 158 35 – – 151 – – – – 193 <1.5 – – PMNJ0207−6216  
0214−7027 02 14 04.60 −70 27 06.3 19.35 [149] 33 – – 385 19 – – – – 108 1.0 0.2 – PMNJ0214−7027  
0214−6149 02 14 16.25 −61 49 33.8 20.33 248 55 316: 22 423 21 220 217 212 2.0 0.1 – PKS0212−620  
0219−6806 02 19 41.77 −68 06 18.2 20.08 – – 226: 16 170 221 279 729 22 1.3 0.4 – PKS0218−683 
0220−6330 02 20 54.20 −63 30 19.6 19.11 – – 367 26 367 18 333 363 368 11 2.0 0.2 <6.0 PKS0219−637 QP 
0230−6214 02 30 11.60 −62 14 35.5 19.20 – – 146 10 159 85 93 100 <1.0 – <6.0 PMNJ0230−6214  
0236−6136 02 36 53.25 −61 36 15.1 18.18 [511] 113 394 28 522 26 338 338 604 18 4.4 0.1 13.0 PKS0235−618 CQXP 
0247−6325 02 47 11.06 −63 25 38.3 17.87 – – 154 11 110 80 44 12 <1.8 – 15.9  
0250−6355 02 50 36.23 −63 55 01.6 19.67 – – 147 10 190 10 162 158 109 4.2 0.3 11.7 PMNJ0250−6355  
0251−6000 02 51 26.27 −60 00 06.3 19.78 – – 286 20 308 15 395 402 274 8.6 0.2 <6.0 PKS0250−602 QP 
0257−6112# 02 57 36.36 −61 12 30.4 18.78 – – 79 101 128 150 382 12 <2.3 – – PKS0256−614  
0303−6458 03 03 50.57 −64 58 54.5 >22 149 33 171 12 131 156 146 48 <1.5 – 12.2 PMNJ0303−6458 
0303−6211 03 03 50.67 −62 11 25.2 19.48 [2202] 489 1330 93 1256 63 1941 37 2181 40 2513 75 2.5 0.1 <6.0 PKS0302−623 CQXWV* 
0304−7007 03 04 18.26 −70 07 41.4 19.09 – – 190 13 160 271 311 238 3.7 0.4 6.9 PKS0304−703  
0309−6058 03 09 56.13 −60 58 38.9 19.00 – – 1207 84 1152 58 1244 24 1348 24 993 30 0.8 0.1 <6.0 PKS0308−611 CQWVP* 
0314−6548 03 14 22.44 −65 48 24.7 19.06 297 66 277 19 274 14 164 161 354 11 3.0 0.2 <6.0 PKS0313−660 QX z= 0.636 
0323−6026 03 23 08.44 −60 26 31.3 20.69 159: 35 263 18 222 11 220 223 199 2.2 0.2 6.8 PMNJ0323−6026  
0340−6811 03 40 06.53 −68 11 26.1 22.01 – – 200: 14 128 207 10 160 225 3.7 0.5 – PKS0339−683  
0340−6703 03 40 28.27 −67 03 16.6 19.24 [177] 39 256: 18 249 12 222 210 374 11 <0.8 – – PMNJ0340−6703  
0341−5954 03 41 21.60 −59 54 08.6 18.21 147 33 177 12 125 195 212 379 11 <2.0 – 16.4 PKS0340−600 
0355−6645 03 55 47.86 −66 45 33.9 19.00 – – 293 21 334 17 483 581 11 1403 42 1.6 0.2 <6.0 PKS0355−66 CQP 
0357−6948 03 57 30.07 −69 48 45.6 >22 [231] 51 – – 111 – – – – 148 <1.9 – – PMNJ0357−6948  
0408−6545 04 08 20.33 −65 45 08.7 >22 543 121 428 30 419 21 1540 30 3188 58 25029 751 3.6 0.2 <6.0 PKS0408−65 C* 
0420−6223 04 20 56.09 −62 23 38.6 >22 – – 188 13 179 482 896 16 5622 169 2.1 0.3 <6.0 PKS0420−62 
0421−6729 04 21 19.71 −67 29 01.6 20.16 – – 127 134 10 124 79 39 <1.4 – <6.0  
0422−6507 04 22 29.15 −65 07 05.0 20.42 [108] 24 – – 103 – – – – 177 2.1 0.6 – PMNJ0422−6507  
0425−6646 04 25 06.77 −66 46 49.8 20.59 [242] 54 236 17 218 11 315 361 91 2.4 0.3 <6.0 PKS0425−669  
0428−6438 04 28 10.87 −64 38 22.6 21.63 180 40 189 13 335 17 168 140 78 <0.7 – 27.4 PMNJ0428−6438  
0433−6030 04 33 34.08 −60 30 13.1 19.10 359: 80 356 25 315 16 324 325 414 13 2.0 0.2 <6.0 PKS0432−606 QP 
0436−6056 04 36 21.77 −60 56 37.3 21.85 – – [491] 44 116 – – – – 136 3.7 0.6 –  
0436−5931 04 36 51.52 −59 31 36.6 15.53 – – 149: 10 77 114 125 96 <2.3 – – ESO118−IG32 
0449−6106 04 49 24.33 −61 06 26.4 >22 – – 172 12 192 10 237 256 427 13 3.9 0.3 <6.0 PKS0448−611  
0504−6049 05 04 01.65 −60 49 52.5 19.43 [116] 26 [272] 19 168 – – – – 568 17 <1.2 – – PKS0503−608 QP 
0505−6215 05 05 46.75 −62 15 44.8 19.42 157 35 [287] 20 86 – – – – 54 <2.1 – – PMNJ0505−6215  
0505−6236 05 05 48.53 −62 36 11.0 20.80 152 34 [201] 16 87 – – – – 110 2.9 0.7 – PMNJ0505−6236  
0506−6109 05 06 43.96 −61 09 41.0 17.16 – – 1883 131 1819 91 1756 34 1791 33 3102 93 1.2 0.1 <6.0 PKS0506−61 QXWE*z= 1.093 
0507−6104 05 07 54.62 −61 04 43.2 21.18 – – 232 16 443 22 336 420 842 25 0.6 0.2 30.8 MRC0507−611  
0516−6207 05 16 44.89 −62 07 05.4 21.20 [530] 118 545: 38 785 39 414 416 418 13 2.8 0.1 –. PKS0516−621 QP 
0522−6107 05 22 34.39 −61 07 57.2 18.46 [1101] 244 462 32 425 21 654 13 700 13 741 22 0.8 0.2 <6.0 PKS0522−611 CQXP z= 1.400 
0534−6106 05 34 35.73 −61 06 07.0 19.29 513 47 503 35 426 30 435 491 451 14 1.6 0.2 6.6 PKS0534−611 QP 
0546−6415 05 46 41.83 −64 15 22.1 16.54 – – 227 16 363 21 189 243 119 <0.6 – 22.5 PMNJ0546−6415 QXW z= 0.323 
0607−6031 06 07 55.13 −60 31 52.0 19.50 – – 161 11 256 13 286 406 1416 43 1.7 0.2 26.1 PKS0607−605 
0610−6058 06 10 30.36 −60 58 37.8 20.15 – – 145: 10 130 186 215 350 11 2.9 0.4 – PKS0609−609 QX 
0620−6107 06 20 05.24 −61 07 31.6 19.99 – – 167 12 235 12 255 287 357 11 10.0 0.3 16.1  
0621−5935 06 21 53.13 −59 35 08.6 19.68 – – 222 16 237 12 396 547 10 1276 38 0.8 0.2 <6.0 PKS0621−595  
0623−6436 06 23 07.75 −64 36 20.7 17.06 – – 481 34 1222 61 368 312 326 13 0.5 0.1 43.2 PMNJ0623−6436 XMI z= 0.1289 
0625−6020 06 25 24.32 −60 20 29.8 >22 – – 269 19 351 18 342 365 288 <0.6 – 12.2 PMNJ0625−6020  
0628−6248 06 28 57.54 −62 48 45.0 21.24 – – 327 23 359 18 396 426 522 16 7.1 0.2 <6.0 PKS0628−627 
0644−6712 06 44 28.15 −67 12 57.6 21.53 – – 230 16 368 18 225 233 218 6.6 0.2 22.5 PKS0644−671 
0647−6058 06 47 40.86 −60 58 05.3 >22 – – 145: 10 97 93 98 108 2.4 0.5 – PMNJ0647−6058  
0650−6510 06 50 57.62 −65 10 12.3 18.69 – – 91 97 174 207 71 3.6 0.6 <6.0 PMNJ0650−6509  
0700−6610 07 00 31.16 −66 10 45.2 15.77 – – 235 16 306 15 293 298 288 3.0 0.2 12.1 PKS0700−661 QP 
0715−6829 07 15 09.51 −68 29 58.2 – – – – 209 15 327 16 236 239 143 6.0 0.2 21.4 PMNJ0715−6829  
0716−6240 07 16 33.57 −62 40 26.5 20.27 – – 316 22 364 18 226 182 116 2.7 0.2 <6.0 PKS0716−625  
0719−6218 07 19 04.55 −62 18 02.5 20.73 – – 249 17 – – 249 13 282 284 – – – PMNJ0719−6218  
0738−6735 07 38 56.49 −67 35 50.6 19.65 – – 255 18 346 17 396 434 531 16 2.2 0.2 14.3 PKS0738−674 QP z= 1.663 
0743−6726# 07 43 31.60 −67 26 25.8 16.71 – – 1069 214 1360 68 1904 38 2109 42 5638 169 4.8 0.1 – PKS0743−67 QXWVP z= 1.510 
0744−6919 07 44 20.26 −69 19 07.3 21.65 237 53 323 23 363 18 330 322 414 12 2.4 0.2 <6.0 PKS0744−691  
0746−6612 07 46 43.66 −66 12 51.4 19.32 – – [371] 27 168 – – – – 2089 63 12.0 0.4 – PKS0746−660  
0806−6101 08 06 49.26 −61 01 29.8 >22 – – 108 147 175 182 163 3.1 0.6 14.4 PMNJ0806−6101  
0818−6634 08 18 49.39 −66 34 00.4 19.12 – – 111 114 127 96 28 <2.7 – <6.0 PMNJ0818−6634  
0820−6814 08 20 11.23 −68 14 40.8 21.52 – – 193 14 64 156 121 53 <4.2 – 49.9 PMNJ0820−6814  
0835−5953 08 35 28.91 −59 53 11.6 >22 – – 269 19 307 15 194 140 25 0.9 0.2 <6.0 PMNJ0835−5953  
0842−6053 08 42 26.48 −60 53 50.4 19.98 – – 318 22 320 16 376 398 745 22 1.2 0.2 <6.0 PMNJ0842−6053 
0845−6527 08 45 11.29 −65 27 23.8 18.01 [237] 53 260 18 214 11 403 422 18 1.1 0.3 8.3 PMNJ0845−6527  
0846−6313 08 46 35.97 −63 13 34.8 19.34 108 24 – – 73 – – – – 86 4.4 1.0 – PMNJ0846−6313  
0847−6235 08 47 02.95 −62 35 40.8 19.16 – – 117 108 140 149 191 2.7 0.8 <6.0 PMNJ0847−6235  
0901−6636 09 01 15.40 −66 36 33.8 21.38 [230] 51 160 11 165 249 266 193 4.5 0.6 <6.0 PKS0900−664  
0923−6648 09 23 47.51 −66 48 37.9 21.78 – – 150: 11 179 137 123 96 6.4 0.5 – PKS0922−666  
0938−6556 09 38 41.82 −65 56 13.6 18.39 – – 104 – – 140 119 197 <1.7 – – PKS0937−657  
0953−6924 09 53 20.48 −69 24 25.4 18.65 – – 198: 14 103 184 195 170 3.5 0.7 – PKS0952−691 QP 
1533−6837 15 33 34.61 −68 37 19.3 21.63 – – 223 12 285 14 – – – – 285 10 <1.3 – 11.1 PKS1528−684  
1542−6807 15 42 57.32 −68 07 49.8 16.77 – – 125: 16 58 – – – – 243 <5.9 – – PMNJ1543−6808  
1546−6837 15 46 44.52 −68 37 29.3 19.51 [233] 52 131 503 25 – – – – 206 2.8 0.2 58.4 PMNJ1546−6837  
1624−6809 16 24 18.55 −68 09 11.3 17.05 331: 16 570 40 723 36 910 17 1473 27 1046 31 0.6 0.2 10.7 PKS1619−680 CQP*z= 1.360 
1647−6438 16 47 37.91 −64 38 00.2 20.05 614: 136 418 29 462 23 424 557 10 644 19 8.6 0.2 <6.0 MRC1642−645 CVE 
1703−6212 17 03 36.78 −62 12 39.1 18.73 – – 1572 110 1287 64 854 17 1223 22 731 22 0.5 0.1 8.6 MRC1659−621 CWE 
1703−6511 17 03 50.56 −65 11 06.2 18.10 [99] 22 – – 135 – – – – 345 10 2.2 0.6 – PKS1658−651  
1709−6905 17 09 55.80 −69 05 22.6 20.34 – – 122 148 70 86 56 <2.1 – 8.2 PMNJ1709−6905  
1721−6154 17 21 39.07 −61 54 42.8 18.91 [340] 75 381 27 297 15 288 285 310 2.5 0.3 11.3 PMNJ1721−6154  
1723−6500 17 23 41.12 −65 00 36.3 13.16 [2945] 654 2671 187 2817 141 2626 51 – – 3724 112 <1.7 – <6.0 NGC6328 CMWVP*z= 0.0142 
1726−6427 17 26 57.91 −64 27 52.4 >22 204 13 209 15 150 344 1041 19 4076 122 <1.8 – 15.6 MRC1722−644 CV 
1735−6215 17 35 08.11 −62 15 21.2 19.59 [256] 57 403 28 300 15 262 403 696 21 1.1 0.3 13.7 MRC1730−622  
1736−5951 17 36 30.95 −59 51 58.3 21.51 236 62 181 13 192 10 151 242 269 2.5 0.4 <6.0 PKS1732−598 
1737−5921 17 37 19.80 −59 21 41.0 20.99 – – 395: 28 247 12 253 368 381 12 5.5 0.3 – PMNJ1737−5921  
1743−6626 17 43 49.13 −66 26 27.5 20.76 176 39 124 192 10 74 117 209 2.7 0.5 20.9 PKS1738−664  
1749−6258 17 49 25.80 −62 58 17.8 19.08 182 40 181 13 186 111 162 244 2.4 0.4 <6.0 PMNJ1749−6258  
1754−6423 17 54 42.21 −64 23 45.3 19.15 83: 18 – – 103 – – – – 177 <2.6 – – PMNJ1754−6423  
1759−5947 17 59 06.08 −59 47 01.1 >22 112 25 – – 67 – – – – 5626 169 13.0 0.9 – PKS1754−59  
1803−6507 18 03 23.58 −65 07 36.8 18.19 [999] 222 1144 80 1314 66 771 19 – – 637 19 0.8 0.1 <6.0 PKS1758−651 CWP 
1807−6413 18 07 54.03 −64 13 50.7 20.56 450 100 – – 277 14 – – – – 94 1.8 0.2 – PMNJ1807−6413  
1807−7012# 18 07 14.76 −70 12 39.9 18.23 131 13 – – 126 – – – – 1199 36 13.2 1.7 – PKS1801−702 
1819−6345 18 19 34.94 −63 45 48.5 16.80 1631 79 – – 1825 91 – – – – 20185 606 0.8 0.1 – PKS1814−63 CMWE*z= 0.0627 
1822−6359# 18 22 14.76 −63 59 24.4 >22 142 28 – – 163 – – – – 4935 181 6.1 0.7 – PKS1817−64  
1824−6717# 18 24 34.21 −67 17 26.1 >22 228 46 – – 310 20 – – – – 3440 134 4.1 0.4 – PKS1819−67  
1836−6649 18 36 59.40 −66 49 08.5 19.54 127 28 – – 146 – – – – 3260 98 4.7 0.4 – PKS1831−668  
1840−6152 18 40 15.43 −61 52 06.3 21.96 245 54 282 20 254 13 – – – – 191 1.1 0.2 <6.0 PKS1835−619  
1844−6808 18 44 11.82 −68 08 05.3 20.00 – – 188 13 114 – – – – 111 2.9 0.6 23.9 PMNJ1844−6808  
1852−6848 18 52 32.29 −68 48 16.1 >22 101: 22 – – 86 – – – – 403 12 4.0 0.6 – PKS1847−688  
1903−6749 19 03 01.32 −67 49 35.5 18.90 419: 21 156 11 481 24 – – – – 232 5.2 0.1 50.7 PMNJ1903−6749  
1906−6556 19 06 47.72 −65 56 41.1 >22 – – [264] 18 111 – – – – 447 14 2.1 0.4 – PKS1901−660  
1913−6950 19 13 31.25 −69 50 37.4 >22 282 63 317 22 192 10 – – – – 34 <0.9 – 24.0  
1916−6928 19 16 36.33 −69 28 33.7 >22 – – 225: 16 117 – – – – 100 3.6 0.4 – PMNJ1916−6928  
1917−6436 19 17 34.06 −64 35 43.8 20.55 – – 116: 64 – – – – 102 6.5 0.7 – PMNJ1917−6435  
1923−6320 19 23 24.64 −63 20 46.2 21.42 – – 184 13 127 – – – – 412 13 1.8 0.4 17.6 PMNJ1923−6320  
1926−6242 19 26 58.09 −62 42 27.6 18.64 133: 30 – – 93 – – – – 139 3.5 0.5 –  
1930−6056 19 30 06.07 −60 56 09.0 20.57 675 150 819 57 572 29 – – – – 696 21 3.1 0.1 17.0 PKS1925−610 CQP 
1933−6942 19 33 31.22 −69 42 58.5 19.94 388 86 – – 259 13 – – – – 744 22 1.2 0.2 – PKS1928−698 QP 
1939−6342 19 39 24.99 −63 42 45.3 18.87 [1272] 350 1227 86 886 44 – – – – 13722 412 <0.2 – <6.0 PKS1934−63 CV*z= 0.183 
1940−6907 19 40 26.09 −69 07 55.1 >22 [568] 126 556 39 442 22 – – – – 1705 51 2.1 0.1 10.3 PKS1935−692 CQV z= 3.154 
1940−6527 19 40 38.91 −65 27 15.7 20.75 – – 242 13 282 14 – – – – 244 0.7 0.2 <6.0 PMNJ1940−6527  
1941−6211 19 41 21.74 −62 11 21.3 21.12 502: 111 390 27 348 17 – – – – 1832 55 4.0 0.2 <6.0 PKS1936−623 QP* 
1942−7015 19 42 45.52 −70 15 44.4 19.29 111 25 – – 75 – – – – 80 2.6 0.7 – PMNJ1942−7015  
2004−6347 20 04 29.52 −63 47 22.7 19.35 456 13 355 25 369 18 369 560 10 749 23 1.5 0.2 <6.0 PMNJ2004−6347 
2015−6712 20 15 00.00 −67 12 58.9 19.02 [73] 16 – – 214 11 – – – – 39 <1.0 – – PMNJ2014−6713 
2017−6824 20 17 29.30 −68 24 54.9 21.99 – – 175 12 164 175 227 243 4.3 0.4 <6.0 PKS2012−685 QP 
2021−6124 20 21 01.34 −61 24 49.2 20.45 183 41 163 11 200 10 321 468 1071 32 4.2 0.3 14.0 PKS2016−615 CQ 
2024−6458 20 24 46.30 −64 58 35.6 20.79 – – [267] 21 192 10 – – – – 126 2.7 0.3 – PMNJ2024−6458  
2027−7007 20 27 24.54 −70 07 17.2 19.19 [308] 68 – – 233 12 – – – – 1041 31 1.7 0.3 – PKS2022−702 Q z= 0.697 
2035−6846 20 35 48.85 −68 46 33.6 19.27 – – 570 40 457 23 651 13 745 14 299 4.2 0.2 9.8 PKS2030−689 QWP 
2035−6602 20 35 51.46 −66 02 07.3 19.24 – – 320 22 259 13 325 386 355 11 3.6 0.2 9.2 PMNJ2035−6602  
2046−6527 20 46 49.64 −65 27 27.4 21.58 116 26 – – 130 – – – – 36 <1.5 – – PMNJ2046−6527  
2048−6804 20 48 23.81 −68 04 51.8 18.20 – – 114 104 122 170 349 11 1.9 0.5 <6.0 PKS2043−682 
2052−6523 20 52 06.64 −65 23 11.3 17.29 – – 275 19 228 11 275 15 375 551 17 1.3 0.3 7.9 PKS2047−655 QP z= 2.320 
2053−6255 20 53 05.62 −62 55 50.9 21.19 – – 236 17 280 14 269 313 171 1.8 0.2 6.9 PMNJ2053−6255  
2059−6745 20 59 09.59 −67 45 23.2 17.70 90 20 – – 104 – – – – 2456 <2.0 – – PMNJ2059−6745 
2106−6547 21 06 59.73 −65 47 44.2 20.88 303 67 315 22 305 15 424 585 11 1555 47 <0.7 – <6.0 PKS2102−659 
2114−6851 21 14 13.46 −68 51 02.4 19.58 140: 31 189 13 223 11 225 285 510 15 2.6 0.3 6.5 PKS2109−690 Q z= 2.910 
2121−6111 21 21 04.10 −61 11 24.2 18.75 214: 48 287 20 357 18 367 476 966 29 2.1 0.2 9.6 MRC2117−614 
2121−6404 21 21 55.05 −64 04 29.8 21.19 – – 263: 18 164 354 588 11 2081 62 <1.1 – – PKS2117−64 
2124−6028 21 24 02.94 −60 28 08.9 17.32 – – [323] 23 134 – – – – 35 <1.5 – –  
2134−6513 21 34 13.25 −65 13 36.9 21.21 – – 166 12 179 136 142 213 6.2 0.4 <6.0 PKS2130−654  
2136−6335 21 36 22.09 −63 35 51.3 19.77 – – 238 17 385 19 180 144 160 0.7 0.2 23.0 PMNJ2136−6335  
2141−6411 21 41 46.50 −64 11 14.8 19.58 – – 200 14 217 11 153 152 176 5.8 0.3 <6.0 PMNJ2141−6411  
2150−6802 21 50 13.43 −68 02 50.6 20.83 215: 48 179 13 246 12 230 229 126 1.0 0.2 14.9 PMNJ2150−6803  
2156−6331 21 56 49.11 −63 31 05.9 19.98 97 22 – – 141 – – – – 57 <1.6 – – PMNJ2156−6331  
2157−6941# 21 57 05.45 −69 41 22.6 13.85 1821 304 [759] 53 1490 75 2760 59 8300 171 41200 1455 2.4 0.1 – ESO075−G41 IXWM z= 0.0283 
2203−6130 22 03 59.63 −61 30 21.9 19.86 249 55 282: 20 289 14 264 346 441 13 3.5 0.2 – PKS2200−617 QP 
2208−6325 22 08 47.15 −63 25 47.6 18.41 [298] 66 335 23 337 17 453 634 12 1429 43 4.2 0.2 <6.0 PKS2204−63 CQ z= 0.618 
2213−6330 22 13 34.73 −63 30 01.5 18.52 325 72 322 23 334 17 223 209 631 25 1.4 0.2 <6.0 PKS2210−637 
2215−6609 22 15 45.26 −66 09 14.0 21.19 110 24 – – 134 – – – – 761 23 4.4 0.5 – PKS2212−664  
2229−6910 22 29 00.21 −69 10 29.8 19.85 – – 596 42 626 31 549 11 491 400 12 0.8 0.1 <6.0 PKS2225−694 QP 
2230−6310 22 30 10.29 −63 10 43.1 19.85 187 42 144 10 156 184 193 231 3.4 0.4 <6.0 PMNJ2230−6310  
2231−6231 22 31 07.91 −62 31 19.2 20.25 [395] 88 316 22 249 12 346 332 267 1.5 0.2 10.7 PKS2227−627  
2243−6250 22 43 07.78 −62 50 57.3 18.19 – – 199 14 224 11 224 194 111 1.2 0.2 <6.0 PKS2239−631 
2254−5926 22 54 56.77 −59 26 00.7 19.80 – – 239: 17 194 10 159 157 159 1.8 0.3 – PKS2251−596 
2256−6533 22 56 24.89 −65 33 25.1 16.90 – – 114 99 125 150 349 10 3.0 0.6 <6.0 PMNJ2256−6533  
2301−5913 23 01 36.19 −59 13 21.2 17.72 – – – – 117 – – – – 61 <2.3 – – PMNJ2301−5913 XM z= 0.149 
2303−6807 23 03 43.54 −68 07 37.6 16.26 924 205 1067 75 939 47 1013 22 1035 22 759 29 3.2 0.1 10.3 PKS2300−683 QX z= 0.512 
2306−6521 23 06 59.43 −65 21 32.1 >22 104: 23 – – 96 – – – – 372 11 <2.5 – – PKS2303−656 P z= 0.470 
2310−5941 23 10 28.48 −59 41 11.8 18.35 109: 24 [204] 16 134 180 162 74 <2.2 – – IRAS23074−5957 MI z= 0.1415 
2312−6607 23 12 58.80 −66 07 31.6 18.77 111: 25 287: 20 156 132 142 107 1.6 0.5 – PMNJ2312−6607  
2327−6644 23 27 45.38 −66 44 42.2 >22 184 25 187 13 176 240 272 470 14 4.7 0.4 <6.0 PKS2324−670 
2335−6637 23 35 12.26 −66 37 10.4 >22 118 26 – – 119 – – – – 3422 127 9.9 0.8 – PKS2332−66  
2348−6049 23 48 26.00 −60 49 20.1 21.17 – – 182 13 137 178 180 217 3.5 0.7 13.1 PKS2345−611  
2356−6820 23 56 00.75 −68 20 04.6 17.61 671: 97 795 56 781 39 588 11 702 13 1126 34 <0.4 – <6.0 PKS2353−68 CQP*z= 1.716 
2358−6052# 23 58 45.15 −60 52 49.7 16.61 680 108 240 17 248 12 344 820 15 29000 2900 5.2 – – PKS2356−61(N) MWV z= 0.0963 
2359−6057# 23 59 22.77 −60 57 17.5 16.61 275 61 – – – – – – – – – – – – – PKS2356−61(S)  

The columns in Table 3 are as follows.

  1. The AT source name, followed by # if the source is resolved or double at 20 GHz (see Section 3.4).

  2. The radio position (J2000.0) measured from the 20 GHz images. For resolved doubles, the listed position is the radio centroid.

  3. For sources where we were able to make an optical identification on the Digitized Sky Survey (DSS), this column lists the bJ magnitude from the SuperCOSMOS data base.

  4. The object type of the optical ID, as classified in SuperCOSMOS: T= 1 for a galaxy, T= 2 for a stellar object (QSO candidate). T= 0 indicates either a blank field at the source position or a faint (>22 mag) object for which the SuperCOSMOS star/galaxy separation is unreliable.

  5. The 18 GHz flux density measured in 2002, followed by its error. For resolved doubles, we list the integrated flux density over the source. Flux densities in square brackets [] are measurements made at offsets of more than 80 arcsec from the imaging field centre at 18–20 GHz, and should be regarded as unreliable because of the large primary-beam correction. Flux densities followed by a colon are measured at offsets of 60–80 arcsec from the field centre, but should be reliable.

  6. The 18 GHz flux density measured in 2003, and its error.

  7. The 20 GHz flux density measured in 2004, and its error.

  8. The 8.6 GHz flux density measured in 2003, and its error.

  9. The 4.8 GHz flux density measured in 2003, and its error.

  10. The integrated flux density at 843 MHz and its error, from the Sydney University Molonglo Sky Survey (SUMSS) catalogue (Mauch et al. 2003).

  11. The fractional linear polarization at 20 GHz measured in 2004, and its error.

  12. The debiased variability index at 20 GHz, calculated as described in Section 5.1.

  13. Alternative source name, from the NASA/IPAC Extragalactic Database (NED).

  14. Notes on individual sources, coded as follows:

  15. C = listed in the online ATCA calibrator catalogue,

  16. E = possible EGRET gamma-ray source (Tornikoski et al. 2002),

  17. I = listed as an IRAS galaxy in the online NED,

  18. M = galaxy detected in the near-infrared two-Micron All-Sky Survey,

  19. P = in the Parkes quarter-Jy sample (Jackson et al. 2002),

  20. Q = listed as a QSO in NED,

  21. V = VLBI observation with the VSOP satellite (Hirabayashi et al. 2000),

  22. W = source detected in the first-year Wilkinson Microwave Anisotropy Probe (WMAP) data (Bennett et al. 2003),

  23. X = listed as an X-ray source in NED,

  24. *= polarization observation by Ricci et al. (2004b).

3.4 Extended sources at 20 GHz

The great majority of the sources detected in the 20 GHz pilot survey are unresolved in our follow-up images at 5, 8 and 20 GHz. The source-detection algorithm used in the pilot survey was optimized for point sources, and there will be some bias against extended sources with angular sizes larger than about 30 arcsec. For sources larger than 1 arcmin in size, the total flux densities listed in Table 3 may also be underestimated.

Only 11 of the 173 sources in Table 3 were resolved in our (15-arcsec resolution) 20 GHz images. The overall properties of extended sources in the current sample are as follows.

  • Four objects, J0103−6439, J2157−6941 and J2358−6052/J2359−6057, are very extended double-lobed radio sources which are too large to be imaged with these ATCA snapshots. As a result, the total flux densities listed in Table 3 are lower limits to the correct value.

  • Another seven sources are resolved in our ATCA images, but still lie within the 2.2 arcmin primary beam of the ATCA at 20 GHz. Details of these objects are given in Appendix A.

  • Five of the extended sources (J0103−6439, J0121−6309, J0257−6112, J0743−6726 and J2157−6941) have a flat-spectrum core which dominates the flux density at 20 GHz.

Since the number of extended sources is small, and they appear to be somewhat diverse in nature, we defer any detailed discussion of the extended radio-source population to a later paper.

3.5 Optical identification of the 20 GHz sources

We examined all the sources in Table 3 in the SuperCOSMOS online catalogue and images (Hambly et al. 2001). An optical object was accepted as the correct ID for a 20 GHz radio source if it was brighter than bJ= 22 mag and lay within 2.5 arcsec of the radio position. For one source in Table 3 (J0715−6829) the optical image was saturated by light from a nearby 11th magnitude star and so no identification could be attempted. Of the remaining 172 sources, 146 (85 per cent) had an optical ID which met the criteria listed above. Monte Carlo tests (based on matching the SuperCOSMOS catalogue with radio positions randomly offset from those in Table 3) imply that at least 97 per cent of these IDs are likely to be genuine associations, rather than a chance alignment with a foreground or background object.

As can be seen from Fig. 4, the majority (65 per cent) of radio sources selected at 20 GHz have stellar IDs on the DSS B images, and are candidate QSOs or BL Lac objects. 20 per cent of the radio sample are identified with galaxies and 15 per cent are faint objects or blank fields. The overall optical identification rate of 85 per cent for radio sources selected at 20 GHz is significantly higher than the identification rate for bright radio sources selected at 1.4 GHz (typically ∼30 per cent above B∼22 mag), but is closer to that found by Bolton et al. (2004) for a flux-limited sample of radio sources selected at 15 GHz, as discussed in Section 8.1.1.

Fig. 5 shows the relation between bJ magnitude and redshift for the 22 sources (13 per cent of the objects in Fig. 4) which currently have a published redshift. A representative sample of nearby radio galaxies (Sadler et al. 2002) selected from the 2dF Galaxy Redshift Survey (2dFGRS; Colless et al. 2001) is shown for comparison. Galaxies detected in our 20-GHz survey appear to span a narrow range in optical luminosity similar to that seen in nearby radio galaxies selected at lower frequencies, though we caution that the sub-sample of sources with published redshifts is inhomogeneous in nature and may be biased in luminosity and/or redshift distribution because redshifts are easier to measure for brighter galaxies and QSOs.

Figure 5

Relation between SuperCOSMOS bJ magnitude and redshift for those objects in our sample which have a published redshift. Open circles show galaxies from the 20 GHz sample and filled circles QSOs. The small crosses show a representative subsample of 2dFGRS radio galaxies selected at 1.4 GHz (Sadler et al. 2002). The highest redshift so far measured for an object in this sample is for J1940−6907, a QSO at z= 3.154.

Figure 5

Relation between SuperCOSMOS bJ magnitude and redshift for those objects in our sample which have a published redshift. Open circles show galaxies from the 20 GHz sample and filled circles QSOs. The small crosses show a representative subsample of 2dFGRS radio galaxies selected at 1.4 GHz (Sadler et al. 2002). The highest redshift so far measured for an object in this sample is for J1940−6907, a QSO at z= 3.154.

4 RELIABILITY AND REPRODUCIBILITY OF THE SCANNING SURVEY

As noted earlier, the fact that our pilot survey scanned the same area of sky in both 2002 and 2003 provides an important test of the observational techniques to be used for the full AT20G survey (i.e. fast scans of large areas of sky, followed by imaging of candidate sources identified in the scans). In particular, how good a job does the scanning technique do in finding genuine sources down to the nominal detection limit, and how reproducible are the source lists produced by this technique?

Table 4 shows the recovery rate in 2003 of sources detected in the 2002 pilot survey scans. As might be expected (since the nominal detection limit of the 2003 survey was 100 mJy), none of the weakest (S18 < 100 mJy) sources detected in 2002 was recovered in the 2003 scans, but the recovery rate rises to 95 per cent for sources with measured flux densities above 150 mJy in 2002. We checked the three sources above 150 mJy which were not recovered in 2003. In all cases these sources were visible in the raw data scans, so had not decreased in flux density to below the survey limit. Instead, they were missed from the follow-up imaging program because of deficiencies in the source-detection algorithm for extended sources or sources with nearby bad data points. For the full AT20G survey, we will use an improved source-detection algorithm.

Table 4

The fraction of sources detected at 18 GHz in the 2002 scans which were independently detected in the 2003 scans of the pilot survey area.

S18 (mJy) Observed in 2002 Recovered in 2003 Fraction recovered (per cent) 
<100 
101–125 13 31 
126–150 63 
151–200 12 12 100 
>200 50 47 94 
S18 (mJy) Observed in 2002 Recovered in 2003 Fraction recovered (per cent) 
<100 
101–125 13 31 
126–150 63 
151–200 12 12 100 
>200 50 47 94 

Fig. 1 compares the 18 GHz flux densities measured in 2002 and 2003 for sources detected in both years. It implies that the flux-density scales are in good agreement, and gives some first hints that the general variability level at 18 GHz is modest (though the large error bars on the 2002 flux densities mean that this is not a very useful data set for studying variability in a quantitative way). We therefore conclude that the scanning technique produces a reliable and robust catalogue of sources, in the sense that rescanning an area of sky will produce essentially the same source catalogue each time.

5 RADIO SPECTRA OF THE 20 GHZ SOURCES

5.1 Representative radio spectra at 0.8–20 GHz

Fig. 6 shows some representative radio spectra for sources in our sample. It is clear we see a wide variety of spectral shapes, most of which cannot be fitted by a single power law over the frequency range 1–20 GHz. We can distinguish four main kinds of spectra.

Figure 6

Examples of radio spectra for each of the four spectral classes identified in the text (Upturn, Rising, Steep and Peak), together with a spectrum classified as Flat (|α| < 0.1 for both 0.84–5 GHz and 8–20 GHz). Where available, a 408 MHz flux density from the MRC (Large et al. 1981) is plotted in addition to the data from Table 3.

Figure 6

Examples of radio spectra for each of the four spectral classes identified in the text (Upturn, Rising, Steep and Peak), together with a spectrum classified as Flat (|α| < 0.1 for both 0.84–5 GHz and 8–20 GHz). Where available, a 408 MHz flux density from the MRC (Large et al. 1981) is plotted in addition to the data from Table 3.

  • Sources with steep (falling) spectra over the whole range 843 MHz to 20 GHz (e.g. J0408−6545 in Fig. 6).

  • Sources with peaked (GPS) spectra, in which the flux density rises at low frequency and falls at high frequency (e.g. J0201−6638).

  • Sources with inverted (rising) radio spectra over the whole frequency range (e.g. J0113−6753).

  • Sources with an upturn in their spectrum, where the flux density is falling at lower frequencies, but then turns up and begins to rise above 5–8 GHz (e.g. J2213−6330).

In addition, a small number of sources have flat radio spectra in which the flux density is essentially constant over the entire frequency range observed (e.g. J0220−6330 in Fig. 6).

The radio spectral index

 
formula

where S1 and S2 are the measured flux densities at frequencies ν1 and ν2, is commonly used to characterize radio-source populations at centimetre wavelengths (frequencies of 1–5 GHz) where many large-area radio surveys have been carried out.

At centimetre wavelengths the radio emission from flat-spectrum (α > −0.5) objects is dominated by a compact, self-absorbed component, while steep-spectrum objects (α < −0.5) are dominated by optically thin synchrotron emission. The flat- and steep-spectrum populations are usually considered separately when modelling the cosmic evolution of radio sources (e.g. Peacock & Gull 1981; Peacock 1985).

As pointed out by Peacock (1985), the radio spectral index is only valid as a diagnostic tool if it is measured over a frequency interval small enough that the effects of spectral curvature can be neglected. Because many of the sources in our sample have significant spectra curvature over the frequency range 1–20 GHz, we therefore use a ‘radio two-colour’ diagram, rather than a single spectral index, to characterize the high-frequency radio-source population. As discussed in the next section, this diagram compares a low-frequency spectral index αL (which corresponds closely to the spectral index traditionally used to separate flat- and steep-spectrum radio sources) with a high-frequency spectral index αH which measures the spectral shape above 8 GHz.

5.2 The radio two-colour diagram

Fig. 7 shows the radio two-colour diagram, which compares the spectral indices αL (at 0.84–5 GHz) and αH (at 8–18 GHz) for sources selected at 20 GHz. Such a diagram is analogous to the two-colour diagram used in optical astronomy to characterize the broad-band continuum properties of stars and galaxies. The diagram shown in Fig. 7 has the advantage that the axes (and error bars) are independent, and the four main spectral classes identified in Fig. 6 correspond to the four quadrants in the two-colour diagram. The dotted line shows the relation for galaxies whose spectra follow a single power law from 0.8 to 18 GHz. Only a small fraction of sources fall on or near the dotted line, and it is clear that αL and αH are not strongly correlated.

Figure 7

Radio ‘two-colour diagram’ for the 119 extragalactic sources in Table 3 which have good-quality multifrequency observations made in late 2003.

Figure 7

Radio ‘two-colour diagram’ for the 119 extragalactic sources in Table 3 which have good-quality multifrequency observations made in late 2003.

As can be seen from Table 5, over 30 per cent of the sources in Fig. 7 have flat or inverted spectra between 8 and 20 GHz (i.e. αH > 0), and more than half of these (like J2213−6330 in Fig. 6) have steep radio spectra below 5 GHz and would not have been predicted as strong 20 GHz sources on the basis of their low-frequency spectra. In contrast, many sources with flat or inverted spectra below 5 GHz turn over and become steep above 8 GHz.

Table 5

Distribution of our sample in the five spectral classes defined in Section 4.1 and Fig. 6.

Spectrum How defined Number Fraction (per cent) 
Steep αL < 0, αH < 0 32 32 ± 6 
Upturn αL < 0, αH > 0 22 22 ± 5 
Rising (inverted) αL > 0, αH > 0 18 18 ± 4 
Peak αL > 0, αH < 0 23 23 ± 4 
Flat −0.1 < (αL, αH) < 0.1 6 ± 2 
Total  101  
Spectrum How defined Number Fraction (per cent) 
Steep αL < 0, αH < 0 32 32 ± 6 
Upturn αL < 0, αH > 0 22 22 ± 5 
Rising (inverted) αL > 0, αH > 0 18 18 ± 4 
Peak αL > 0, αH < 0 23 23 ± 4 
Flat −0.1 < (αL, αH) < 0.1 6 ± 2 
Total  101  

6 VARIABILITY AT 20 GHZ

6.1 Previous work

As mentioned in the introduction, there have been only a few studies of radio-source variability at frequencies above 5 GHz. Owen, Spangler & Cotton (1980) investigated the variability of a sample of strong (S90 > 1 Jy) flat-spectrum sources at 5 and 90 GHz over a one-year period. They found that these sources were only slightly more variable at 90 GHz than at 5 GHz, in contrast to what they had expected. Tingay et al. (2003) also found that the level of variability of strong, compact radio sources increased only moderately with frequency. They used the ATCA to monitor a sample of 202 sources from the VSOP all-sky survey at 1.4, 2.5, 4.8 and 8.6 GHz, and found a median variability of 6 per cent at 1.4 GHz and 9 per cent at 8.6 GHz over a time-scale of 3–4 yr. Barvainis et al. (2005) found similar variability levels at 8.5 GHz for a sample of radio-loud and radio-quiet QSOs observed at the Very Large Array.

These studies are based largely on objects pre-selected at lower frequencies, and may not give a complete picture of the variability of the 20 GHz source population as a whole.

6.2 Quantifying variability

Following Barvainis et al. (2005) and Akritas & Bershady (1996), we use a debiased variability index which takes into account the uncertainties in individual flux-density measurements. We define the fractional variability index, Vrms by

 
formula

where Si are individual flux-density measurements for the same source, σi is the error on each measurement, N is the number of data points, and 〈S〉 is the mean flux density. We follow Barvainis et al. (2005) in setting the variability index to be negative when the value inside the square root becomes negative. However, rather than listing negative values of the variability index, as was done by Barvainis et al. (2005), we used the distribution of positive and negative values to define the minimum level of variability which is detectable in our data. This was found to be 6 per cent, so for all sources with a variability index below this we list the debiased variability index as <6.0 per cent.

We used only the 2003 and 2004 data sets in our variability analysis, since these have significantly smaller flux-density errors than the 2002 data. The 2003 imaging observations were made at 18 GHz and the 2004 observations at 20 GHz, so there is a possibility of measuring spurious ‘variability’ for sources which have steeply falling radio spectra at 18–20 GHz. To overcome this, we used the 8–18 GHz spectral index from Table 3 to extrapolate the 2003 measurements to 20 GHz for the small number of sources in Table 3 which have α < −0.7 between 8 and 18 GHz. As discussed in Section 2.3, different ATCA primary flux calibrators were also used for the 2003 and 2004 observing runs. Since there appears to be no systematic offset between our 2003 and 2004 flux density measurements at 20 GHz (see Fig. 2), we do not believe that this has introduced any spurious ‘variability’ into our data set.

Fig. 8 plots the debiased variability index against flux density. Although several of the strongest sources in our sample are also highly variable (in particular 0623−6436, 1546−6837 and 1903−6749 in Table 3), there appears to be no strong correlation between variability and flux density for the sample as a whole. For example, the generalized Kendall's tau correlation implemented in the asurv statistical package for censored data (Isobe, Feigelson & Nelson 1986) has a value of 1.66, corresponding to a probability of 9.7 per cent that no correlation is present. Table 6 shows the distribution of the debiased variability index measured for sources in Table 3 over a one-year time-span from 2003 October to 2004 October. The majority of sources (58 per cent) vary by less than 10 per cent in 20 GHz flux density over this period, and only five sources varied by more than 30 per cent. The median debiased variability index at 20 GHz is 6.9 per cent.

Figure 8

Debiased variability index at 20 GHz, measured from 2003 to 2004 for 121 sources observed at both epochs. Variability of 6 per cent or more over this one-year interval is detectable in the current data set.

Figure 8

Debiased variability index at 20 GHz, measured from 2003 to 2004 for 121 sources observed at both epochs. Variability of 6 per cent or more over this one-year interval is detectable in the current data set.

Table 6

Distribution of the debiased variability index at 20 GHz for radio sources in our sample.

Debiased variability (per cent) n Fraction (per cent) 
<10 63 58 ± 7 
10–20 29 27 ± 5 
20–30 11 10 ± 3 
>30 5 ± 2 
Total 108  
Debiased variability (per cent) n Fraction (per cent) 
<10 63 58 ± 7 
10–20 29 27 ± 5 
20–30 11 10 ± 3 
>30 5 ± 2 
Total 108  

7 SOURCES DETECTED BY WMAP

Table 7 lists the sources in our sample which were also detected by the WMAP satellite (Bennett et al. 2003) at up to five frequencies between 23 and 94 GHz. All 12 WMAP sources with Galactic latitude |b| > 10° in the Dec. zone −60° to −70° were detected in our 20-GHz survey, and Fig. 9 shows that there is generally good agreement between the 23 GHz flux densities measured by WMAP and the 20 GHz values measured in this study. Of the 10 sources in our survey with S20 > 1 Jy, nine are also detected by WMAP at 23 GHz. The sole exception is 0623−6436, a Seyfert 1 galaxy which appears to be strongly variable at 20 GHz (it has a variability index of 43 per cent in Table 3).

Table 7

WMAP sources at Dec. −60° to −70°, and with Galactic latitude |b| > 10°. The five WMAP frequency bands are K (23 GHz), Ka (33 GHz), Q (41 GHz), V (61 GHz) and W (94 GHz), and the flux densities are from Bennett et al. (2003). Only one of our sources (J2035−6846) was detected by WMAP at 94 GHz, so W-band data are not included in this table. αH is the 8–20 GHz spectral index measured in this paper (see Section 4), and αWMAP is the WMAP spectral index quoted by Bennett et al. (2003).

Name WMAP catalogue no. S20 ATCA (Jy) S23WMAP (Jy) S33 S41 S61 αH αWMAP Polarization (per cent) Variability (per cent) 
0303–6211 162 1.26 ± 0.09 1.5 ± 0.1 1.6 ± 0.2 1.5 ± 0.2 1.7 ± 0.3 −0.51 ± 0.12 +0.1 ± 0.4 2.5 <6.0 
0309−6058 160 1.15 ± 0.08 1.3 ± 0.1 – – 1.6 ± 0.5 −0.04 ± 0.12 +0.2 ± 0.8 0.8 <6.0 
0506−6109 154 1.82 ± 0.12 2.9 ± 0.09 2.4 ± 0.1 2.0 ± 0.2 1.5 ± 0.3 +0.09 ± 0.12 −0.4 ± 0.3 1.2 <6.0 
0546−6415 156 0.36 ± 0.03 0.8 ± 0.06 0.6 ± 0.09 0.6 ± 0.1 – +0.25 ± 0.13 −0.6 ± 0.8 <0.6 22.5 
0743−6726 161 1.07 ± 0.08 1.6 ± 0.1 1.0 ± 0.1 1.0 ± 0.2 – −0.38 ± 0.12 −1.1 ± 0.6 4.8 <6.0 
1703−6212 198 1.29 ± 0.09 1.9 ± 0.1 2.0 ± 0.2 2.3 ± 0.2 2.0 ± 0.3 +0.83 ± 0.13 +0.1 ± 0.3 0.5 <6.0 
1723−6500 196 2.82 ± 0.20 2.1 ± 0.1 2.0 ± 0.2 1.6 ± 0.2 – +0.02 ± 0.12 −0.3 ± 0.4 <1.7 <6.0 
1803−6507 199 1.31 ± 0.09 1.2 ± 0.1 1.4 ± 0.2 1.5 ± 0.2 1.2 ± 0.3 +0.53 ± 0.12 +0.2 ± 0.5 0.8 <6.0 
1819−6345 200 1.83 ± 0.13 1.7 ± 0.1 1.2 ± 0.2 1.1 ± 0.2 1.4 ± 0.5 – −0.7 ± 0.5 0.8 – 
2035−6846 194 0.46 ± 0.03 1.0 ± 0.2 1.3 ± 0.2 0.9 ± 0.2 – −0.18 ± 0.13 +0.4 ± 0.6 4.2 9.8 
2157−6941 190 1.99 ± 0.11 3.6 ± 0.1 2.9 ± 0.2 2.6 ± 0.2 2.2 ± 0.4 – −0.6 ± 0.2 2.4 – 
2359−6052 187 >0.9 1.8 ± 0.1 – 1.3 ± 0.1 – – −0.5 ± 0.5 5.2 – 
Name WMAP catalogue no. S20 ATCA (Jy) S23WMAP (Jy) S33 S41 S61 αH αWMAP Polarization (per cent) Variability (per cent) 
0303–6211 162 1.26 ± 0.09 1.5 ± 0.1 1.6 ± 0.2 1.5 ± 0.2 1.7 ± 0.3 −0.51 ± 0.12 +0.1 ± 0.4 2.5 <6.0 
0309−6058 160 1.15 ± 0.08 1.3 ± 0.1 – – 1.6 ± 0.5 −0.04 ± 0.12 +0.2 ± 0.8 0.8 <6.0 
0506−6109 154 1.82 ± 0.12 2.9 ± 0.09 2.4 ± 0.1 2.0 ± 0.2 1.5 ± 0.3 +0.09 ± 0.12 −0.4 ± 0.3 1.2 <6.0 
0546−6415 156 0.36 ± 0.03 0.8 ± 0.06 0.6 ± 0.09 0.6 ± 0.1 – +0.25 ± 0.13 −0.6 ± 0.8 <0.6 22.5 
0743−6726 161 1.07 ± 0.08 1.6 ± 0.1 1.0 ± 0.1 1.0 ± 0.2 – −0.38 ± 0.12 −1.1 ± 0.6 4.8 <6.0 
1703−6212 198 1.29 ± 0.09 1.9 ± 0.1 2.0 ± 0.2 2.3 ± 0.2 2.0 ± 0.3 +0.83 ± 0.13 +0.1 ± 0.3 0.5 <6.0 
1723−6500 196 2.82 ± 0.20 2.1 ± 0.1 2.0 ± 0.2 1.6 ± 0.2 – +0.02 ± 0.12 −0.3 ± 0.4 <1.7 <6.0 
1803−6507 199 1.31 ± 0.09 1.2 ± 0.1 1.4 ± 0.2 1.5 ± 0.2 1.2 ± 0.3 +0.53 ± 0.12 +0.2 ± 0.5 0.8 <6.0 
1819−6345 200 1.83 ± 0.13 1.7 ± 0.1 1.2 ± 0.2 1.1 ± 0.2 1.4 ± 0.5 – −0.7 ± 0.5 0.8 – 
2035−6846 194 0.46 ± 0.03 1.0 ± 0.2 1.3 ± 0.2 0.9 ± 0.2 – −0.18 ± 0.13 +0.4 ± 0.6 4.2 9.8 
2157−6941 190 1.99 ± 0.11 3.6 ± 0.1 2.9 ± 0.2 2.6 ± 0.2 2.2 ± 0.4 – −0.6 ± 0.2 2.4 – 
2359−6052 187 >0.9 1.8 ± 0.1 – 1.3 ± 0.1 – – −0.5 ± 0.5 5.2 – 
Figure 9

Comparison of our 20 GHz flux densities with the 23 GHz flux densities measured by WMAP for sources in common. The two filled circles show the objects for which we measured flux-density variability over the period 2003–04, as discussed in Section 5.

Figure 9

Comparison of our 20 GHz flux densities with the 23 GHz flux densities measured by WMAP for sources in common. The two filled circles show the objects for which we measured flux-density variability over the period 2003–04, as discussed in Section 5.

8 DISCUSSION AND CONCLUSIONS

Our aim in this paper has been to present some first results on the polarization and variability of radio sources selected at 20 GHz, and to outline some methodology which will also be useful in analysing data from the much larger ATCA 20 GHz (AT20G) survey which is now in progress. We now summarize and discuss the main results from our pilot survey of 173 sources selected to have flux densities above 100 mJy at 20 GHz.

8.1 Radio-source populations at 20 GHz

8.1.1 Comparison with surveys at 15 GHz

Our survey is complementary to the recent 15 GHz studies of Taylor et al. (2001) and Bolton et al. (2004), since we cover a significantly larger area of sky, but at a somewhat higher flux-density level. It is therefore interesting to compare some of our results with those in the 15-GHz surveys.

In Section 5, we used a radio two-colour diagram to characterize the spectra of sources selected at 20 GHz, and showed that most of these sources have significant spectral curvature over the range 0.8–20 GHz. Similar results were found by Bolton et al. (2004), who studied the 1.4–43 GHz radio spectra of 176 sources detected at 15 GHz in a blind survey of about 200 deg2 of sky. Bolton et al. (2004) found that 20–30 per cent of their sources had rising spectra at 1–5 GHz, with the fraction increasing to 39 per cent for sources with S15 > 150 mJy. Many of these sources had a spectral peak (turnover) above 5 GHz. For our sample selected at 20 GHz, 39 per cent of sources with S20 > 100 mJy have rising spectra between 0.8 and 5.0 GHz (i.e. αL > 0.1 in Table 5), with the majority of these showing a spectral peak above 5 GHz. Radio sources selected at 20 GHz therefore appear to have similar spectral properties to sources selected at the slightly lower frequency of 15 GHz.

As noted in Section 3.5, the optical identification rate for sources selected at 20 GHz is significantly higher than has been found in surveys to similar flux limits at 1.4 GHz. In contrast to low frequencies, where the strongest radio sources are mostly distant, powerful radio galaxies (e.g. Jackson & Wall 1999), the strongest sources at 20 GHz appear to be mainly QSOs. A direct comparison with the optical results of Bolton et al. (2004) is not completely straightforward, since they made most of their optical identifications in the R band rather than B band, and did not explicitly distinguish between galaxies and candidate QSOs. However, we can directly compare our overall identification rate on the blue SuperCOSMOS DSS images with that found by Bolton et al. (2004) in the blue Palomar O-band DSS images, as shown in Table 8. Our results confirm the trend found by Bolton et al. (2004) for brighter 15–20 GHz sources to have a higher optical ID rate and brighter optical counterparts.

Table 8

Comparison of the optical properties of radio sources selected in high-frequency flux-limited surveys. The 15 GHz values are from Bolton et al. (2004) and the 20 GHz data from this paper.

Frequency Flux density Median Fraction with an optical 
(GHz) limit b mag ID at b < 21 mag (per cent) 
15 >25 mJy 21.6 52 ± 7 (64/124) 
15 >60 mJy 20.9 61 ± 9 (43/70) 
20 >100 mJy 19.8 82 ± 8 (118/144) 
20 >500 mJy 18.9 93 ± 19 (25/27) 
Frequency Flux density Median Fraction with an optical 
(GHz) limit b mag ID at b < 21 mag (per cent) 
15 >25 mJy 21.6 52 ± 7 (64/124) 
15 >60 mJy 20.9 61 ± 9 (43/70) 
20 >100 mJy 19.8 82 ± 8 (118/144) 
20 >500 mJy 18.9 93 ± 19 (25/27) 

8.1.2 Comparison with predictions from low-frequency studies

Taylor et al. (2001) have noted that, as a result of spectral curvature, the radio-source population at 15 GHz cannot be reliably predicted by extrapolation from surveys at frequencies of 1–5 GHz. Of the sources they expected to detect at 15 GHz, based on extrapolation of the spectral index measured from the NVSS catalogue at 1.4 GHz and GB6 catalogue at 5 GHz, only 45 per cent (55/122) were actually seen. Furthermore, roughly 10 per cent of the sources they detected at 15 GHz were not predicted by this method.

We attempted to predict the observed source population in our survey region above 100 mJy at 20 GHz by extrapolating the radio spectral indices measured from the 0.84 GHz SUMSS and 4.85 GHz PMN surveys. For a subset of our survey area covering about 250 deg2 well away from the Galactic plane, we detected 33 per cent (28/84) of the sources predicted from extrapolation of the 0.8–5 GHz spectral indices. Conversely, 18 per cent (6/34) of the sources we actually detected at 20 GHz were not predicted by the low-frequency extrapolation. We therefore confirm the findings of Taylor et al. (2001) that neither the existence nor the flux density of a 15–20 GHz source can be reliably predicted by extrapolating the results of surveys at lower frequencies, and show that this is also the case at higher flux densities than were probed by the Taylor et al. (2001) survey.

8.1.3 Phase calibrators for ALMA?

The results of the previous section are relevant to the planned calibration strategy for the ALMA millimetre array now under construction in Chile. ALMA will operate at 90–720 GHz, and the aim is to calibrate the data by fast-switching between a program source and a calibrator less than 1°–2° away. The surface density of currently known calibrators at 90 GHz is far lower than this, so large numbers of new calibrators will need to be found. The currently planned strategy for this (Holdaway, Carilli & Laing 2004) is to select candidates by extrapolation from existing 1–5 GHz source catalogues. Our results, and those of Taylor et al. (2001) imply that such a strategy has at best a 30 per cent success rate in selecting sources at 20 GHz, and that the success rate at 90 GHz may be far lower.

A recent pilot study at 90–100 GHz of a subset of sources detected in our 20 GHz survey shows that the ATCA can measure accurate continuum flux densities down to levels well below 100 mJy, and that the 8–20 GHz radio spectral index may be a good predictor of the observed flux density at 90 GHz (Sadler et al., in preparation). We therefore suggest that the 20 GHz source catalogues now being produced for the whole southern sky (Dec. δ < 0°) in the AT20G survey will provide a more efficient way of identifying 90 GHz phase calibrators for ALMA than the currently proposed technique of extrapolation from radio surveys at 1–5 GHz.

8.1.4 ‘Flat-spectrum’ and ‘steep-spectrum’ populations

Earlier in this paper, we characterized the 20 GHz sources in terms of their position in the radio two-colour diagram shown in Fig. 7. This makes clear both the diversity of radio spectra seen in high-frequency sources and the difficulty of predicting high-frequency properties from low-frequency spectra. Studies of the cosmic evolution of radio sources, however, usually consider only two source populations – extended, steep-spectrum sources and compact, flat-spectrum sources. As discussed by Peacock (1985) these two populations can be understood physically, with the radio flux density being dominated by emission from extended radio lobes in steep-spectrum sources and a central compact core in flat-spectrum sources. In a sample selected at low frequency, the physically distinct optically thin diffuse emission has a distribution of spectral indices centred at −0.7 and so the dividing line between ‘flat’ and ‘steep-spectrum’ sources is traditionally set at a spectral index of α=−0.5. We note, however, that this division will be somewhat frequency dependent.

Radio-source samples selected at higher frequencies are increasingly dominated by flat-spectrum sources which are expected to be compact in nature. Even at 20 GHz, however, there is a minority population of objects which would be considered steep-spectrum using the normal convention of α < −0.5 at frequencies of 1–5 GHz. In terms of the overall properties of our sample, and as a guide for later comparison with other studies, it is therefore useful to note that our 20 GHz sample contains roughly 87 per cent ‘flat-spectrum’ and 13 per cent ‘steep-spectrum’ as defined by their low-frequency spectral index (αL in Table 5).

8.2 Polarization properties at 20 GHz

The high selection frequency of our survey makes it particularly useful for estimating the contribution of foreground radio sources to future studies of polarization fluctuations in the CMB radiation at 20 GHz and above.

Fig. 10 plots the fractional linear polarization measured at 20 GHz against the 20 GHz flux density, and shows that most sources selected at 20 GHz have low levels of linear polarization (typically 1–5 per cent). The median fractional polarization at 20 GHz is 2.3 per cent, but Fig. 10 suggests that there is a trend for fainter 20 GHz sources to show higher levels of polarization (the median linear polarization is 2.7 per cent for sources with 100 < S20 < 200 mJy and 1.7 per cent for sources with S20 > 200 mJy). A generalized Kendall's tau correlation test for censored data (Isobe et al. 1986) gives a value of 2.07, corresponding to a 3.9 per cent probability that the observed correlation is due to chance. Fig. 11 shows that the maximum polarized flux densities measured are 40–50 mJy, and so sources bright enough to calibrate CMB polarization experiments are rare.

Figure 10

Fractional linear polarization at 20 GHz, measured in 2004. Open triangles show upper limits for sources where no polarized flux was detected.

Figure 10

Fractional linear polarization at 20 GHz, measured in 2004. Open triangles show upper limits for sources where no polarized flux was detected.

Figure 11

Total linearly polarized flux density at 20 GHz, plotted as a function of the total flux density. As in Fig. 10, open triangles show upper limits for sources where no polarized flux was detected. Note that although the weaker 20 GHz sources in our sample typically have higher fractional polarization, the strongest sources still dominate the source counts in polarized flux.

Figure 11

Total linearly polarized flux density at 20 GHz, plotted as a function of the total flux density. As in Fig. 10, open triangles show upper limits for sources where no polarized flux was detected. Note that although the weaker 20 GHz sources in our sample typically have higher fractional polarization, the strongest sources still dominate the source counts in polarized flux.

The median fractional polarization of 2.3 per cent which we measure at 20 GHz for a flux-limited sample with S20 > 100 mJy is very close to the median value of 2.2 per cent found by Mesa et al. (2002) for a flux-limited sample at 1.4 GHz with S1.4 > 80 mJy. Mesa et al. (2002) also observed a marginally significant trend for weaker sources to have a higher median polarization.

The similarity between the median polarizations observed at 1.4 and 20 GHz is somewhat surprising, since the 1.4 GHz sample is overwhelmingly dominated by steep-spectrum sources and the 20 GHz sample by flat-spectrum sources. Mesa et al. (2002) find a similar median polarization at 1.4 GHz for both steep- and flat-spectrum sources, and Tucci et al. (2004) argued that the mean level of polarization in flat-spectrum radio sources increases steadily with frequency. We might therefore have expected the median polarization in our sample to be higher than that observed at 1.4 GHz.

This does not appear to be the case, and a larger data set at 20 GHz is needed both to examine this issue in more detail and to compare the high-frequency polarization properties of the different spectral subclasses identified in Section 5 of this paper.

8.3 Variability of the source population at 20 GHz

In Section 6 of this paper we showed that the general level of variability of radio sources selected at 20 GHz sources appears to be low, with a median variability index of 6.9 per cent on a one-year time-scale (see Table 6). In the current sample, we find no significant correlation between the variability index of a source and its fractional polarization or radio spectral index. This is perhaps not surprising, since our sample is relatively small, and only a few of the sources are strongly variable.

The five most variable sources in our sample (with a variability index of 30 per cent or more) are J0507−6104, J0623−6436, J0820−6814, J1546−6837 and J1903−6749. Four of these are candidate QSOs of unknown redshift and one (J0623−6436) is a Seyfert galaxy at redshift z= 0.129. None of these radio sources appear to have been monitored previously, so nothing is known about their long-term behaviour.

Direct comparison of our results with previous studies is difficult, both because many of these studies are based on targeted rather than flux-limited samples, and because we have so far only analysed data from two measurements taken a year apart. The variability time-scales measured in this paper are all in the observed frame. The redshifts z of many of our sources are currently unknown, and we remind the reader that the observed variability time-scale will differ from the intrinsic value by a factor of (1 +z) so that longer monitoring is particularly important for the highest redshift sources.

Even at this stage, however, we can conclude that the general level of variability in sources selected at 20 GHz appears to be low on time-scales of 1–2 yr, and that source catalogues made at this frequency should therefore be robust on time-scales of at least a few years. Long-term monitoring studies of targeted sources by Valtaoja and co-workers (e.g. Valtaoja et al. 1988) show that even though many high-frequency sources have bursts of short-term variability, they are relatively quiescent for most of the time. This is entirely consistent with our results, and suggests that we should continue to monitor this source sample for a much longer period of time.

8.4 Conclusions

The pilot-study results presented here show that a sensitive 20 GHz radio continuum survey of the whole southern sky is feasible, and should produce a uniform source catalogue which is largely stable over time-scales of a few years. Such a survey should provide further insights into the nature of the high-frequency radio-source population, both in its own right and as a polarized foreground component in future CMB experiments like Planck.

We acknowledge financial support from the Australian Research Council (ARC) through the award of a Federation Fellowship to RDE and an ARC Australian Professorial Fellowship to EMS. This research has made use of the NED which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We thank the referee, Prof. Ian Browne, for a number of helpful suggestions.

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Appendix

APPENDIX A: NOTES ON INDIVIDUAL SOURCES IN Table 3

J0025−6028

Double source with 23 arcsec separation, PA 159°.

J0103−6439

Wide double at 843 MHz, with 3.5 arcmin separation Only the core is seen at 20 GHz.

J0121−6309

Core plus 39 arcsec double, PA 14°.

J0257−6112

Core plus 10 arcsec jet, PA ∼60°.

J0425−6646

This source was identified by Ricci et al. (2004a) with a magnitude 16.8 stellar object. The higher resolution radio image we obtained in 2004 makes it clear that the correct ID is a fainter stellar object slightly to the west.

J0715−6829

This source lies close to a bright (11th magnitude) foreground star, and no optical identification is possible from the SuperCOSMOS optical images.

J0743−6726

Core plus 12 arcsec jet, PA 117°.

J1807−7012

Double source with 27 arcsec separation, PA 114°, no core visible.

J1822−6359

Double source with 32 arcsec separation, PA 57°.

J1824−6717

Double source with 49 arcsec separation, PA 158°, no core visible.

J2157−6941

Core plus wide double source with 1.5 arcmin separation, PA 20°. Some flux may be missing at 18 and 20 GHz. This source has been studied in detail by Fosbury et al. (1998).

J2306−6521

Jackson et al. (2002) identify this source with a faint (B= 24 mag) galaxy, for which they measure the quoted redshift of z= 0.470.

J2358−6052 and J2350−6057

Hotspots of the powerful radio galaxy PKS2356−61, as discussed by Ricci et al. (2004a).