Free Access
Issue
A&A
Volume 526, February 2011
Article Number A74
Number of page(s) 20
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361/201015406
Published online 23 December 2010

Online material

Appendix B: Notes on individual sources

  • S329: this source appears to be mildly resolved in our VLBIimage, and is undetected at 0.5–8 keV byLehmer et al. (2005). Its redshift is1.00 (Mainieri et al. 2008).

  • S331: this source has been classified as AGN because of its more than tenfold radio excess over the radio-infrared relation. Its value of q24 is −1.96 which clearly puts it into the AGN regime. Its X-ray properties (Lehmer et al. 2005; Szokoly et al. 2004) suggest that it is a type 1 AGN.

  • S380: this compact radio object was classified as AGN based on its q24 value of −0.21 (Norris et al. 2006). Its X-ray properties qualify it as a galaxy because its X-ray luminosity in the 0.5–8 keV band is only LX = 4.6 × 1031 W (Lehmer et al. 2005; Szokoly et al. 2004). It has a spectral index of −0.6 (Kellermann et al. 2008) and a redshift of 0.02 (Wolf et al. 2004), making it the closest object in our sample.

  • S393: this is the only VLBI-detected source with a pronounced extension in the VLBI observations. It is an X-ray source at a redshift of 1.07 (Zheng et al. 2004), and it has been identified as AGN by Norris et al. (2006) because of its X-ray hardness ratio. The Szokoly et al. (2004) criteria result in a type 2 AGN classification, and its radio spectral index is −1.2 (Kellermann et al. 2008). Only a very small fraction (5%) of its arcsec-scale flux density is recovered in the VLBI observations. At its redshift, the angular separation of 32 mas of the two components seen in our VLBI images translate to a projected distance of 263 pc, and is therefore in the regime of GPS sources (and is of a size comparable to the narrow-line region).

  • S404: the VLBI images of this source display almost all the flux density found in the ATCA observations. It has a compact morphology and its X-ray properties classify it as a type 1 QSO (Luo et al. 2008; Szokoly et al. 2004). It has a spectral index of 0.0 (Kellermann et al. 2008), indicating a compact, self-absorbed radio source, and its redshift is 0.54 (Norris et al. 2006). The HST images show an unresolved object with diffraction spikes, indicative of a point-like optical source. Its q24, however, is 0.31 which is only a mild radio excess over the radio-infrared relation.

  • S411: this is a compact source – all arcsec-scale emission is recovered in the VLBI image. Its hardness ratio of −0.44 and X-ray luminosity qualify it as a type 1 QSO (Luo et al. 2008; Szokoly et al. 2004) and it is located at a redshift of 1.61 (Afonso et al. 2006). It has a spectral index of −0.5 (Kellermann et al. 2008), and it is a featureless, round object in the HST ACS images (Giavalisco et al. 2004).

  • S414: this is a compact source – the VLBI observations recover 95% of the flux density measured with the ATCA (Norris et al. 2006). It has q24 = −0.29 which makes this an AGN. S414 has a redshift of 1.57 (Mainieri et al. 2008) and is the brightest X-ray source in our sample, with LX = 1.5 × 1038 W (0.5–8 keV), qualifying it as a type 1 QSO (Lehmer et al. 2005; Szokoly et al. 2004).

  • S421: the radio data for this source are consistent with a point source since it is unresolved in our VLBI image. It is not an X-ray source, and it has a spectral index of −0.6 (Kellermann et al. 2008) and a redshift of 0.13 (Mainieri et al. 2008).

  • S423: this compact radio source is classified as a normal galaxy using the scheme by Szokoly et al. (2004). It has a spectral index of −0.2 (Kellermann et al. 2008) and a redshift of 0.73 (Afonso et al. 2006). Afonso et al. report spectroscopic evidence for star-forming activity in this galaxy, potentially merging with a nearby (0.5′′) object. They identify five objects closer than 30′′ with similar redshifts. Mobasher et al. (2004) classify this object as an elliptical galaxy, using photometry in 17 bands. Hence there is no evidence except the VLBI detection that this object harbours an AGN. Given its redshift it has a 5 GHz radio luminosity of 7.5 × 1023   W   Hz-1, which is about an order of magnitude too low to classify it as a radio-loud object, and is more typical of Seyferts.

  • S437: this source has been classified as AGN based on q24 and the literature (Norris et al. 2006). Only 4% of its ATCA flux density were recovered, and the VLBI images show an unresolved source. Yet it is a powerful X-ray source exceeding a luminosity of 1037 W (0.5–8 keV) and it has a hardness ratio of −0.48, indicating a type 1 QSO (Luo et al. 2008; Szokoly et al. 2004). The redshift of this object is 0.73 (Afonso et al. 2006). It is one of four objects covered by the Great Observatories Origins Deep Survey (GOODS, Giavalisco et al. 2004) with the Hubble Space Telescope. It is an unresolved object in all four bands, and diffraction spikes indicate a strong point-like component.

  • S443: this compact object is the faintest VLBI-detected radio source in our survey, with an arcsec-scale flux density of only 0.4 mJy (Norris et al. 2006). It is associated with a spiral galaxy, with a spectral index of −0.5 (Kellermann et al. 2008) and a redshift of 0.076 (Afonso et al. 2006). Its q24 value of 1.05 is broadly consistent with the value of 0.84 found by Appleton et al. (2004) for the radio-infrared relation, and also its X-ray properties suggest that it is a galaxy without AGN. Afonso et al. (2006) report that the X-ray emission comes from north of the galaxy nucleus, with indications of star-forming activity. Mobasher et al. (2004) classify it as an Sbc object based on 18-band photometry. We consider this a marginal detection, partly because the VLBI position places the VLBI source at the very edge of the visible perimeter of the galaxy, which can be treated as evidence against a detection (see Fig. 7). On the other hand, a radio transient cannot be ruled out (see Lenc et al. 2008). We also note that the radio luminosity of this source, 5 × 1021 W Hz-1, is similar to one of the brightest radio SNe, SN1986J. We therefore consider it possible that S443 is a radio supernova.

  • S447: this source has been classified as AGN based on q24 and also is an X-ray source. It has a spectroscopic redshift of 1.96 (Norris et al. 2006), where 1 mas corresponds to 8.5 pc. It is unresolved in our images, hence most of the VLBI flux density (20% of the arcsec-scale flux density) comes from a region smaller than  ~100 pc. It is the second most luminous X-ray source in our sample of 96 sources, with LX = 1.3 × 1038 W (0.5–8 keV, Lehmer et al. 2005). Nevertheless it has a soft spectrum with HR = −0.37 which qualifies it as a type 1 QSO (Szokoly et al. 2004).

  • S472: this is a very compact source since 93% of the ATCA flux density are seen in the VLBI image. Based on its q24 = −0.31 this is an AGN. There is conflicting information about its redshift: Zheng et al. (2004) give a photometric redshift of 1.22, but Le Fèvre et al. (2004) measured a spectroscopic redshift of 0.55, which we deem more reliable. Its X-ray spectrum is hard between 0.5–8 keV and indicates an absorbed type 2 AGN (Lehmer et al. 2005; Szokoly et al. 2004).

  • S474: this is a compact source which displays all of its ATCA flux density in a low-resolution VLBI image. Its redshift is 0.98 (Le Fèvre et al. 2004) and its spectral index is −1.4 (Kellermann et al. 2008). It is a faint infrared source and is undetected in the X-ray. This is the only VLBI-detected radio source which remained undetected by the 2 Ms Chandra exposure (Luo et al. 2008).

  • S482: this is a compact radio source. It is also an X-ray source (Lehmer et al. 2005) with hardness ratio −0.33, but its luminosity is only LX = 5.2 × 1033 W (0.5–8 keV), which then qualifies it as a galaxy (Szokoly et al. 2004). It was classified by Norris et al. (2006) as an AGN based on its q24 of −0.61. It has a spectral index of −0.5 (Kellermann et al. 2008) and redshift of 0.15 (Norris et al. 2006).

  • S500: this compact radio object has an absorbed X-ray spectrum with hardness ratio 0.6 (Lehmer et al. 2005) , and it is classified as a type 2 AGN by the Szokoly et al. (2004) criteria. It has a spectral index of −0.9 (Kellermann et al. 2008) and a redshift of 0.73 (Mainieri et al. 2008). Based on q24 = −0.21, this is an AGN.

  • S503: this is the brightest source in our VLBI observations, with a flux density of (21.2    ±    3.0)   mJy (compared to an ATCA flux density of 19.3 mJy). Hence this source is very compact, but our uniformly-weighted image indicates that its core is resolved into two components with a separation of around 10 mas (76 pc at the distance of S503; z = 0.81, Mainieri et al. 2008). It is an X-ray source indicating a type 1 AGN (Lehmer et al. 2005; Szokoly et al. 2004).

  • S517: this compact radio source is not a detected X-ray source, and it has a spectral index of −0.9 (Kellermann et al. 2008) and a redshift of 1.03 (Mainieri et al. 2008). The extensions towards the south-east seen in the VLBI images are imaging artifacts and do not indicate a true extension.

  • S519: this compact radio source has previously been classified as AGN based on its q24 = −0.42. It is not an X-ray source, and it has a redshift of 0.69 (Norris et al. 2006).

  • S520: this source is mildly resolved. From its arcsec-scale flux density of 3.7 mJy (2.5 ± 0.4)   mJy could be recovered in our lowest-resolution image. There is a hint of a  ~25 mas extension towards the south-west in the naturally and uniformly-weighted image which at the redshift of the source of 1.4 (Wolf et al. 2004) corresponds to around 200 pc. It has only a very faint IR counterpart in the co-located Spitzer image, and is not detected in the ECDFS survey by Lehmer et al. (2005) (it is outside the GOODS region).

  • S545: this compact radio source also does not exhibit X-ray emission, and neither a spectral nor a redshift are available.


© ESO, 2010

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