VLBI Observations of Southern Hemisphere ICRF Sources. I.

Ojha, R.; Fey, A. L.; Johnston, K. J.; Jauncey, D. L.; Reynolds, John E.; Tzioumis, A. K.; Quick, J.; Nicolson, G. D.; Ellingsen, S. P.; Dodson, Richard; McCulloch, P. M.

doi:10.1086/421001

Cited by 53 publications

(78 citation statements)

References 23 publications

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“…A weak radio continuum component is also observed (at the 5% level) between the two major lobes in the 2.3 GHz image, which corresponds to a 15σ detection. Interestingly, 8.4 GHz VLBI observations (Ojha et al 2004) confirm the presence and prominence of this component at high frequency, suggesting this component is likely to be the radio core in PKS 1814-637 (see Fig. 1 right).…”

Section: The Ism Of Pks 1814: Spitzer Mid-ir Datamentioning

confidence: 86%

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PKS 1814-637: a powerful radio-loud AGN in a disk galaxy

Morganti

Holt

Tadhunter

et al. 2011

A&A

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We present a detailed study of PKS 1814-637, a rare case of powerful radio source (P 5 GHz = 4.1 × 10 25 W Hz −1 ) hosted by a disk galaxy. Optical images have been used to model the host galaxy morphology confirming it to be dominated by a strong (and warped) disk component that is observed close to edge-on to the line of sight. This is the first radio galaxy found to reside in a disk dominated galaxy with radio luminosity equivalent to powerful FRII objects. At radio wavelengths, PKS 1814-637 is about 480 pc in diameter and it is classified as a compact steep spectrum (CSS) source; such sources are usually considered to be radio sources observed in the early stages of their evolution. However, the optical and mid-IR spectroscopic properties of PKS1814-637 show more in common with Seyfert galaxies than they do with radio galaxies, with the detection of H 2 , and PAH emission features, along with HI and silicate absorption features, providing evidence for a rich ISM which is likely to be related to the disk morphology of the host galaxy. We argue that the interaction between the radio plasma and the rich ISM in this and similar objects may have boosted their radio emission, allowing them to more easily enter flux limited samples of radio sources. In this case, PKS 1814-637 represents a type of "imposter": an intrinsically low power object that is selected in a radio flux limited sample because of the unusually efficient conversion of jet power into radio emission. This would make PKS 1814-637 an extreme example of the effects of jet-cloud interactions in galaxies containing a rich ISM, and perhaps a missing link between radio galaxies and radio-loud Seyfert galaxies. However, it is unlikely that jet-cloud interactions alone can account for the unusually powerful radio emission compared to Seyfert galaxies, and it is probable that the jet in PKS 1814-637 is also intrinsically more powerful than in typical Seyfert galaxies, perhaps due to a higher bulge and black hole mass. The estimated BH mass is indeed higher than the majority of Seyfert galaxies in the local Universe. We speculate that sources similar to PKS1814-637 are likely to be more common at high redshifts, because of the enhanced probability at earlier epochs of triggering radio sources in moderately massive bulges that are also gas-rich.

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Section: The Ism Of Pks 1814: Spitzer Mid-ir Datamentioning

confidence: 86%

“…(Tzioumis et al 2002) with the 8.4 GHz (i.e. high resolution) image from Ojha et al 2004) superimposed. This overlay illustrates the presence of a compact component (SE of the brighter lobe) that becomes prominent in the high frequency observations: we identify this component with the radio core.…”

Section: Host Galaxy Morphologymentioning

confidence: 99%

PKS 1814-637: a powerful radio-loud AGN in a disk galaxy

Morganti

Holt

Tadhunter

et al. 2011

A&A

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“…Abdo et al (2010) show a light curve with two flaring events, occurring around February and June 2009 respectively. Previous VLBI observations have found the source to be strongly core dominated on the milli-arcsecond scale (Ojha et al 2010(Ojha et al , 2004Piner et al 2007). On the kilo-parsec scale, ATCA imaging shows some extended structure (Marshall et al 2005;Burgess & Hunstead 2006) extending over 4 arcsec.…”

Section: Resultsmentioning

confidence: 96%

“…Ojha et al 2004) augmented by telescopes in South Africa, Chile, Antarctica and New Zealand. This array allows the imaging of the southern sky at milliarcsecond scale or better resolution on a regular basis (e.g., Müller et al 2011).…”

Section: Introductionmentioning

confidence: 99%

High resolution rapid response observations of compact radio sources with the Ceduna Hobart Interferometer (CHI)

Blanchard

Lovell

Ojha

et al. 2012

A&A

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Context. Frequent, simultaneous observations across the electromagnetic spectrum are essential to the study of a range of astrophysical phenomena including active galactic nuclei. A key tool of such studies is the ability to observe an object when it flares i.e. exhibits a rapid and significant increase in its flux density. Aims. We describe the specific observational procedures and the calibration techniques that have been developed and tested to create a single baseline radio interferometer that can rapidly observe a flaring object. This is the only facility that is dedicated to rapid high resolution radio observations of an object south of −30 degrees declination. An immediate application is to provide rapid contemporaneous radio coverage of AGN flaring at γ-ray frequencies detected by the Fermi Gamma-ray Space Telescope. Methods. A single baseline interferometer, the Ceduna Hobart Interferometer (CHI), was formed with radio telescopes in Hobart, Tasmania and Ceduna, South Australia. A software correlator was set up at the University of Tasmania to correlate these data. Results. Measurements of the flux densities of flaring objects can be made using our observing strategy within half an hour of a triggering event. These observations can be calibrated with amplitude errors better than 15%. Lower limits to the brightness temperatures of the sources can also be calculated using CHI.

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“…It will thus be crucial in the future to unveil more high-quality optically-bright radio sources suitable for the Gaia link beyond those currently identified from the ICRF and reported in Table 3. A first opportunity to find such sources may come from the second generation of the ICRF (ICRF-2), currently under development, which will improve the position accuracy of the current ICRF sources and provide VLBI positions of additional sources. This new frame will rely on data acquired by international observing programs organized through the International VLBI Service for Geodesy and Astrometry (Schluter & Behrend 2007) or other programs such as that developed in the southern hemisphere by the United States Naval Observatory (Ojha et al 2004(Ojha et al , 2005. Another option would be to use the Very Long Baseline Array (VLBA) Calibrator Survey (VCS), which comprises milliarcsecond accurate positions for about 3000 additional sources along with images for a large fraction of those sources (Beasley et al 2002;Fomalont et al 2003;Petrov et al 2005Petrov et al , 2006Kovalev et al 2007;Petrov et al 2008).…”

Section: Discussionmentioning

confidence: 99%

Astrometric suitability of optically-bright ICRF sources for the alignment with the future Gaia celestial reference frame

Bourda¹,

Charlot²,

Campion³

2008

A&A

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Context. The International Celestial Reference Frame (ICRF), currently based on the position of 717 extragalactic radio sources observed by VLBI (Very Long Baseline Interferometry), is the fundamental celestial reference frame adopted by the International Astronomical Union (IAU) in 1997. Within the next 10 years, the European space astrometry mission Gaia, to be launched by 2011, will permit determination of the extragalactic reference frame directly in the visible for the first time. Aligning these two frames with the highest accuracy will therefore be very important in the future for ensuring consistency between the measured radio and optical positions.Aims. This paper is aimed at evaluating the current astrometric suitability of the individual ICRF radio sources which are considered appropriate for the alignment with the future Gaia frame. Methods. To this purpose, we cross-identified the ICRF and the optical catalog (Véron-Cetty & Véron, 2006, A&A, 455, 773), in order to identify the optically-bright ICRF sources that will be positioned with the highest accuracy with Gaia. Then we investigated the astrometric suitability of these sources by examining their VLBI brightness distribution. Results. We identified 243 candidate ICRF sources for the alignment with the Gaia frame (i.e. with an optical counterpart brighter than the apparent magnitude 18), but only 70 of these (i.e. only 10% of the ICRF sources) are found to have the necessary high astrometric quality (i.e. a brightness distribution that is compact enough) for this link. Additionally, it was found that the QSOs (quasi stellar objects) that will have the most accurate positions in the Gaia frame tend to have less-accurate VLBI positions, most probably because of their physical structures. Conclusions. Altogether, this indicates that identifying other high-quality VLBI radio sources suitable for the alignment with the future Gaia frame is mandatory.

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VLBI Observations of Southern Hemisphere ICRF Sources. I.

Cited by 53 publications

References 23 publications

PKS 1814-637: a powerful radio-loud AGN in a disk galaxy

PKS 1814-637: a powerful radio-loud AGN in a disk galaxy

High resolution rapid response observations of compact radio sources with the Ceduna Hobart Interferometer (CHI)

Astrometric suitability of optically-bright ICRF sources for the alignment with the future Gaia celestial reference frame

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