The influence of radio-extended structures on offsets between the optical and VLBI positions of sources in the ICRF2

Camargo, J. I. B.; Andrei, A. H.; Assafin, M.; Vieira-Martins, R.; Neto, D. N. da Silva

doi:10.1051/0004-6361/201016201

Cited by 8 publications

(8 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Four of their sources showed offsets relative to their ICRF2 positions larger than their 3σ confidence level, ∼80 mas. Camargo et al (2011) concluded that these separations cannot be explained merely by statistical fluctuations or systematic errors in the optical reference frame, and they might be related to the relatively more complex VLBI structure of the given quasars.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Optical-radio positional offsets for active galactic nuclei

Orosz

Frey²

2013

A&A

View full text Add to dashboard Cite

Context. It will soon become possible to directly link the most accurate radio reference frame with the Gaia optical reference frame using many common extragalactic objects. It is important to know the level of coincidence between the radio and optical positions of compact active galactic nuclei (AGNs). Aims. Using the best catalogues available at present, we investigate how many AGNs with significantly large optical-radio positional offsets exist as well as the possible causes of these offsets. Methods. We performed a case study by finding optical counterparts to the International Celestial Reference Frame (ICRF2) radio sources in the Sloan Digital Sky Survey (SDSS) Data Release 9 (DR9). The ICRF2 catalogue was used as a reference because the radio positions determined by Very Long Baseline Interferometry (VLBI) observations are about two orders of magnitude more accurate than the optical positions. Results. We find 1297 objects in common for ICRF2 and SDSS DR9. Statistical analysis of the optical-radio differences verifies that the SDSS DR9 positions are accurate to ∼55 milliarcseconds (mas) in both right ascension and declination, with no systematic offset with respect to ICRF2. We find 51 sources (∼4% of the sample) for which the positional offset exceeds 170 mas (∼3σ). Astrophysical explanations must exist for the majority of these outliers. There are three known strong gravitational lenses among them. Dual AGNs or recoiling supermassive black holes may also be possible. Conclusions. The most accurate Gaia-VLBI reference frame link will require a careful selection of a common set of objects by eliminating the outliers. On the other hand, the significant optical-radio positional non-coincidences may offer a new tool for finding e.g. gravitational lenses or dual AGN candidates. Detailed follow-up radio interferometric and optical spectroscopic observations are encouraged to investigate the outlier sources found in this study.

show abstract

Section: Discussionmentioning

confidence: 99%

“…The question of optical-radio positional differences was also investigated by Camargo et al (2011) using a different approach, with a smaller sample. They performed accurate relative optical astrometric measurements in the fields around 22 ICRF2 sources.…”

Section: Discussionmentioning

confidence: 99%

Optical-radio positional offsets for active galactic nuclei

Orosz

Frey²

2013

A&A

View full text Add to dashboard Cite

show abstract

“…Another important purpose concerns the few radio-loud, ICRF2 defining quasars, upon which will be established the orientation of the GCRF and its continuity to the ICRF. For these objects asymmetries between optical and radio morphology would induce spurious centroids offsets (Camargo et al 2011). On the same topic Zacharias & Zacharias (2014) brought up to the community for the first time the issue of the radio-optical offsets.…”

Section: Studies Of Morphologymentioning

confidence: 99%

LQAC-4: Fourth release of the Large Quasar Astrometric Catalogue

Gattano

Andrei

Coelho

et al. 2018

A&A

Self Cite

View full text Add to dashboard Cite

Context. From an astrometric point of view, quasars constitute the best and almost ideal reference objects in the celestial sphere, with a priori no significant proper motion. Since the third release of the Large Quasar Astrometric Catalogue (LQAC-3), a large number of quasars have been discovered, in particular those coming from the DR12Q release of the SDSS. Moreover, for cross-matched objects, we have taken advantage of the very accurate determinations of the quasars identified within the recent Gaia DR1 catalogue. Aims. Following the same procedure as in the three previous releases of the LQAC, our aim is to compile the large majority of all the quasars recorded so far. Our goal is to record their best coordinates and substantial information concerning their physical properties such as the redshift as well as multi-bands apparent and absolute magnitudes. Emphasis is given to the results of the cross-matches with the Gaia DR1 catalogue. Methods. New quasars coming from the DR12Q release were cross-matched with the precedent LQAC-3 compilation with a 1 search radius, in order to add the objects without counterpart to the LQAC-4 compilation. A similar cross-match was done with Gaia DR1 to identify the known quasars detected by Gaia. This enables one to improve significantly the positioning of these objects, and in parallel to study the astrometric performance of the individual catalogues of the LQAC-4 compilation. Finally, a new method was used to determine absolute magnitudes. Results. Our final catalogue, called LQAC-4, contains 443 725 objects. This is roughly 37.82% more than the number of objects recorded in the LQAC-3. Among them, 249 071 were found in common with the Gaia DR1, with a 1 search radius. That corresponds to 56.13% of the whole population in the compilation. Conclusions. The LQAC-4 delivers to the astronomical community a nearly complete catalogue of spectroscopically confirmed quasars (including a small proportion of compact AGNs), with the aim of giving their best equatorial coordinates with respect to the ICRF2 and with exhaustive additional information. For more than 50% of the sample, these coordinates come from the very recent Gaia DR1.

show abstract

“…However, these authors obtained inconsistent results. Camargo et al (2011); Zacharias & Zacharias (2014) reported that the optical-to-radio offset increases with the structure index, while Assafin et al (2013) did not detect any dependency. Zacharias & Zacharias (2014) found a negative correlation between the optical-to-radio offset and the redshift but this relation is not found in Orosz & Frey (2013).…”

Section: Cause Of Optical-to-radio Distancementioning

confidence: 94%

“…The frequency-dependent position of extragalactic objects is of interest in both astrometric and astrophysical fields, especially the position offset between the optical centroid and radio core. Results of studies of position frequency dependency can be used to improve accuracy of astrometric catalogues, for example, Aslan et al (2010); Camargo et al (2011); Assafin et al (2013); Shabala et al (2014). The study of optical-to-radio offset also provides a probing of the structural properties of Active Galactic Nucleus (AGNs), such as the accretion disc and relativistic jet (e.g., Orosz & Frey 2013;Plavin et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Comparison of multifrequency positions of extragalactic sources from global geodetic VLBI monitoring program and Gaia EDR3

Liu,

Lambert,

Charlot

et al. 2021

Preprint

View full text Add to dashboard Cite

Context. Comparisons of optical positions derived from the Gaia mission and radio positions measured by very long baseline interferometry (VLBI) probe the structure of active galactic nuclei (AGN) on the milli-arcsecond (mas) scale. So far, such comparisons have focused on using the S /X band (2/8 GHz) radio positions but have not taken advantage of the VLBI positions that exist at higher radio frequencies, namely K band (24 GHz) and X/Ka band (8/32 GHz). Aims. We extend previous works by considering two additional radio frequencies (K band and X/Ka band) with the aim to study the frequency dependence of the source positions and its potential connection with the physical properties of the underlying AGN. Methods. We compared the absolute source positions measured at four different wavelengths, that is, the optical position from the Gaia Early Data Release 3 (EDR3) and the radio positions at the dual S /X, X/Ka combinations and at K band, as available from the third realization of the International Celestial Reference Frame (ICRF3), for 512 common sources. We first aligned the three ICRF3 individual catalogs onto the Gaia EDR3 frame and compare the optical-to-radio offsets before and after the alignment. Then we studied the correlation of optical-to-radio offsets with the observing (radio) frequency, source morphology, magnitude, redshift, and source type. Results. The deviation among optical-to-radio offsets determined in the different radio bands is less than 0.5 mas, but there is statistical evidence that the optical-to-radio offset is smaller at K band compared to S /X band for sources showing extended structures. The optical-to-radio offset was found to statistically correlate with the structure index. Large optical-to-radio offsets appear to favor faint sources but are well explained by positional uncertainty, which is also larger for these sources. We did not detect any statistically significant correlation between the optical-to-radio offset and the redshift. Conclusions. The radio source structure might also be a major cause for the radio-to-optical offset. For the alignment of with the Gaia celestial reference frame, the S /X band frame remains the preferred choice at present.

show abstract

The influence of radio-extended structures on offsets between the optical and VLBI positions of sources in the ICRF2

Cited by 8 publications

References 31 publications

Optical-radio positional offsets for active galactic nuclei

Optical-radio positional offsets for active galactic nuclei

LQAC-4: Fourth release of the Large Quasar Astrometric Catalogue

Comparison of multifrequency positions of extragalactic sources from global geodetic VLBI monitoring program and Gaia EDR3

Contact Info

Product

Resources

About