Evidence of the<i>Gaia</i>–VLBI position differences being related to radio source structure

Mei-ling, XU; Lunz, Susanne; Anderson, J. M.; Savolainen, Tuomas; Zubko, Nataliya; Schuh, Harald

doi:10.1051/0004-6361/202040168

Cited by 20 publications

(18 citation statements)

References 39 publications

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“…Two sources (1538+149 and 2353+816) presenting particularly large X-to-O offsets are also ICRF3 defining sources. In several sources (0119+115, 0346+800, 0749+540, 0859+470, 1157−215, 1652+398, 1742−078, and 2223−052), the optical centroid is close to a radio jet feature (a particularity also recently supported by Xu et al 2021), suggesting that in such sources the optical emission is dominated by optically thin jet features in the downstream region of the jet. Such regions of synchrotron emission are expected to have a more organized magnetic field and higher linear polarization (e.g., Ginzburg 1979), which is supported by observations in radio Lister & Homan (2005) and optical Kovalev et al (2020).…”

Section: Analysis and Resultsmentioning

confidence: 54%

Parsec-scale alignments of radio-optical offsets with jets in AGNs from multifrequency geodetic VLBI, Gaia EDR3, and the MOJAVE program

Lambert

Liu

Arias

et al. 2021

A&A

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Aims. We aim to study the relative positions of quasar emission centers at different wavelengths in order to help link the various realizations of the International Celestial Reference System (ICRS), and to unveil systematic uncertainties and individual source behavior at different wavelengths. Methods. We based our study on four catalogs representing the ICRS, the ICRF3 positions in the three VLBI bands X, K, and Ka, and the Gaia EDR3 catalog in optical wavelengths. We complemented radio source positions with jet kinematics results from the MOJAVE team, allowing us to obtain jet directions on the sky. A six-parameter deformation model was used to remove systematic uncertainties present in the different catalogs. Results. For a set of 194 objects common to the four catalogs and to the objects whose jet kinematics was studied by the MOJAVE team, we computed the orientation between positions at the different wavelengths and with respect to the directions of the jets. We find that the majority of these objects have their radio-to-optical vector along the jet, with the optical centroid downstream from the radio centroids, and that the K and Ka centroids are preferably upstream in the jet with respect to the X centroid, which is consistent with the paradigm of a simple core–jet model. For a population of multiwavelength positions aligned along the jet, astrometric information can therefore be used to measure the direction of the jet independently of imaging. In addition, we find several sources for which the optical centroid coincides with stationary radio features with a relatively high fraction of polarization, indicating optical emission dominated by a synchrotron process in the jet.

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Section: Analysis and Resultsmentioning

confidence: 54%

Parsec-scale alignments of radio-optical offsets with jets in AGNs from multifrequency geodetic VLBI, Gaia EDR3, and the MOJAVE program

Lambert

Liu

Arias

et al. 2021

A&A

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“…VLBI-Gaia offsets are a widely discussed topic (e.g. Kovalev, Petrov & Plavin 2017;Xu et al 2021, and references therein) and it has been shown that such offsets can be used as a tool to distinguish between the accretion disc and jet emission regions (Plavin, Kovalev & Petrov 2019). Six sources from our sample have coordinates within 0.5 arcsec from optical sources in the Gaia EDR 3 (Gaia Collaboration 2021).…”

Section: Smile L9mentioning

confidence: 99%

SMILE: Search for MIlli-LEnses

Casadio

Blinov

Readhead

et al. 2021

Monthly Notices of the Royal Astronomical Society: Letters

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Dark Matter (DM) halos with masses below ∼108M⊙, which would help to discriminate between DM models, may be detected through their gravitational effect on distant sources. The same applies to primordial black holes, considered as an alternative scenario to DM particle models. However, there is still no evidence for the existence of such objects. With the aim of finding compact objects in the mass range ∼ 106 – 109M⊙, we search for strong gravitational lenses on milli (mas)-arcseconds scales (< 150 mas). For our search, we used the Astrogeo VLBI FITS image database – the largest publicly available database, containing multi-frequency VLBI data of 13828 individual sources. We used the citizen science approach to visually inspect all sources in all available frequencies in search for images with multiple compact components on mas-scales. At the final stage, sources were excluded based on the surface brightness preservation criterion. We obtained a sample of 40 sources that passed all steps and therefore are judged to be milli-arcsecond lens candidates. These sources are currently followed-up with on-going European VLBI Network (EVN) observations at 5 and 22 GHz. Based on spectral index measurements, we suggest that two of our candidates have a higher probability to be associated with gravitational lenses.

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“…However, we found a lack of connection (correlation coefficient smaller than +0.1 with a p-value of about 0.4). Since the CARMS was supposed to be correlated with the structure index (Xu et al 2019) and Xu et al (2021) reported the existence of a connection between the Gaia-VLBI and the CARMS, it is surprising that the correlation tests lead to different results. We have no explanation yet in this regard and leave it for a future investigation.…”

Section: Cause Of Optical-to-radio Distancementioning

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

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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.

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Evidence of theGaia–VLBI position differences being related to radio source structure

Cited by 20 publications

References 39 publications

Parsec-scale alignments of radio-optical offsets with jets in AGNs from multifrequency geodetic VLBI, Gaia EDR3, and the MOJAVE program

Parsec-scale alignments of radio-optical offsets with jets in AGNs from multifrequency geodetic VLBI, Gaia EDR3, and the MOJAVE program

SMILE: Search for MIlli-LEnses

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

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