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

Abstract

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. 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. 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. 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.

9 pages, 6 figures, 2 tables, accepted for publication in A&A

References in corpus (10)

• The Gaia mission
• The third realization of the International Celestial Reference Frame by very long baseline interferometry
• Opacity in compact extragalactic radio sources and its effect on astrophysical and astrometric studies
• VLBI-Gaia offsets favor parsec-scale jet direction in Active Galactic Nuclei
• Gaia Data Release 1: The reference frame and the optical properties of ICRF sources
• On significance of VLBI/Gaia position offsets
• Astrometric evidence for a population of dislodged AGN
• Astrometric suitability of optically-bright ICRF sources for the alignment with the future Gaia celestial reference frame
• Evidence of the $Gaia$--VLBI position differences being related to radio source structure
• Systematics and accuracy of VLBI astrometry: What can be learned from a comparison with Gaia Data Release 2

Cited by in corpus (5)

• Quasars with Proper Motions and the Link to Double and Multiple AGNs
• Impacts of the image alignment over frequency for VLBI Global Observing System
• Time-lapse Very Long Baseline Interferometry Imaging of the Close Active Binary HR 1099
• The Quasar CTD 135 is Not a Compact Symmetric Object
• Astrometric properties of reference frame sources as a function of redshift