A New Version of the OCARS Catalog of Optical Characteristics of Astrometric Radio Sources

Malkin, Zinovy

doi:10.3847/1538-4365/aae777

Cited by 32 publications

(15 citation statements)

References 77 publications

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“…For the sources that have been imaged, indicators about their astrometric suitability (i.e., source structure indices and compactness) are available from the BVID database. As supplemental information, the basic optical characteristics of most ICRF3 sources may be found in the Optical Characteristics of Astrometric Radio Sources catalog (Malkin 2018). The ICRF3 source coordinates reported in Tables 10-12 are provided for epoch 2015.0.…”

Section: Practical Use Of the Framementioning

confidence: 99%

The third realization of the International Celestial Reference Frame by very long baseline interferometry

Charlot

Jacobs

Gordon

et al. 2020

A&A

Self Cite

247

241

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A new realization of the International Celestial Reference Frame (ICRF) is presented based on the work achieved by a working group of the International Astronomical Union (IAU) mandated for this purpose. This new realization follows the initial realization of the ICRF completed in 1997 and its successor, ICRF2, adopted as a replacement in 2009. The new frame, referred to as ICRF3, is based on nearly 40 years of data acquired by very long baseline interferometry at the standard geodetic and astrometric radio frequencies (8.4 and 2.3 GHz), supplemented with data collected at higher radio frequencies (24 GHz and dual-frequency 32 and 8.4 GHz) over the past 15 years. State-of-the-art astronomical and geophysical modeling has been used to analyze these data and derive source positions. The modeling integrates, for the first time, the effect of the galactocentric acceleration of the solar system (directly estimated from the data) which, if not considered, induces significant deformation of the frame due to the data span. The new frame includes positions at 8.4 GHz for 4536 extragalactic sources. Of these, 303 sources, uniformly distributed on the sky, are identified as “defining sources” and as such serve to define the axes of the frame. Positions at 8.4 GHz are supplemented with positions at 24 GHz for 824 sources and at 32 GHz for 678 sources. In all, ICRF3 comprises 4588 sources, with three-frequency positions available for 600 of these. Source positions have been determined independently at each of the frequencies in order to preserve the underlying astrophysical content behind such positions. They are reported for epoch 2015.0 and must be propagated for observations at other epochs for the most accurate needs, accounting for the acceleration toward the Galactic center, which results in a dipolar proper motion field of amplitude 0.0058 milliarcsecond yr−1 (mas yr−1). The frame is aligned onto the International Celestial Reference System to within the accuracy of ICRF2 and shows a median positional uncertainty of about 0.1 mas in right ascension and 0.2 mas in declination, with a noise floor of 0.03 mas in the individual source coordinates. A subset of 500 sources is found to have extremely accurate positions, in the range of 0.03–0.06 mas, at the traditional 8.4 GHz frequency. Comparing ICRF3 with the recently released Gaia Celestial Reference Frame 2 in the optical domain, there is no evidence for deformations larger than 0.03 mas between the two frames, in agreement with the ICRF3 noise level. Significant positional offsets between the three ICRF3 frequencies are detected for about 5% of the sources. Moreover, a notable fraction (22%) of the sources shows optical and radio positions that are significantly offset. There are indications that these positional offsets may be the manifestation of extended source structures. This third realization of the ICRF was adopted by the IAU at its 30th General Assembly in August 2018 and replaced the previous realization, ICRF2, on January 1, 2019.

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Section: Practical Use Of the Framementioning

confidence: 99%

The third realization of the International Celestial Reference Frame by very long baseline interferometry

Charlot

Jacobs

Gordon

et al. 2020

A&A

Self Cite

247

241

View full text Add to dashboard Cite

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“…(iii) The Optical Characteristics of Astrometric Radio Sources (OCARS) catalogue of Very Long Baseline Interferometry (VLBI) astrometry sources (Ma et al 2009;Malkin 2018). Of the 3663 sources, 2404 are classified as quasars, but given that these are very strong radio calibration sources we assume that all of the nongalaxies are active galactic nuclei (AGN), giving a sample size of 3033.…”

Section: The Datamentioning

confidence: 99%

Quasar photometric redshifts from incomplete data using Deep Learning

Curran

2022

Preprint

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Forthcoming astronomical surveys are expected to detect new sources in such large numbers that measuring their spectroscopic redshift measurements will be not be practical. Thus, there is much interest in using machine learning to yield the redshift from the photometry of each object. We are particularly interested in radio sources (quasars) detected with the Square Kilometre Array and have found Deep Learning, trained upon a large optically-selected sample of quasi-stellar objects, to be effective in the prediction of the redshifts in three external samples of radio-selected sources. However, the requirement of nine different magnitudes, from the near-infrared, optical and ultra-violet bands, has the effect of significantly reducing the number of sources for which redshifts can be predicted. Here we explore the possibility of using machine learning to impute the missing features. We find that for the training sample, simple imputation is sufficient, particularly replacing the missing magnitude with the maximum for that band, thus presuming that the non-detection is at the sensitivity limit. For the test samples, however, this does not perform as well as multivariate imputation, which suggests that many of the missing magnitudes are not limits, but have indeed not been observed. From extensive testing of the models, we suggest that the imputation is best restricted to two missing values per source. Where the sources overlap on the sky, in the worst case, this increases the fraction of sources for which redshifts can be estimated from 46% to 80%, with > 90% being reached for the other samples.

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“…The database contained 15235 sources and a total of 103483 images at various frequency bands. Redshift information used in this work was retrieved from the OCARS catalog (Malkin 2018).…”

Section: Data Sample and Reductionmentioning

confidence: 99%

Local alignments of parsec-scale AGN radiojets

Mandarakas,

Blinov,

Casadio

et al. 2021

Preprint

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Context. Coherence in the characteristics of neighboring sources in 2D and 3D space may suggest the existence of large-scale cosmic structures, which are useful for cosmological studies. Numerous works have been conducted to detect such features in global scales as well as in confined areas of the sky. However, results are often contradictory and their interpretation remains controversial.Aims. We investigate the potential alignment of parsec-scale radio jets in localized regions of the coordinates-redshift space. Methods. We use data from the Astrogeo VLBI FITS image database to deduce jet directions of radio sources. We perform the search for statistical alignments between nearby sources and explore the impact of instrumental biases. Results. We unveil four regions for which the alignment between jet directions deviates from randomness at a significance level of more than 5 σ and is unlikely due to instrumental systematics. Intriguingly, their locations coincide with other known large-scale cosmic structures and/or regions of alignments. Conclusions. If the alignments found are the result of physical processes, the discovered regions may designate some of the largest structures known to date.

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A New Version of the OCARS Catalog of Optical Characteristics of Astrometric Radio Sources

Cited by 32 publications

References 77 publications

The third realization of the International Celestial Reference Frame by very long baseline interferometry

The third realization of the International Celestial Reference Frame by very long baseline interferometry

Quasar photometric redshifts from incomplete data using Deep Learning

Local alignments of parsec-scale AGN radiojets

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