- ID:
- ivo://CDS.VizieR/J/A+A/425/99
- Title:
- VLBI and VLA obs. of Seyfert galaxies
- Short Name:
- J/A+A/425/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained mas-scale resolution very long baseline interferometry (VLBI) images of a sample of Seyfert 1 and Seyfert 2 galaxies at 5GHz (wavelength, {lambda}=6cm). The Seyferts of the two types were chosen to be matched in several orientation-independent properties, primarily in order to rigorously test predictions of the unified scheme. We detected all the 15 objects that we observed. In this paper we describe the observations and data reduction procedures, and present the VLBI radio images as well as simultaneous Very Large Array images that we obtained for these 15 Seyferts.
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- ID:
- ivo://CDS.VizieR/J/A+A/520/A113
- Title:
- VLBI detection of 398 extragalactic radio sources
- Short Name:
- J/A+A/520/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The European space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames with the highest possible accuracy. It has been found that only 70 (10%) of the sources from the International Celestial Reference Frame (ICRF) are suitable for establishing this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of 447 optically- bright (magnitude <=18) extragalactic radio sources, typically 20 times weaker than the ICRF sources, which have been selected by cross-correlating an optical quasar catalog with the NRAO VLA Sky Survey (NVSS, Cat. VIII/65). This paper presents the observing strategy to detect, image, and measure accurate radio positions for these sources. It also provides results on the VLBI detectability of the sources, as derived from initial observations with the European VLBI Network in June and October 2007. Based on these observations, a high detection rate of 89% is found, which is promising for the continuation of this project. This high VLBI detection rate for sources from the NVSS catalog is probably due to the selection process, suggesting that optically-bright quasars have compact radio structures.
- ID:
- ivo://CDS.VizieR/J/ApJS/230/13
- Title:
- VLBI Ecliptic Plane Survey: VEPS-1
- Short Name:
- J/ApJS/230/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here the results of the first part of the VLBI Ecliptic Plane Survey (VEPS) program. The goal of the program is to find all compact sources within 7.5{deg} of the ecliptic plane that are suitable as calibrators for anticipated phase referencing observations of spacecraft, and determine their positions with accuracy at the 1.5 nrad level. We run the program in two modes: search and refine. In the search mode, a complete sample of all sources brighter than 50mJy at 5GHz listed in the Parkes-MIT-NRAO and Green Bank 6cm (GB6) catalogs, except those previously detected with VLBI, is observed. In the refining mode, the positions of all ecliptic plane sources, including those found in the search mode, are improved. By 2016 October, thirteen 24hr sessions that targeted all sources brighter than 100mJy have been observed and analyzed. Among 3320 observed target sources, 555 objects have been detected. We also conducted a number of follow-up VLBI experiments in the refining mode and improved the positions of 249 ecliptic plane sources.
- ID:
- ivo://CDS.VizieR/J/A+A/526/A102
- Title:
- VLBI imaging of 105 extragalactic radio sources
- Short Name:
- J/A+A/526/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The European space astrometry mission Gaia, to be launched by 2012, will construct a dense optical QSO-based celestial reference frame which will need to be linked to the International Celestial Reference Frame (ICRF; the IAU fundamental frame), with the highest accuracy. However, it has been found that only 10% of the ICRF sources (70 sources) are suitable to establish this link. The remaining sources are not useful either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the accuracy of this alignment, we have developed a program of VLBI observations based on three steps to detect, image and measure astrometric positions of weak extragalactic radio sources, with bright optical counterparts, from a sample of 447 candidate sources. The experiments devoted to VLBI detection, carried out with the European VLBI Network (EVN) in June and October 2007, were very successful, with 398 sources detected at both S- and X-bands. From these, 105 sources were observed in March 2008 with a global VLBI array (EVN and VLBA; Very Long Baseline Array) for imaging their VLBI structures. All sources were successfully imaged in both bands and about 50% (47 sources) were found to be point-like on VLBI scales. These images are available at http://www.obs.u-bordeaux1.fr/BVID/GC030/. VLBI positions of these sources will be measured accurately in future astrometric experiments.
- ID:
- ivo://CDS.VizieR/J/A+A/466/63
- Title:
- VLBI observations of BL Lac objects
- Short Name:
- J/A+A/466/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present EVN observations of seven BL Lac objects selected from the RGB sample. To investigate the intrinsic radiation property of BL Lac objects, we estimated the Doppler factor with the VLA or MERLIN core and the total 408MHz luminosity for a sample of 170 BL Lac objects. The intrinsic (comoving) synchrotron peak frequency was then calculated by using the estimated Doppler factor. Assuming a Lorentz factor of 5, the viewing angle of jets was constrained. The high-resolution VLBI images of seven sources all show a core-jet structure. We estimated the proper motions of three sources with the VLBI archive data, and find that the apparent speed increases with the distance of components to the core for all of them.
- ID:
- ivo://CDS.VizieR/J/AJ/127/3609
- Title:
- VLBI observations of southern ICRF sources
- Short Name:
- J/AJ/127/3609
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 8.4GHz very long baseline interferometry (VLBI) observations of 69 southern hemisphere extragalactic sources in the International Celestial Reference Frame. These are the first in a series of observations intended to image all such sources at milliarcsecond resolution in order to determine their continued suitability for reference-frame use based on intrinsic structure. We use the resultant images to calculate a core fraction, that is, the ratio of core flux density to total flux density, for all observed sources. The resulting distribution, with a mean value of 0.83, suggests that most sources are relatively compact. However, just over half the observed sources show significant extended emission in the form of multiple compact components. These sources are probably poorly suited for high-accuracy reference-frame use unless intrinsic structure and potential variability can be taken into account. Our observations represent the first large, comprehensive VLBI imaging survey in the southern hemisphere, significantly extending the existing limited VLBI surveys and, along with some well-known objects, containing many sources that have never been imaged at milliarcsecond resolution. The overlap with Very Long Baseline Array images of sources between 0{deg} and -35{deg} declination helps determine the limits to imaging with the southern hemisphere-accessible telescopes.
- ID:
- ivo://CDS.VizieR/J/ApJ/589/733
- Title:
- VLBI polarimetry of CJF sources
- Short Name:
- J/ApJ/589/733
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Very Long Baseline Array observations and a statistical analysis of 5GHz VLBI polarimetry data from 177 sources in the Caltech-Jodrell Bank Flat-Spectrum (CJF) survey. The CJF survey, a complete, flux density-limited sample of 293 extragalactic radio sources, gives us the unique opportunity to compare a broad range of source properties for quasars, galaxies, and BL Lacertae objects. We focus primarily on jet properties, specifically, the correlation between the jet axis angle and the polarization angle in the core and jet. A strong correlation is found for the electric vector polarization angle in the cores of quasars to be perpendicular to the jet axis. Contrary to previous claims, no correlation is found between the jet polarization angle and the jet axis in either quasars or BL Lac objects. With this large, homogeneous sample we are also able to investigate cosmological issues and active galactic nucleus evolution.
- ID:
- ivo://CDS.VizieR/J/AZh/81/1032
- Title:
- VLBI Position Measurements
- Short Name:
- J/AZh/81/1032
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A large number (~2 million) of VLBI observations have been reduced in order to re ne the measured coordinates of the observed radio sources. The data reduction was carried out in the OCCAM package using the least squares colocation method. Corrections to the coordinates of 642 objects were derived. The accuracy of the catalog is no worse than 0.2 milliseconds of arc for stable sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/673/78
- Title:
- VLBI suvey around B0218+357 at 90cm
- Short Name:
- J/ApJ/673/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the first wide-field, very long baseline interferometry (VLBI) survey at 90cm. The survey area consists of two overlapping 28deg^2^ fields centered on the quasar J0226+3421 and the gravitational lens B0218+357. A total of 618 sources were targeted in these fields, based on identifications from Westerbork Northern Sky Survey (WENSS) data. Of these sources, 272 had flux densities that, if unresolved, would fall above the sensitivity limit of the VLBI observations. A total of 27 sources were detected as far as 2{deg} from the phase center. The results of the survey suggest that at least 10% of moderately faint (S~100mJy) sources found at 90 cm contain compact components smaller than ~0.1"-0.3" and stronger than 10% of their total flux densities.
- ID:
- ivo://CDS.VizieR/J/ApJS/155/33
- Title:
- VSOP 5 GHz AGN Survey. III
- Short Name:
- J/ApJS/155/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The VLBI Space Observatory Programme (VSOP) mission is a Japanese-led project to study radio sources with sub-milliarcsec resolution using an orbiting 8m telescope, HALCA, along with global arrays of Earth-based telescopes. Approximately 25% of the observing time is devoted to a survey of compact active galactic nuclei (AGNs) that are stronger than 1Jy at 5GHz - the VSOP AGN Survey. This paper, the third in the series, presents the results from the analysis of the first 102 Survey sources.
