Parsec-scale properties of steep and flat spectrum extragalactic radio sources from a VLBA survey of a complete north polar cap sample

Abstract

We observed with the VLBA at 2.3 and 8.6 GHz a complete flux-density limited sample of 482 radio sources with declination >+75 degrees brighter than 200 mJy at 1.4 GHz drawn from the NVSS catalog. 34% of the sources show parsec-scale emission above the flux density detection limit of 30 mJy; their accurate positions and parsec-scale structure parameters are determined. Among all the sources detected at least at the shortest VLBA baselines, the majority, or 72%, has a steep single-dish spectrum. The fraction of the sources with a detectable parsec-scale structure is above 95% among the flat-spectrum and close to 25% among the steep-spectrum objects. We identified 82 compact steep-spectrum source candidates, which make up 17% of the sample; most of them are reported for the first time. The compactness and the brightness temperature of the sources in our sample show a positive correlation with single-dish and VLBA spectral indices. All the sources with a significant 8 GHz variability were detected by the VLBA snapshot observations, which independently confirmed their compactness. We demonstrated that 54% of the sources detected by the VLBA at 2.3 GHz in our sample have a steep VLBA spectrum. The compact radio emission of these sources is likely dominated by optically thin jets or mini-lobes, not by an opaque jet core. These results show that future VLBI surveys aimed to search for new sources with parsec-scale structure should include not only flat-spectrum sources, but also steep-spectrum ones in order to reach an acceptable level of completeness.

arXiv comment27 pages, 16 figures (of them, 4 are figure sets), 7 tables (of them, 5 are machine readable); accepted to The Astronomical Journal. The machine readable tables and complete figure sets can be downloaded as ancillary files

References in corpus (43)

• Astropy: A Community Python Package for Astronomy
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• On the Estimation of Confidence Intervals for Binomial Population Proportions in Astronomy: The Simplicity and Superiority of the Bayesian Approach
• Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine Scale Structure
• The Australia Telescope 20 GHz Survey: The Source Catalogue
• The VLBA Calibrator Survey - VCS1
• The VLBA Imaging and Polarimetry Survey at 5 GHz
• The faint radio sky: radio astronomy becomes mainstream
• A test for partial correlation with censored astronomical data
• The Third VLBA Calibrator Survey
• The Sixth VLBA Calibrator Survey: VCS6
• The Fifth VLBA Calibrator Survey: VCS5
• Observational evidence for the origin of high-energy neutrinos in parsec-scale nuclei of radio-bright active galaxies
• Radio Loud and Radio Quiet Quasars
• The Fourth VLBA Calibrator Survey - VCS4
• MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. XI. Spectral distributions
• Single-epoch VLBI imaging study of bright active galactic nuclei at 2 and 8 GHz
• AGN and Starburst Radio Emission from Optically Selected QSOs
• Survey of Instantaneous 1-22 GHz Spectra of 550 Compact Extragalactic Objects with Declinations from -30deg to +43deg
• The VLBA Galactic Plane Survey -- VGaPS
• A quantitative analysis of systematic differences in positions and proper motions of Gaia DR2 with respect to VLBI
• Milky Way scattering properties and intrinsic sizes of active galactic nuclei cores probed by very long baseline interferometry surveys of compact extragalactic radio sources
• The Bologna Complete Sample of Nearby Radio Sources
• mJIVE-20: a survey for compact mJy radio objects with the Very Long Baseline Array
• The wide-field VLBA calibrator survey -- WFCS
• The LBA Calibrator Survey of southern compact extragalactic radio sources - LCS1
• The faint radio sky: VLBA observations of the COSMOS field
• FIRST-based survey of Compact Steep Spectrum sources, IV. Multifrequency VLBA observations of very compact objects
• A sample of small size compact steep-spectrum radio sources. VLBI images and VLA polarization at 5 GHz
• Detection statistics of the RadioAstron AGN survey
• The Bologna complete sample of nearby radio sources: II -- phase referenced observations of faint nuclear sources
• Spurious source generation in mapping from noisy phase-self-calibrated data
• The AT20G high angular resolution catalogue
• Nowhere to Hide: Radio-faint AGN in the GOODS-N field. I. Initial catalogue and radio properties
• The Second LBA Calibrator Survey of southern compact extragalactic radio sources - LCS2
• On the coherence loss in phase-referenced VLBI observations
• FIRST-based survey of Compact Steep Spectrum sources, V. Milliarcsecond-scale morphology of CSS objects
• VLBI ecliptic plane survey: VEPS-1
• On the dust geometry in radio-loud active galactic nuclei
• Observations of the bright radio sources in the North Celestial Pole region at the RATAN-600 radio telescope
• High-resolution Observations of Low-luminosity Gigahertz-Peaked Spectrum and Compact Steep Spectrum Sources
• FIRST-based survey of Compact Steep Spectrum sources, III. MERLIN and VLBI observations of subarcsecond-scale objects
• A 20 GHz Bright Sample for Delta > 72 deg - II. Multi-frequency Follow-up

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