English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present an analysis of the detection fraction and the number counts ofradio sources imaged with Very Long Baseline Interferometry (VLBI) at 1.4 GHzas part of the mJIVE-20 survey. From a sample of 24,903 radio sourcesidentified by FIRST, 4,965 are detected on VLBI-scales, giving an overalldetection fraction of $19.9\pm2.9~$per cent. However, we find that thedetection fraction falls from around 50 per cent at a peak surface brightnessof $80~mJy~beam^{-1}$ in FIRST to around 8 per cent at the detection limit,which is likely dominated by the surface brightness sensitivity of the VLBIobservations, with some contribution from a change in the radio sourcepopulation. We also find that compactness at arcsec-scales is the dominantfactor in determining whether a radio source is detected with VLBI, and thatthe median size of the VLBI-detected radio sources is 7.7 mas. After correctingfor the survey completeness and effective sky area, we determine the slope ofthe differential number counts of VLBI-detected radio sources with fluxdensities $S_{\rm 1.4~GHz} > 1~mJy$ to be $\eta_{\rm VLBI} = -1.74\pm 0.02$,which is shallower than in the cases of the FIRST parent population ($\eta_{\rmFIRST} = -1.77\pm 0.02$) and for compact radio sources selected at higherfrequencies ($\eta_{\rm JBF} = -2.06\pm 0.02$). From this, we find that all-sky($3\pi~sr$) surveys with the EVN and the VLBA have the potential to detect$(7.2\pm0.9)\times10^{5}$ radio sources at mas-resolution, and that the densityof compact radio sources is sufficient (5.3~deg$^{-2}$) for in-beam phasereferencing with multiple sources (3.9 per primary beam) in the case of ahypothetical SKA-VLBI array.

On the source counts of VLBI-detected radio sources and the prospects of all-sky surveys with current and next generation instruments