The VLBA CANDELS GOODS-North Survey. I – Survey Design, Processing, Data Products, and Source Counts
arxiv(2024)
摘要
The past decade has seen significant advances in wide-field cm-wave very long
baseline interferometry (VLBI), which is timely given the wide-area, synoptic
survey-driven strategy of major facilities across the electromagnetic spectrum.
While wide-field VLBI poses significant post-processing challenges that can
severely curtail its potential scientific yield, many developments in the
km-scale connected-element interferometer sphere are directly applicable to
addressing these. Here we present the design, processing, data products, and
source counts from a deep (11 μJy beam^-1), quasi-uniform sensitivity,
contiguous wide-field (160 arcmin^2) 1.6 GHz VLBI survey of the CANDELS
GOODS-North field. This is one of the best-studied extragalactic fields at
milli-arcsecond resolution and, therefore, is well-suited as a comparative
study for our Tera-pixel VLBI image. The derived VLBI source counts show
consistency with those measured in the COSMOS field, which broadly traces the
AGN population detected in arcsecond-scale radio surveys. However, there is a
distinctive flattening in the S_ 1.4GHz∼100-500 μJy flux density
range, which suggests a transition in the population of compact faint radio
sources, qualitatively consistent with the excess source counts at 15 GHz that
is argued to be an unmodelled population of radio cores. This survey approach
will assist in deriving robust VLBI source counts and broadening the discovery
space for future wide-field VLBI surveys, including VLBI with the Square
Kilometre Array, which will include new large field-of-view antennas on the
African continent at ≳1000 km baselines. In addition, it may be useful
in the design of both monitoring and/or rapidly triggered VLBI transient
programmes.
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