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- Deane, R. P., et al.
(författare)
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The VLBA CANDELS GOODS-North Survey -I. survey design, processing, data products, and source counts
- 2024
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 529:3, s. 2428-2442
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Tidskriftsartikel (refereegranskat)abstract
- 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, man y dev elopments 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 surv e y 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 surv e ys. Ho we ver, 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 surv e y approach will assist in deriving robust VLBI source counts and broadening the disco v ery space for future wide-field VLBI surv e ys, 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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| 2. |
- Wandia, Kelvin, et al.
(författare)
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An interferometric SETI observation of Kepler-111 b
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 522:3, s. 3784-3794
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Tidskriftsartikel (refereegranskat)abstract
- The application of very long baseline interferometry (VLBI) to the search for extraterrestrial intelligence (SETI) has been limited to date, despite the technique offering many advantages over traditional single-dish SETI observations. In order to further develop interferometry for SETI, we used the European VLBI network (EVN) at 21 cm to observe potential secondary phase calibrators in the Kepler field. Unfortunately, no secondary calibrators were detected. However, a VLBA primary calibrator in the field, J1926+4441, offset only ∼1.88 arcmin from a nearby exoplanet Kepler-111 b, was correlated with high temporal (0.25 s) and spectral (16384 × 488 Hz channels) resolution. During the analysis of the high-resolution data, we identified a spectral feature that was present in both the auto and cross-correlation data with a central frequency of 1420.424 ± 0.0002 MHz and a width of 0.25 MHz. We demonstrate that the feature in the cross-correlations is an artefact in the data, associated with a significant increase in each telescope's noise figure due to the presence of H I in the beam. This would typically go unnoticed in data correlated with standard spectral resolution. We flag (excluded from the subsequent analysis) these channels and phase rotate the data to the location of Kepler-111 b aided by the Gaia catalogue and search for signals with SNR > 7. At the time of our observations, we detect no transmitters with an equivalent isotropically radiated power ≳4 × 1015 W.
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