A Point-source Catalogue from Direction-dependent Calibrated 21CMA Images
- 1State Key Laboratory of Radio Astronomy and Technology , Shanghai Astronomical Observatory, CAS, 80 Nandan Road, Shanghai 200030 ,
- 2School of Astronomy and Space Science, University of Chinese Academy of Sciences , Beijing 100049 ,
- 3State Key Laboratory of Radio Astronomy and Technology, National Astronomical Observatories , CAS, 20A Datun Road, Beijing 100101 ,
Abstract
We present a deep low-frequency radio point-source catalogue centred on the North Celestial Pole (NCP) and extending 5○ in radius, derived from a single 24-h observation with the 21 CentiMeter Array (21CMA). Covering 75–175 MHz, the catalogue characterises extragalactic foreground point sources for Epoch of Reionization (EoR) studies. Previous 21CMA imaging has been limited by reduced dynamic range caused by direction-dependent effects, particularly the severe grating lobes of ultra-bright sources such as 3C 61.1 and ionospheric phase distortions. Here we apply 21CMAcali, a direction-dependent calibration and imaging pipeline, to mitigate these effects. The angular resolution ranges from 2.3 arcmin at 100 MHz to 1.4 arcmin at 168.75 MHz. The resulting maps show reduced artefacts and background noise, enabling more reliable recovery of faint sources. We construct a catalogue of 1246 radio point sources. Cross-matching with LoTSS-DR3, WENSS, and NVSS enables broad-band spectral fitting, while an independent in-band analysis yields a median spectral index of α = −0.825 (where S∝να). The Euclidean-normalised differential source counts at 150 MHz, derived from a dedicated 50-MHz-wide multi-frequency synthesis (MFS) image, are broadly consistent with existing measurements and semi-empirical models at the bright end, whereas the deficit at lower flux densities (S ≲ 0.04 Jy) mainly reflects limited sensitivity and incompleteness. This catalogue improves foreground point-source characterisation in the 21CMA NCP field, demonstrates the value of direction-dependent calibration, and provides a reference for deeper catalogues based on multi-day observations.
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BibTeX
@article{tang2026pointsource,
title = {{A Point-source Catalogue from Direction-dependent Calibrated 21CMA Images}},
author = {Qizhe Tang and Jingying Wang and Junhua Gu and Qian Zheng and Quan Guo and Tingyan Shen and Bixuan Zhao and Qiuyi Lai and Yan Huang and Kuanjun Li and Yang Feng},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag2080},
url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2080/9005967},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - A Point-source Catalogue from Direction-dependent Calibrated 21CMA Images
AU - Qizhe Tang
AU - Jingying Wang
AU - Junhua Gu
AU - Qian Zheng
AU - Quan Guo
AU - Tingyan Shen
AU - Bixuan Zhao
AU - Qiuyi Lai
AU - Yan Huang
AU - Kuanjun Li
AU - Yang Feng
PY - 2026
DA - 2026/10/31
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag2080
UR - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2080/9005967
AB - We present a deep low-frequency radio point-source catalogue centred on the North Celestial Pole (NCP) and extending 5○ in radius, derived from a single 24-h observation with the 21 CentiMeter Array (21CMA). Covering 75–175 MHz, the catalogue characterises extragalactic foreground point sources for Epoch of Reionization (EoR) studies. Previous 21CMA imaging has been limited by reduced dynamic range caused by direction-dependent effects, particularly the severe grating lobes of ultra-bright sources such as 3C 61.1 and ionospheric phase distortions. Here we apply 21CMAcali, a direction-dependent calibration and imaging pipeline, to mitigate these effects. The angular resolution ranges from 2.3 arcmin at 100 MHz to 1.4 arcmin at 168.75 MHz. The resulting maps show reduced artefacts and background noise, enabling more reliable recovery of faint sources. We construct a catalogue of 1246 radio point sources. Cross-matching with LoTSS-DR3, WENSS, and NVSS enables broad-band spectral fitting, while an independent in-band analysis yields a median spectral index of α = −0.825 (where S∝να). The Euclidean-normalised differential source counts at 150 MHz, derived from a dedicated 50-MHz-wide multi-frequency synthesis (MFS) image, are broadly consistent with existing measurements and semi-empirical models at the bright end, whereas the deficit at lower flux densities (S ≲ 0.04 Jy) mainly reflects limited sensitivity and incompleteness. This catalogue improves foreground point-source characterisation in the 21CMA NCP field, demonstrates the value of direction-dependent calibration, and provides a reference for deeper catalogues based on multi-day observations.
SN - 0035-8711
SN - 1365-2966
ER -