The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging

Tasse, C.; Shimwell, T.; Hardcastle, M.J.; O'Sullivan, S.P.; van Weeren, R.; Best, P.N.; Bester, L.; Hugo, B.; Smirnov, O.; Sabater, J.; Calistro-Rivera, G.; de Gasperin, F.; Morabito, L.K.; Röttgering, H.; Williams, W.L.; Bonato, M.; Bondi, M.; Botteon, A.; Brüggen, M.; Brunetti, G.; Chyży, K.T.; Garrett, M.A.; Gürkan, G.; Jarvis, M.J.; Kondapally, R.; Mandal, S.; Prandoni, I.; Repetti, A.; Retana-Montenegro, E.; Schwarz, D.J.; Shulevski, A.; Wiaux, Y.

Abstract

The Low Frequency Array (LOFAR) is an ideal instrument to conduct deep extragalactic surveys. It has a large field of view and is sensitive to large-scale and compact emission. It is, however, very challenging to synthesize thermal noise limited maps at full resolution, mainly because of the complexity of the low-frequency sky and the direction dependent effects (phased array beams and ionosphere). In this first paper of a series, we present a new calibration and imaging pipeline that aims at producing high fidelity, high dynamic range images with LOFAR High Band Antenna data, while being computationally efficient and robust against the absorption of unmodeled radio emission. We apply this calibration and imaging strategy to synthesize deep images of the Boötes and Lockman Hole fields at ∼150 MHz, totaling ∼80 and ∼100 h of integration, respectively, and reaching unprecedented noise levels at these low frequencies of .30 and .23 µJy beam−1 in the inner ∼3 deg2 . This approach is also being used to reduce the LOTSS-wide data for the second data release.

Citation

Tasse, C., Shimwell, T., Hardcastle, M., O'Sullivan, S., van Weeren, R., Best, P., Bester, L., Hugo, B., Smirnov, O., Sabater, J., Calistro-Rivera, G., de Gasperin, F., Morabito, L., Röttgering, H., Williams, W., Bonato, M., Bondi, M., Botteon, A., Brüggen, M., Brunetti, G., …Wiaux, Y. (2021). The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging. Astronomy & Astrophysics, 648, Article A1. https://doi.org/10.1051/0004-6361/202038804

• Journal Article Type: Article
• Acceptance Date: Nov 14, 2020
• Online Publication Date: Apr 7, 2021
• Publication Date: 2021-04
• Deposit Date: Jan 11, 2021
• Publicly Available Date: Apr 19, 2021
• Journal: Astronomy and astrophysics.
• Print ISSN: 0004-6361
• Electronic ISSN: 1432-0746
• Publisher: EDP Sciences
• Peer Reviewed: Peer Reviewed
• Volume: 648
• Article Number: A1
• DOI: https://doi.org/10.1051/0004-6361/202038804
• Public URL: https://durham-repository.worktribe.com/output/1253595