Application of Regularization Methods in the Sky Map Reconstruction of the Tianlai Cylinder Pathfinder Array

• Published in: Research in astronomy and astrophysics Vol. 24; no. 2; pp. 25002 - 35
• Main Authors: Yu, Kaifeng, Zuo, Shifan, Wu, Fengquan, Wang, Yougang, Chen, Xuelei
• Format: Journal Article
• Language: English
• Published: Beijing National Astromonical Observatories, CAS and IOP Publishing 01.02.2024; IOP Publishing; Center of High Energy Physics,Peking University,Beijing 100871,China; School of Astronomy and Space Science,University of Chinese Academy of Sciences,Beijing 100049,China%National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100101,China; School of Astronomy and Space Science,University of Chinese Academy of Sciences,Beijing 100049,China; National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100101,China; Key Laboratory of Radio Astronomy and Technology,Chinese Academy of Sciences,Beijing 100101,China; Key Laboratory of Radio Astronomy and Technology,Chinese Academy of Sciences,Beijing 100101,China%National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100101,China; Key Laboratory of Cosmology and Astrophysics(Liaoning)& College of Sciences,Northeastern University,Shenyang 110819,China
• Subjects: Arrays; Astronomical maps; cosmology: observations; Cylinders; Drift; Field of view; Interferometers; Inverse problems; Ionization; methods: numerical; Northern Hemisphere; Parameters; radio continuum: general; Radio interferometers; Regularization; Regularization methods; Singular value decomposition; Sky surveys (astronomy); techniques: interferometric; methods:numerical; techniques:interferometric; cosmology:observations; radio continuum:general
• ISSN: 1674-4527; 2397-6209
• DOI: 10.1088/1674-4527/ad1223

The Tianlai cylinder pathfinder is a radio interferometer array to test 21 cm intensity mapping techniques in the post-reionization era. It works in passive drift scan mode to survey the sky visible in the northern hemisphere. To deal with the large instantaneous field of view and the spherical sky, we decompose the drift scan data into m -modes, which are linearly related to the sky intensity. The sky map is reconstructed by solving the linear interferometer equations. Due to incomplete uv coverage of the interferometer baselines, this inverse problem is usually ill-posed, and regularization method is needed for its solution. In this paper, we use simulation to investigate two frequently used regularization methods, the Truncated Singular Value Decomposition (TSVD), and the Tikhonov regularization techniques. Choosing the regularization parameter is very important for its application. We employ the generalized cross validation method and the L-curve method to determine the optimal value. We compare the resulting maps obtained with the different regularization methods, and for the different parameters derived using the different criteria. While both methods can yield good maps for a range of regularization parameters, in the Tikhonov method the suppression of noisy modes are more gradually applied, produce more smooth maps which avoids some visual artefacts in the maps generated with the TSVD method.