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The Tianlai cylinder pathfinder is a radio interferometer array to test 21 cmintensity mapping techniques in the post-reionization era. It works in passivedrift scan mode to survey the sky visible in the northern hemisphere. To dealwith the large instantaneous field of view and the spherical sky, we decomposethe drift scan data into m-modes, which are linearly related to the skyintensity. The sky map is reconstructed by solving the linear interferometerequations. Due to incomplete uv coverage of the interferometer baselines, thisinverse problem is usually ill-posed, and regularization method is needed forits solution. In this paper, we use simulation to investigate two frequentlyused regularization methods, the Truncated Singular Value Decomposition (TSVD),and the Tikhonov regularization techniques. Choosing the regularizationparameter is very important for its application. We employ the generalizedcross validation (GCV) method and the L-curve method to determine the optimalvalue. We compare the resulting maps obtained with the different regularizationmethods, and for the different parameters derived using the different criteria.While both methods can yield good maps for a range of regularizationparameters, in the Tikhonov method the suppression of noisy modes are moregradually applied, produce more smooth maps which avoids some visual artefactsin the maps generated with the TSVD method.

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