ALMA Memo No. 374 Wide Field Imagings with the Atacama Large Millimter/ Submillimeter Array

Image quality of wide field observations with the ALMA has been studied with imaging simulations. Results of the simulations showed that antenna pointing errors are a serious problem for obtaining high quality images because they make a large error in visibilities in the central (u,v) hole estimated by mosaicing data processings. The ALMA Compact Array (ACA) with more than 10 smaller dishes (6-8m) can compensate this problem. However, a carefull treatment of adding the data measured with the ACA to the data from the ALMA is needed to obtain a significant improvement of imaging performances. The ACA with 6m antennas has better imaging performances than that of the ACA with 8 m antennas, although the difference between them is small for noisy cases. Another option to realize high fidelity images for large objects is to improve the pointing of some or all of the 12 m antennas.