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| This shows the statistics for an ALMA observation covering all 8 GHz centered on 339 GHz in the LSB. In each pointing, 2 hours of integration will reach a two sigma noise level of about 18 microJy for 64 antennas (Butler and Wootten ALMA Memo 276); the mosaicked field we have simulated to increase statistics covers 2.6 x 2.6 arcminutes. The IRAS-based luminosity function published by the Saunders et al. (MNRAS 242, 318 1990) 60 micron luminosity function was used to generate a sample of galaxies variously distributed in distance and flux for H0=75 and q0=0.5. The galaxies are binned into flux density intervals. The red lines show the number of antennas in an array which would reach the two sigma level marked in two hours. Note that the numver of distant galaxies detected by ALMA more than doubles as the number of antennas is incremented by 50%. Note also that to create this field, over 200 pointings of the array must be made, each of two hours duration--this is a fairly lengthy integration in totality. On average, one normal Milky-Way type galaxy is imaged by the ALMA in every two fields, or four hours of integration--a typical integration period in the submillimeter, where imaging must be done within a few hours of the source passing overhead, owing to atmospheric absorption. |