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Caption: Figure 3.
Expected EHT Fourier space coverage on Sgr A*. The left panel shows both detections (red) and non-detections (gray) of Sgr A* in the 2013 EHT campaign. Participating telescopes were: APEX, CARMA, JCMT, SMA, and SMT. The dashed circles mark baselines with a fringe spacing equal to 50 μas (approximately the diameter of the shadow of the SMBH candidate Sgr A*) and 25 μas. The two remaining panels show simulated EHT observations in 2020: (1) without ALMA and (2) with ALMA. Specifications to determine baseline detections shown are those detailed in Section 2.2. These figures emphasize the benefit of including ALMA in the array: its high sensitivity allows detections for SgrA* on all observed baselines. Because each EHT site requires at least one strong baseline to identify an interferometric fringe and to correct for residual delays, rates, and phase wander, ALMA significantly extends the Fourier coverage and sensitivity even for non-ALMA baselines. Coverage shown in the two right panels corresponds to an array including Chile (APEX, ALMA), Mexico (LMT), France (NOEMA), Spain (PV), Hawaii (SMA, JCMT), Arizona (SMT), and South Pole (SPT). The corresponding baseline coverage of the 2017 observations is shown in Figure 11.
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