Return to the Great Attractor: Strong Evidence for a Steradian-sized Flow Converging at ∼70 Mpc within the GA Supercluster and Aligned with the CMB Dipole

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We used the FourStar near-IR camera on Magellan–Baade to obtain high signal-to-noise ratio H -band imaging of 66 galaxies with radial velocities of 2000 km s –1 ≤ V ≤ 5000 km s −1 . Our goal was to use the superior distance measurements of surface brightness fluctuations (SBFs) to derive “peculiar velocities” to test earlier claims that the cosmic microwave background (CMB) dipole anisotropy, equivalent to ≈600 km s −1 with respect to the Local Group, arises from a “local” overdensity in the galaxy/dark matter distribution—the Great Attractor (GA). The ability to use SBFs to measure distances with ∼5% accuracy confirms a strong flow over a steradian of the sky peaking at V pec ∼ 1000 km s −1 and converging to zero at D ≈ 70 Mpc from the Local Group. The modest spatial extent of this flow, R V ≈ 5000 km s −1 , is consistent with the original GA model (diameter D ≲ 140 Mpc), as well as the magnitude and direction of the CMB dipole anisotropy and the power spectrum of CMB fluctuations—the last two arguably the most secure measurements in astrophysics. In contrast, our results are at odds with reports of comparable amplitude “bulk flows” on scales of hundreds of Mpc that themselves may be inconsistent with the expected fluctuations in the CMB for a ΛCDM Universe. We contend that only distance estimators as accurate as SBFs are able to settle the question of whether the CMB dipole arises from the gravitational influence of large-scale structure within or beyond ∼100 Mpc of the Local Group.