Spectroscopy and photometry of elliptical galaxies - A large-scale streaming motion in the local universe

The authors present results from a study of the distances and velocities of elliptical galaxies out to ≡6000 km s⁻¹. Distances are inferred from a new relation between central velocity dispersion and an angular diameter defined by integrated surface brightness. With this residual velocities Vobs - Vpred from a smooth Hubble flow are estimated. It is found that Vobs - Vpred, in coordinates with respect to the microwave background, exhibits a systematic variation over the celestial sphere. Interpreted as a large-scale bulk flow, this variation implies a mean motion of the ellipticals with respect to the microwave background of 599±104 km s⁻¹ in the direction l = 312°±11°, b = 6°±10°. The data show that if the microwave dipole anisotropy is due to a motion of the Local Group of ≡600 km s⁻¹, as conventionally interpreted, this motion is not primarily the result of gravitational acceleration by local (V < 5000 km s⁻¹) mass concentrations.