2005ApJ...635...11P

We compare the peculiar velocity field within 65 h^–1 Mpc predicted from 2MASS photometry and public redshift data to three independent peculiar velocity surveys based on Type Ia supernovae, surface brightness fluctuations in elliptical galaxies, and Tully-Fisher distances to spiral galaxies. The three peculiar velocity samples are each in good agreement with the predicted velocities and produce consistent results for β_K=Ω^0.6_m/b_K. Taken together, the best-fit β_K=0.49±0.04. We explore the effects of morphology on the determination of β by splitting the 2MASS sample into E+S0 and S+Irr density fields and find that both samples are equally good tracers of the underlying dark matter distribution, but that early types are more clustered, by a relative factor b_E/b_S∼1.6. The density fluctuations of 2MASS galaxies in 8 h^–1 Mpc spheres in the local volume is found to be σ_8,K=0.9. From this result and our value of β_K, we find σ₈(Ω_m/0.3)^0.6=0.91±0.12. This is in excellent agreement with results from the IRAS redshift surveys, as well as other cosmological probes. Combining the 2MASS and IRAS peculiar velocity results yields σ₈(Ω_m/0.3)^0.6=0.85±0.05.