Cosmological Parameters from the Comparison of the 2MASS Gravity Field with Peculiar Velocity Surveys

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 ellipticals, and Tully-Fisher distances to spirals. The three peculiar velocity samples are each in good agreement with the predicted velocities and produce consistent results for βK=Ωm0.6/bK. Taken together the best fit βK = 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 both samples are equally good tracers of the underlying dark matter distribution, but that early-types are more clustered by a relative factor bE/bS ~ 1.6. The density fluctuations of 2MASS galaxies in 8 h⁻¹ Mpc spheres in the local volume is found to be σ8,K = 0.9. From this result and our value of βK, we find σ₈ (Ωm/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 (Ωm^/0.3)0.6 = 0.85±0.05.