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

Abstract

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 $\beta_{K}=\Omega\sbr{m}^{0.6}/b_{K}$. Taken together the best fit $\beta_{K} = 0.49 \pm 0.04$. We explore the effects of morphology on the determination of $\beta$ 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 $b\sbr{E}/b\sbr{S} \sim 1.6$. The density fluctuations of 2MASS galaxies in $8 h^{-1}$ Mpc spheres in the local volume is found to be $\sigma\sbr{8,K} = 0.9$. From this result and our value of $\beta_{K}$, we find $\sigma_8 (\Omega\sbr{m}/0.3)^{0.6} = 0.91\pm0.12$. 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 $\sigma_8 (\Omega\sbr{m}^/0.3)^{0.6} = 0.85\pm0.05$.