The Growth Rate of Cosmic Structure from Peculiar Velocities at Low and High Redshifts
Abstract
Peculiar velocities are an important probe of the growth rate of mass density fluctuations in the universe. Most previous studies have focused exclusively on measuring peculiar velocities at intermediate (0.2 < z < 1) redshifts using statistical redshift-space distortions. Here, we emphasize the power of peculiar velocities obtained directly from distance measurements at low redshift (z <~ 0.05), and show that these data break the usual degeneracies in the Ωm, 0- σ8, 0 parameter space. Using only peculiar velocity data, we find {\Omega _{{m},0}}= 0.259+/- 0.045 and σ8, 0 = 0.748 ± 0.035. Fixing the amplitude of fluctuations at very high redshift using observations of the cosmic microwave background, the same data can be used to constrain the growth index γ, with the strongest constraints coming from peculiar velocity measurements in the nearby universe. We find γ = 0.619 ± 0.054, consistent with ΛCDM. Current peculiar velocity data already strongly constrain modified gravity models and will be a powerful test as data accumulate.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2012
- DOI:
- 10.1088/2041-8205/751/2/L30
- arXiv:
- arXiv:1203.4814
- Bibcode:
- 2012ApJ...751L..30H
- Keywords:
-
- cosmological parameters;
- cosmology: observations;
- cosmology: theory;
- distance scale;
- galaxies: distances and redshifts;
- gravitation;
- large-scale structure of universe;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 5 pages, 3 figures, 2 tables. ApJ Letters, in press. Updated analysis now includes BOSS and 6dFGS data