1203.4814 (Michael J. Hudson et al.)

The growth rate of cosmic structure from peculiar velocities at low and high redshifts    [PDF]

Michael J. Hudson, Stephen J. Turnbull

Peculiar velocities are an important probe of the growth rate of mass density fluctuations in the Universe. Most previous studies have focussed exclusively on measuring peculiar velocities at intermediate ($0.2 < z < 1$) redshifts using statistical redshift-space distortions. Here we emphasize the power of direct peculiar velocity measurements at low redshift ($z < 0.1$), and show that these data break the usual degeneracies in the \Omzero - $\sigma_{8,0}$ parameter space. Doing so, we find parameters consistent with \LCDM{}. Fixing the amplitude of fluctuations at very high redshift using observations of the Cosmic Microwave Background (CMB), the same data can be used to constrain the growth parameter $\gamma$, with the strongest constraints coming from direct peculiar velocity measurements in the nearby Universe. We find $\gamma = 0.607\pm 0.053$, consistent with \LCDM{} but also with braneworld gravity.

View original: http://arxiv.org/abs/1203.4814