The WiggleZ Dark Energy Survey: probing the epoch of radiation domination using large-scale structure

Abstract

We place the most robust constraint to date on the scale of the turnover in the cosmological matter power spectrum using data from the WiggleZ Dark Energy Survey. We find this feature to lie at a scale of k 0 =0.0160 +0.0041 −0.0035 [h/Mpc] (68% confidence) for an effective redshift of z eff =0.62 and obtain from this the firstever turnover-derived distance and cosmology constraints: a measure of the cosmic distance-redshift relation in units of the horizon scale at the redshift of radiationmatter equality (r H ) of D V (z eff =0.62)/r H =18.3 +6.3 −3.3 and, assuming a prior on the number of extra relativistic degrees of freedom N eff =3, constraints on the cosmological matter density parameter Ω M h 2 =0.136 +0.026 −0.052 and on the redshift of matter-radiation equality z eq =3274 +631 −1260 . We stress that these results are obtained within the theoretical framework of Gaussian primordial fluctuations and linear large-scale bias. With this caveat, all results are in excellent agreement with the predictions of standard ΛCDM models. Our constraints on the logarithmic slope of the power spectrum on scales larger than the turnover is bounded in the lower limit with values only as low as −1 allowed, with the prediction of P (k)∝k from standard ΛCDM models easily accommodated by our results. Lastly, we generate forecasts to estimate the achievable precision of future surveys at constraining k 0 , Ω M h 2 , z eq and N eff . We find that the Baryon Oscillation Spectroscopic Survey (BOSS) should substantially improve upon the WiggleZ turnover constraint, reaching a precision on k 0 of ±9% (68% confidence), translating to precisions on Ω M h 2 and z eq of ±10% (assuming a prior N eff =3) and on N eff of +78 −56 % (assuming a prior Ω M h 2 =0.135). This represents sufficient precision to sharpen the constraints on N eff from WMAP, particularly in its upper limit. For Euclid, we find corresponding attainable precisions on (k 0 , Ω M h 2 , N eff ) of (3, 4, +17 −21 )%. This represents a precision approaching our forecasts for the Planck Surveyor.

Evolution of Density Parameters on a Smooth Embedded Universe

“…For these cases, the difference between the curves with different values of β 0 are not evident and the curves are overlapped with those generated from CDM. Moreover, the equivalence matter-radiation redshift z mr is around 3391 in accordance with [36,59].…”

Viscous cold dark matter in agreement with observations

“…Since the peak of the matter power spectrum is sensitive to z eq , large scale structure surveys can, in principle, constraint such value. Recently, the Wig-gleZ project has provided the first constraints on this quantity [45]. Although the large uncertainty, their results are consistent with the standard value z eq ∼ 3000.…”

Degeneracy between warm and coupled cold dark matter: A clarifying note

“…If galaxy surveys are able to probe very large volumes then k eq can be used to constrain cosmological models. Unfortunately, we have so far only moderate bounds on the turnover scale provided by the WiggleZ survey k eq = 0.0160 +0.0035 −0.0041 h Mpc −1 [16]. Therefore, since we have in general Ω w =Ω c we expect that the k eq will differ in both models.…”