Possible Detection of Baryonic Fluctuations in the Large‐Scale Structure Power Spectrum

Open Access
Publisher Website
Google Scholar
Abstract
We present a joint analysis of the power spectra of density fluctuations from three independent cosmological redshift surveys: the IRAS Point Source redshift catalog (PSCz) galaxy survey, the Automated Plate Measuring Machine (APM) galaxy cluster catalog, and the Abell/ACO cluster survey. Over the range 0.03 h Mpc-1 ≤ k ≤ 0.15 h Mpc-1, the amplitudes of these three power spectra are related through a simple linear-biasing model with b = 1.5 and b = 3.6 for Abell/ACO versus APM and Abell/ACO versus PSCz, respectively. Furthermore, the shape of these power spectra are remarkably similar despite the fact that they are comprised of significantly different objects (individual galaxies through to rich clusters). Individually, each of these surveys shows visible evidence for "valleys" in their power spectra—i.e., departures from a smooth featureless spectrum—at similar wavenumbers. We use a newly developed statistical technique called the false discovery rate to show that these valleys are statistically significant. One favored cosmological explanation for such features in the power spectrum is the presence of a nonnegligible baryon fraction (Ωb) in the universe, which causes acoustic oscillations in the transfer function of adiabatic inflationary models. We have performed a maximum likelihood marginalization over four important cosmological parameters of this model (Ωm, Ωb, ns, and H0). We use a prior on H0 = 69 ± 15 and find Ωmh2 = 0.12, Ωbh2 = 0.029, and ns = 1.08 (2 σ confidence limits), which are fully consistent with the favored values of these cosmological parameters from the recent cosmic microwave background (CMB) experiments. This agreement strongly suggests that we have detected baryonic oscillations in the power spectrum of matter at a level expected from a cold dark matter model normalized to fit these CMB measurements.