Wilkinson Microwave Anisotropy Probe Results Research Articles

On the statistical significance of the bulk flow measured by thePlancksatellite

A recent analysis of data collected by the Planck satellite detected a net dipole at the location of X-ray selected galaxy clusters, corresponding to a large-scale bulk flow extending at least to $z\sim 0.18$, the median redshift of the cluster sample. The amplitude of this flow, as measured with Planck, is consistent with earlier findings based on data from the Wilkinson Microwave Anisotropy Probe (WMAP). However, the uncertainty assigned to the dipole by the Planck team is much larger than that found in the WMAP studies, leading the authors of the Planck study to conclude that the observed bulk flow is not statistically significant. We here show that two of the three implementations of random sampling used in the error analysis of the Planck study lead to systematic overestimates in the uncertainty of the measured dipole. Random simulations of the sky do not take into account that the actual realization of the sky leads to filtered data that have a 12% lower root-mean-square dispersion than the average simulation. Using rotations around the Galactic pole (the Z axis), increases the uncertainty of the X and Y components of the dipole and artificially reduces the significance of the dipole detection from 98-99% to less than 90% confidence. When either effect is taken into account, the corrected errors agree with those obtained using random distributions of clusters on Planck data, and the resulting statistical significance of the dipole measured by Planck is consistent with that of the WMAP results.

Observational constraints on the new generalized Chaplygin gas model

We use the latest data to investigate observational constraints on the new generalized Chaplygin gas (NGCG) model. Using the Markov Chain Monte Carlo method, we constrain the NGCG model with type Ia supernovae from the Union2 set (557 data), the usual baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey data release 7 galaxy sample, the cosmic microwave background observation from the 7-year Wilkinson Microwave Anisotropy Probe results, newly revised data on H(z), as well as a value of θBAO (z = 0.55) = (3.90° ± 0.38°) for the angular BAO scale. The constraint results for the NGCG model are ωX = −1.0510+0.1563−0.1685(1σ)+0.2226−0.2398(2σ), η=1.0117+0.0469−0.0502(1σ)+0.0693−0.0716(2σ) and ΩX=0.7297+0.0229−0.0276(1σ)+0.0329−0.0402(2σ), which give a rather stringent constraint. From the results, we can see that a phantom model is slightly favored and the probability that energy transfers from dark matter to dark energy is a little larger than the inverse.

Search for a resonant enhancement of the7Be +dreaction and primordial7Li abundances

Big Bang nucleosynthesis calculations, constrained by the Wilkinson Microwave Anisotropy Probe results, produce ${}^{7}$Li abundances almost a factor of four larger than those extrapolated from observations. Since primordial ${}^{7}$Li is believed to be mostly produced by the beta decay of ${}^{7}$Be, one proposed solution to this discrepancy is a resonant enhancement of the ${}^{7}$Be($d,p$)2$\ensuremath{\alpha}$ reaction rate through the 5/2${}^{+}$ 16.7-MeV state in ${}^{9}$B. The ${}^{2}$H(${}^{7}$Be,$d$)${}^{7}$Be reaction was used to search for such a resonance; none was observed. An upper limit on the width of the proposed resonance was deduced.

THE LOCAL DUST FOREGROUNDS IN THE MICROWAVE SKY. I. THERMAL EMISSION SPECTRA

Analyses of the cosmic microwave background (CMB) radiation maps made by the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed anomalies not predicted by the standard inflationary cosmology. In particular, the power of the quadrupole moment of the CMB fluctuations is remarkably low, and the quadrupole and octopole moments are aligned mutually and with the geometry of the Solar system. It has been suggested in the literature that microwave sky pollution by an unidentified dust cloud in the vicinity of the Solar system may be the cause for these anomalies. In this paper, we simulate the thermal emission by clouds of spherical homogeneous particles of several materials. Spectral constraints from the WMAP multi-wavelength data and earlier infrared observations on the hypothetical dust cloud are used to determine the dust cloud's physical characteristics. In order for its emissivity to demonstrate a flat, CMB-like wavelength dependence over the WMAP wavelengths (3 through 14 mm), and to be invisible in the infrared light, its particles must be macroscopic. Silicate spheres from several millimetres in size and carbonaceous particles an order of magnitude smaller will suffice. According to our estimates of the abundance of such particles in the Zodiacal cloud and trans-neptunian belt, yielding the optical depths of the order of 1E-7 for each cloud, the Solar-system dust can well contribute 10 microKelvin (within an order of magnitude) in the microwaves. This is not only intriguingly close to the magnitude of the anomalies (about 30 microKelvin), but also alarmingly above the presently believed magnitude of systematic biases of the WMAP results (below 5 microKelvin) and, to an even greater degree, of the future missions with higher sensitivities, e.g. PLANCK.

Understanding the WMAP Results: Low-Order Multipoles and Dust in the Vicinity of the Solar System

Analyses of the cosmic microwave background (CMB) radiation maps produced by the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed anomalies not predicted by the standard cosmological theory. It has been suggested that a dust cloud in the vicinity of the Solar system may be the cause for these anomalies. In this paper, the thermal emission by particles from two known interplanetary meteoroid complexes is tested against the CMB maps. Conclusions are drawn based on the geometry of cloud projections onto the WMAP sky whether these clouds are likely to explain the observed anomaly. The smooth background Zodiacal cloud and one of the Taurid meteor complex branches do not explain the WMAP anomaly.

A new analysis of the Poincaré dodecahedral space model

Context. The full three-year Wilkinson Microwave Anisotropy Probe results (hereafter WMAP3) reinforce the absence of large-angle correlations at scales greater than 60 ◦ . The Poincare dodecahedral space model, which may naturally explain such features, thus remains a plausible cosmological model, despite recent controversy about whether matched circle searches would or would not push the topology beyond the horizon. Aims. We have used new eigenmode calculations of the dodecahedral space to predict the cosmic microwave background (CMB) temperature anisotropies in such a model, with an improved angular resolution. Methods. We have simulated CMB maps and exhibited the expected self intersection of the last scattering surface along six pairs of circles. For a set of plausible cosmological parameters, we have derived the angular power spectrum of the CMB up to large wavenumbers. Results. Comparison of the angular power spectrum with the WMAP3 observations leads to an optimal fit with the Poincare dodecahedral space model, for a value Ωtot = 1.018 of the total energy density parameter.

Constraining the Cold Dark Matter Spectrum Normalization in Flat Dark Energy Cosmologies

We study the relation between the rms mass fluctuations on 8 h-1 Mpc scales and Ωm using the recent clustering results of XMM-Newton soft (0.5-2 keV) X-ray sources, which have a median redshift of z ~ 1.2. The relation can be represented in the form σ8 = 0.34(±0.01)Ω, where γ ≡ γ(Ωm, w), and it is valid for all w < - models. By combining the X-ray clustering and SN Ia data we find that the model that best reproduces the observational data is that with Ωm 0.26, w -0.90, and σ8 0.73, which is in excellent agreement with the recent 3 yr Wilkinson Microwave Anisotropy Probe results.

Relic keV Sterile Neutrinos and Reionization

A sterile neutrino with a mass of several keV can account for cosmological dark matter, as well as explain the observed velocities of pulsars. We show that x rays produced by the decays of these relic sterile neutrinos can boost the production of molecular hydrogen, which can speed up the cooling of gas and the early star formation, which can, in turn, lead to a reionization of the Universe at a high enough redshift to be consistent with the Wilkinson Microwave Anisotropy Probe results.

The end of the dark ages in modified Newtonian dynamics

We study the evolution of a spherically symmetric density perturbation in the Modified Newtonian Dynamics model applied to the net acceleration over Hubble flow. The background cosmological model is a A-dominated, low-Ω b Friedmann model with no cold dark matter. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that under these assumptions the first low-mass objects (M ≤ 3 × 10 4 M○.) may collapse already for z ∼ 30, which is in quite good agreement with the recent Wilkinson Microwave Anisotropy Probe results. A lower value of a 0 would lead to much slower collapse of such objects.

WMAP and supergravity inflationary models

We study a class of $N=1$ supergravity inflationary models in which the evolution of the inflaton dynamics is controlled by a single power in the inflaton field at the point where the observed density fluctuations are produced, in the context of the braneworld scenario, in light of Wilkinson Microwave Anisotropy Probe results. In particular, we find that the bounds on the spectral index and its running constrain the parameter space both for models where the inflationary potential is dominated by a quadratic term and by a cubic term in the inflaton field. We also find that ${\ensuremath{\alpha}}_{s}g0$ is required for the quadratic model whereas ${\ensuremath{\alpha}}_{s}l0$ for the cubic model. Moreover, we have determined an upper bound on the five-dimensional Planck scale, ${M}_{5}\ensuremath{\lesssim}0.019\mathrm{M},$ for the quadratic model. On the other hand, a running spectral index with ${n}_{s}g1$ on large scales and ${n}_{s}l1$ on small scales is not possible in either case.

The statistical significance of the low cosmic microwave background mulitipoles

The Wilkinson Microwave Anisotropy Probe (WMAP) has measured lower amplitudes for the temperature quadrupole and octopole anisotropies than expected in the best fitting (concordance) A-dominated cold dark matter (ACDM) cosmology. Some authors have argued that this discrepancy may require new physics. However, the statistical significance of this result is not clear. Some authors have applied frequentist arguments and claim that the discrepancy would occur by chance about 1 time in 700, if the concordance model is correct. Other authors have used Bayesian arguments to claim that the data show marginal evidence for new physics. I investigate these confusing and apparently conflicting claims in this Letter using a frequentist analysis and a simplified Bayesian analysis. On either analysis, I conclude that the WMAP results are consistent with the concordance ACDM model.

The WMAP data and results

The Wilkinson Microwave Anisotropy Probe (WMAP) science team has released results from the first year of operation at the Earth–Sun L 2 Lagrange point. The maps are consistent with previous observations but have much better sensitivity and angular resolution than the COBE DMR maps, and much better calibration accuracy and sky coverage than ground-based and balloon-borne experiments. The angular power spectra from these ground-based and balloon-borne experiments are consistent within their systematic and statistical uncertainties with the WMAP results. WMAP detected the large angular-scale correlation between the temperature and polarization anisotropies of the CMB caused by electron scattering since the Universe became reionized after the “Dark Ages”, giving a value for the electron scattering optical depth of 0.17 ± 0.04. The simplest ΛCDM model with n=1 and Ω tot =1 fixed provides an adequate fit to the WMAP data and gives parameters which are consistent with determinations of the Hubble constant and observations of the accelerating Universe using supernovae. The time-ordered data, maps, and power spectra from WMAP can be found at http://lambda.gsfc.nasa.gov along with 13 papers by the WMAP science team describing the results in detail.

Star Formation at the Twilight of the Dark Ages: Which Stars Reionized the Universe?

We calculate the global star formation rate density (SFRD) from z ~ 30-3 using a semianalytic model incorporating the hierarchical assembly of dark matter halos, gas cooling via atomic hydrogen, star formation, supernova feedback, and suppression of gas collapse in small halos due to the presence of a photoionizing background. We compare the results with the predictions of simpler models based on the rate of dark matter halo growth and a fixed ratio of stellar to dark mass, and with observational constraints on the SFRD at 3 z 6. We also estimate the star formation rate due to very massive, metal-free Population III stars using a simple model based on the halo formation rate, calibrated against detailed hydrodynamic simulations of Population III star formation. We find that the total production rate of hydrogen-ionizing photons during the probable epoch of reionization (15 z 20) is approximately equally divided between Population II and Population III stars, and that if reionization is late (zreion 15, close to the lower limit of the range allowed by the Wilkinson Microwave Anisotropy Probe results), then Population II stars alone may be able to reionize the universe.