Mapping the large-scale anisotropy in the WMAP data

The Astrophysical Journal, 1997

We study the anisotropy of the cosmic microwave background (CMB) in cold and mixed dark matter (CDM and MDM) models, with non scale-invariant primordial power spectra (i.e. n = 1) and a late, sudden reionization of the intergalactic medium at redshift z rh . We test these models against recent detections of CMB anisotropy at large and intermediate angular scales. We find that current CMB anisotropy measurements cannot discriminate between CDM and MDM models. Our likelihood analysis indicates that models with blue power spectra (n ≃ 1.2) and a reionization at z rh ∼ 20 are most consistent with the anisotropy data considered here. Without reionization our analysis gives 1.0 ≤ n ≤ 1.26 (95% C.L.) for Ω b = 0.05.

The Astrophysical Journal, 2004

We report on the results from two independent but complementary statistical analyses of the WMAP first-year data, based on the power spectrum and N-point correlation functions. We focus on large and intermediate scales (larger than about 3 •) and compare the observed data against Monte Carlo ensembles with WMAP-like properties. In both analyses, we measure the amplitudes of the large-scale fluctuations on opposing hemispheres and study the ratio of the two amplitudes. The power-spectrum analysis shows that this ratio for WMAP, as measured along the axis of maximum asymmetry, is high at the 95%-99% level (depending on the particular multipole range included). The axis of maximum asymmetry of the WMAP data is weakly dependent on the multipole range under consideration but tends to lie close to the ecliptic axis. In the N-point correlation function analysis we focus on the northern and southern hemispheres defined in ecliptic coordinates, and we find that the ratio of the large-scale fluctuation amplitudes is high at the 98%-99% level. Furthermore, the results are stable with respect to choice of Galactic cut and also with respect to frequency band. A similar asymmetry is found in the COBE-DMR map, and the axis of maximum asymmetry is close to the one found in the WMAP data. Subject headings: cosmic microwave background-cosmology: observations-methods: statistical

Nature, 1992

The cosmic microwave background (CMB) is one of only a few physically observable remnants of the early Universe. Studies of the spectrum, polarization and spatial distribution of the CMB can potentially lead to a detailed understanding of the processes that took place in the early Universe. Many of the outstanding cosmological questions regarding the age, contents, future, and large scale dynamics of the universe are addressed in these studies. In particular, measurements of the spatial anisotropy of the CMB are a very effective method for testing and constraining models of cosmic structure formation.

Space Sciences Series of ISSI, 2002

This paper discusses the status of observations of Cosmic Microwave Background (CMB) anisotropies. The first detections of primary anisotropies in the CMB, achieved about 10 years ago, boosted a large number of ground-based and balloon-borne experiments that have delineated the CMB angular power spectrum up to spherical harmonic multipole ∼ 1000. A wealth of information on cosmological parameters is being revealed by these measurements. Very recently, the positions and amplitudes of the first and second peak in the power spectrum have been determined providing strong support to inflationary models with adiabatic primordial density perturbations. A total density equal to the critical value, and baryonic density consistent with Big Bang nucleosynthesis are the first results emerging from the current CMB data. Future experiments on ground (mainly interferometers), in balloons and from space (MAP and Planck missions) have the potential to constrain more than 10 cosmological parameters with high precision.

Arxiv preprint astro-ph/9404072, 1994

We present results from two four-frequency observations centered near the stars Sigma Hercules and Iota Draconis during the fourth flight of the Millimeter-wave Anisotropy eXperiment (MAX). The observations were made of 6° x 0°.6 strips of the sky with a 1°.4 peak to peak sinusoidal chop in all bands. The FWHM beam sizes were 0°.55±0°.05 at 3.5 cm-1 and a 0°.75±0°.05 at 6, 9, and 14 cm-1. Significant correlated structures were observed at 3.5, 6 and 9 cm-1. The spectra of these signals are inconsistent with thermal emission from known interstellar dust populations. The extrapolated amplitudes of synchrotron and free-free emission are too small to account for the amplitude of the observed structures. If the observed structures are attributed to CMB anisotropy with a Gaussian autocorrelation function and a coherence angle of 25', then the most probable values are ∆T/T CMB = 3.1 −1.3 +1.7 × 10 −5 for the Sigma Hercules scan, and ∆T/T CMB = 3.3 −1.1 +1.1 × 10 −5 for the Iota Draconis scan (95% confidence upper and lower limits).

Pramana, 2004

The breakdown of statistical homogeneity and isotropy of cosmic perturbations is a generic feature of ultra large scale structure of the cosmos, in particular, of non trivial cosmic topology. The statistical isotropy (SI) of the Cosmic Microwave Background temperature fluctuations (CMB anisotropy) is sensitive to this breakdown on the largest scales comparable to, and even beyond the cosmic horizon. We propose a set of measures, κ ℓ (ℓ = 1, 2, 3, . . .) which for non-zero values indicate and quantify statistical isotropy violations in a CMB map. We numerically compute the predicted κ ℓ spectra for CMB anisotropy in flat torus universe models. Characteristic signature of different models in the κ ℓ spectrum are noted.

The Astrophysical Journal, 1994

In many cosmological models, the large angular scale anisotropy in the cosmic microwave background is parameterized by a spectral index, n, and a quadrupolar amplitude, Q. For a Peebles-Harrison-Zel'dovich spectrum, n = 1. Using data from the Far Infra-Red Survey (FIRS) and a new statistical measure, a contour plot of the likelihood for cosmological models for which −1 < n < 3 and 0 ≤ Q ≤ 50 µK is obtained. We find that the likelihood is maximum at (n, Q) = (1.0, 19 µK). For constant n the likelihood falls to half its maximum at Q ≈ 14 µK and 25 µK and for constant Q the likelihood falls to half its maximum at n ≈ 0.5 and 1.4. Regardless of Q, the likelihood is always less than half its maximum for n < −0.4 and for n > 2.2, as it is for Q < 8 µK and Q > 44 µK.

Astrophysical Journal, 2001

We extend the analysis of the MAXIMA-1 cosmic microwave background (CMB) data to smaller angular scales. MAXIMA, a bolometric balloon experiment, mapped a 124 deg$^2$ region of the sky with 10\arcmin resolution at frequencies of 150, 240 and 410 GHz during its first flight. The original analysis, which covered the multipole range $36 \leq \ell \leq 785$, is extended to $\ell = 1235$ using data from three 150 GHz photometers in the fully cross-linked central 60 deg$^2$ of the map. The main improvement over the original analysis is the use of 3\arcmin square pixels in the calculation of the map. The new analysis is consistent with the original for $\ell < 785$. For $\ell > 785$, where inflationary models predict a third acoustic peak, the new analysis shows power with an amplitude of $56 \pm 7$ \microk at $\ell \simeq 850$ in excess to the average power of $42 \pm 3$ \microk in the range $441 < \ell < 785$.

2003

Several experiments (including BOOMERanG, MAXIMA, DASI, VSA, CBI) have recently detected very low contrast structures in the Cosmic Microwave Background (CMB), the otherwise isotropic radiation coming from the early Universe. These structures have a contrast of the order of 25 ppm and a dominant angular size of one degree. In the current cosmological model, these structures result from acoustic oscillations of the primeval plasma within the horizon at recombination (z ∼ 1100). In the framework of the Hot Big Bang theory with the inflationary hypothesis, the statistical properties of the image of the CMB allow us to measure most of the cosmological parameters.

The Astrophysical Journal, 1993

We report a measurement of anisotropy in the cosmic microwave background radiation (CMBR) on 7@È22@ scales. Observations of 36 Ðelds near the North Celestial Pole (NCP) were made at 31.7 and 14.5 GHz, using the 5.5 m and 40 m telescopes at the Owens Valley Radio Observatory (OVRO) from 1993 to 1996. Multiepoch VLA observations at 8.5 and 15 GHz allow removal of discrete source contamination. After point-source subtraction, we detected signiÐcant structure, which we identify with emission from a combination of a steep-spectrum foreground and the CMBR. The foreground component is found to correlate with IRAS 100 km dust emission. Lack of Ha emission near the NCP suggests that this foreground is either high-temperature thermal bremsstrahlung K), Ñat-spectrum synchro-(T e Z 106 tron, or an exotic component of dust emission. On the basis of low-frequency maps of the NCP, we can restrict the spectral index of the foreground to b º [2.2. Although the foreground signal dominates at 14.5 GHz, the extracted CMBR component contributes 88% of the variance at 31.7 GHz, yielding an rms Ñuctuation amplitude of kK, including 4.3% calibration uncertainty and 12% sample 82~9 .1 12.1 variance (68% conÐdence). In terms of the angular power spectrum, averaged over a range C l \ S o a l m o2T, of multipoles l \ 361È756, the detected broadband amplitude is kK. dT le 4 [l(l ] 1)C l /(2n)]1@2 \ 59~6 .5 8.6 This measurement, when combined with small angular scale upper limits obtained at the OVRO, indicates that the CMBR angular power spectrum decreases between l D 600 and l D 2000 and is consistent with Ñat cosmological models. Subject headings : cosmic microwave background È cosmology : observations