Extended Mosaic Observations with the Cosmic Background Imager (original) (raw)
Related papers
2008
Using the Cosmic Background Imager, a 13-element interferometer array operating in the 26-36 GHz frequency band, we have observed 40 deg 2 of sky in three pairs of fields, each ∼ 145 ′ × 165 ′ , using overlapping pointings (mosaicing). We present images and power spectra of the cosmic microwave background radiation in these mosaic fields. We remove ground radiation and other low-level contaminating signals by differencing matched observations of the fields in each pair. The primary foreground contamination is due to point sources (radio galaxies and quasars). We have subtracted the strongest sources from the data using higher-resolution measurements, and we have projected out the response to other sources of known position in the power-spectrum analysis. The images show features on scales ∼ 6 ′-15 ′ , corresponding to masses ∼ 5-80 × 10 14 M ⊙ at the surface of last scattering, which are likely to be the seeds of clusters of galaxies. The power spectrum estimates have a resolution ∆ℓ ≈ 200 and are consistent with earlier results in the multipole range ℓ 1000. The power spectrum is detected with high signal-to-noise ratio in the range 300 ℓ 1700. For 1700 ℓ 3000 the observations are consistent with the results from more sensitive CBI deep-field observations. The results agree with the extrapolation of cosmological models fitted to observations at lower ℓ, and show the predicted drop at high ℓ (the "damping tail"). Subject headings: cosmic microwave background-cosmology: observations-techniques: interferometric
Cosmic microwave background anisotropy power spectrum statistics for high precision cosmology
Physical Review D, 2001
As the era of high precision cosmology approaches, the empirically determined power spectrum of the microwave background anisotropy, C l , will provide a crucial test for cosmological theories. We present a unified semi-analytic framework for the study of the statistical properties of the C l coefficients computed from the results of balloon, ground based, and satellite experiments. An illustrative application shows that commonly used approximations bias the estimation of the baryon parameter Ω b at the 1% level even for a satellite capturing as much as ∼ 70% of the sky.
Measurements of secondary cosmic microwave background anisotropies with the South Pole Telescope
The Astrophysical …, 2010
We report cosmic microwave background (CMB) power spectrum measurements from the first 100 deg 2 field observed by the South Pole Telescope (SPT) at 150 and 220 GHz. On angular scales where the primary CMB anisotropy is dominant, 3000, the SPT power spectrum is consistent with the standard ΛCDM cosmology. On smaller scales, we see strong evidence for a point source contribution, consistent with a population of dusty, star-forming galaxies. After we mask bright point sources, anisotropy power on angular scales of 3000 < < 9500 is detected with a signal-to-noise 50 at both frequencies. We combine the 150 and 220 GHz data to remove the majority of the point source power, and use the point source subtracted spectrum to detect Sunyaev-Zel'dovich (SZ) power at 2.6 σ. At = 3000, the SZ power in the subtracted bandpowers is 4.2 ± 1.5 µK 2 , which is significantly lower than the power predicted by a fiducial model using WMAP5 cosmological parameters. This discrepancy may suggest that contemporary galaxy cluster models overestimate the thermal pressure of intracluster gas. Alternatively, this result can be interpreted as evidence for lower values of σ 8 . When combined with an estimate of the kinetic SZ contribution, the measured SZ amplitude shifts σ 8 from the primary CMB anisotropy derived constraint of 0.794 ± 0.028 down to 0.773 ± 0.025. The uncertainty in the constraint on σ 8 from this analysis is dominated by uncertainties in the theoretical modeling required to predict the amplitude of the SZ power spectrum for a given set of cosmological parameters.
A Measurement of the Angular Power Spectrum of the Anisotropy in the Cosmic Microwave Background
The Astrophysical Journal, 1997
We report on a measurement of the angular power spectrum of the anisotropy in the Cosmic Microwave Background. The anisotropy is measured in 23 different multipole bands from ℓ = 54 (≈ 3 • ) to ℓ = 404 (≈ 0.45 • ) and in 6 frequency bands from 26 GHz to 46 GHz over three observing seasons. The measurements are consistent from year to year. The frequency spectral index of the fluctuations (measured at low ℓ) is consistent with that of the CMB and inconsistent with either dust or Galactic free-free emission. Furthermore, the observations of the MSAM1-92 experiment ) are repeated and confirmed. The angular spectrum shows a distinct rise from δT ℓ ≡ ℓ(2ℓ + 1) < |a m ℓ | 2 > /4π = 49 +8 −5 µK at ℓ = 87 to δT ℓ = 85 +10 −8 µK at ℓ = 237. These values do not include an overall ±14% (1σ) calibration uncertainty. The analysis and possible systematic errors are discussed.
The Astrophysical Journal, 2003
We report measurements of anisotropy in the cosmic microwave background radiation over the multipole range ℓ ∼ 200 → 3500 with the Cosmic Background Imager based on deep observations of three fields. These results confirm the drop in power with increasing ℓ first reported in earlier measurements with this instrument, and extend the observations of this decline in power out to ℓ ∼ 2000. The decline in power is consistent with the predicted damping of primary anisotropies. At larger multipoles, ℓ = 2000-3500, the power is 3.1σ greater than standard models for intrinsic microwave background anisotropy in this multipole range, and 3.5σ greater than zero. This excess power is not consistent with expected levels of residual radio source contamination but, for σ 8 1, is consistent with predicted levels due to a secondary Sunyaev-Zeldovich anisotropy. Further observations are necessary to confirm the level of this excess and, if confirmed, determine its origin.
The anisotropy in the cosmic microwave background at degree angular scales
The Astrophysical Journal, 1995
We detect anisotropy in the cosmic microwave background (CMB) at degree angular scales and confirm a previous detection reported by . The root-mean-squared amplitude of the fluctuations is 44 +13 −7 µK. This may be expressed as the square root of the angular power spectrum in a band of multipoles between l ef f = 69 +29 −22 . We find δT l = l(2l + 1) < |a m l | 2 > /4π = 42 +12 −7 µK. The measured spectral index of the fluctuations is consistent with zero, the value expected for the CMB. The spectral index corresponding to Galactic free-free emission, the most likely foreground contaminant, is rejected at approximately 3σ.
The Astrophysical Journal, 2000
We present a map and an angular power spectrum of the anisotropy of the cosmic microwave background (CMB) from the first flight of MAXIMA. MAXIMA is a balloon-borne experiment with an array of 16 bolometric photometers operated at 100 mK. MAXIMA observed a 124 deg 2 region of the sky with 10 ′ resolution at frequencies of 150, 240 and 410 GHz. The data were calibrated using in-flight measurements of the CMB dipole anisotropy. A map of the CMB anisotropy was produced from three 150 and one 240 GHz photometer without need for foreground subtractions. Analysis of this CMB map yields a power spectrum for the CMB anisotropy over the range 36 ≤ ℓ ≤ 785. The spectrum shows a peak with an amplitude of 78 ± 6 µK at ℓ ≃ 220 and an amplitude varying between ∼ 40 µK and ∼ 50 µK for 400 ℓ 785. Subject headings: cosmic microwave background-cosmology: observations
The Astrophysical Journal, 2003
We analyze the Cosmic Microwave Background (CMB) anisotropy data from the independent COBE FIRAS and DMR observations. We extract the frequency spectrum of the FIRAS signal that has the spatial distribution seen by DMR and show that it is consistent with CMB temperature fluctuations in the radiation well into the Wien region of the spectrum. Conversely, we form a map of the Planckian component of the sky temperature from FIRAS and show that it correlates with the DMR anisotropy map. The rms fluctuations at angular scales of 7 • are 48±14 µK for the FIRAS data vs 35±2 µK for the DMR data and 31±6 µK for the combination (1 σ uncertainties). The consistency of these data, from very different instruments with very different observing strategies, provide compelling support for the interpretation that the signal seen by DMR is, in fact, temperature anisotropy of cosmological origin. The data also limit rms fluctuations in the Compton y parameter, observable via the Sunyaev-Zel'dovich effect, to ∆y < 3 × 10 −6 (95% CL) on 7 • angular scales.
A Measurement of Anisotropy in the Cosmic Microwave Background on 7′–22′ Scales
The Astrophysical Journal, 2000
We report a measurement of anisotropy in the cosmic microwave background radiation (CMBR) on 7 ′ − 22 ′ scales. Observations of 36 fields near the North Celestial Pole (NCP) were made at 31.7 and 14.5 GHz, using the 5.5-meter and 40-meter telescopes at the Owens Valley Radio Observatory (OVRO) from 1993 to 1996. Multi-epoch VLA observations at 8.5 and 15 GHz allow removal of discrete source contamination. After point-source subtraction, we detect significant 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 µm dust emission. Lack of Hα emission near the NCP suggests that this foreground is either high-temperature thermal bremsstrahlung (T e ∼ > 10 6 K), flat-spectrum synchrotron 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 β ≥ −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 fluctuation amplitude of 82 +12.1 −9.1 µK, including 4.3% calibration uncertainty and 12% sample variance (68% confidence). In terms of the angular power spectrum, C l = |a m l | 2 , averaged over a range of multipoles l = 361 − 756, the detected broadband amplitude is δT le ≡ [l(l + 1)C l /2π] 1/2 = 59 +8.6 −6.5 µK. This measurement, when combined with small angular-scale upper limits obtained at the OVRO, indicates that the CMBR angular power spectrum decreases between l ∼ 600 and l ∼ 2000 and is consistent with flat cosmological models. Subject headings: cosmic microwave background-cosmology: observations