arXiv subjects

C. M. Gutierrez

Publications and source records attributed to C. M. Gutierrez.

57 records · Page 4Linked to original sources

arXiv1997

Studies of CMB structure at Dec=40. II: Analysis and cosmological interpretation

We present a detailed analysis of the cosmic microwave background structure in the Tenerife Dec=+40 degrees data. The effect of local atmospheric contributions on the derived fluctuation amplitude is considered, resulting in an improved separation of the intrinsic CMB signal from noise. Our analysis demonstrates the existence of common structure in independent data scans at 15 and 33 GHz. For the case of fluctuations described by a Gaussian auto-correlation function, a likelihood analysis of our combined results at 15 and 33 GHz implies an intrinsic rms fluctuation level of 48^{+21}_{-15} uK on a coherence scale of 4 degrees; the equivalent analysis for a Harrison-Zel'dovitch model gives a power spectrum normalisation of Q_{rms-ps} = 22^{+10}_{-6} uK. The fluctuation amplitude is seen to be consistent at the 68% confidence level with that reported for the COBE two-year data for primordial fluctuations described by a power law model with a spectral index in the range 1.0 \le n \le 1.6. This limit favours the large scale CMB anisotropy being dominated by scalar fluctuations rather than tensor modes from a gravitational wave background. The large scale Tenerife and COBE results are considered in conjunction with observational results from medium scale experiments in order to place improved limits on the fluctuation spectral index; we find n=1.10 +/- 0.10 assuming standard CDM with H_{0}=50 kms^{-1}Mpc^{-1}.

astro-ph↗

arXiv1997

The estimation of the noise in cosmic microwave background anisotropy experiments

Even the most sensitive cosmic microwave background anisotropy experiments have signal to noise ratios <=5, so that an accurate determination of the properties of the cosmological signal requires a careful assessment of the experimental noise. Most of the experiments combine simultaneous multi-channel observations in which the presence of correlated noise is likely. This case is common for ground-based experiments in which an important fraction of the noise could be atmospheric in origin. Here, the way to compute and determine the effects produced by this correlated noise is discussed; in particular, the paper considers the Tenerife experiments (three radiometers at 10, 15 and 33 GHz with two independent receivers each) showing how this effect has been taking into account properly in the more recent analysis of these data. It will be demonstrated that for each of the three radiometers of these experiments, the atmospheric noise is equivalent to a Gaussian noise common to both channels with a coherence time smaller than the binning time, the net effect being an enhancement of the error-bars in the stacked scan as compared with the estimation for the case of pure uncorrelated noise. As expected from the spectral index of the atmosphere, the effect is more important at higher frequencies. The formalism is generalized and applied to the general case of simultaneous multi-channel observations.

astro-ph↗

arXiv1997

New Cosmological Structures on Medium Angular Scales Detected with the Tenerife Experiments

We present observations at 10 and 15 GHz taken with the Tenerife experiments in a band of the sky at Dec.=+35 degrees. These experiments are sensitive to multipoles in the range l=10-30. The sensitivity per beam is 56 and 20 microK for the 10 and the 15 GHz data, respectively. After subtraction of the prediction of known radio-sources, the analysis of the data at 15 GHz at high Galactic latitude shows the presence of a signal with amplitude Delta Trms ~ 32 microK. In the case of a Harrison-Zeldovich spectrum for the primordial fluctuations, a likelihood analysis shows that this signal corresponds to a quadrupole amplitude Q_rms-ps=20.1+7.1-5.4 microK, in agreement with our previous results at Dec.+=40 degrees and with the results of the COBE DMR. There is clear evidence for the presence of individual features in the RA range 190 degrees to 250 degrees with a peak to peak amplitude of ~110 microK. A preliminary comparison between our results and COBE DMR predictions for the Tenerife experiments clearly indicates the presence of individual features common to both. The constancy in amplitude over such a large range in frequency (10-90 GHz) is strongly indicative of an intrinsic cosmological origin for these structures.

astro-ph↗