Stephen Hancock

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 declination +35°. These experiments are sensitive to multipoles in the range l = 10-30. The sensitivities per beam are 56 and 20 μK for the 10 and 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 ΔTrms ~ 32 μK. In the case of a Harrison-Zeldovich spectrum for the primordial fluctuations, a likelihood analysis shows that this signal corresponds to a quadrupole amplitude Qrms-PS = 20.1+ 7.1−5.4 μK, in agreement with our previous results at declination +40° and with the results of the COBE DMR. There is clear evidence for the presence of individual features in the right ascension range 190°-250° with a peak-to-peak amplitude of ~110 μK. 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.

Comparison of the COBE DMR and Tenerife Data

We have compared the Tenerife data with the COBEDifferential Microwave Radiometer (DMR) 2 year data in the declination+40 region of the sky observed by the Tenerife experiment. Using theGalactic plane signal at 30 GHz, we show that the two data sets arecross-calibrated to within 5 percent. The high Galactic latitude datawere investigated for the presence of common structures with theproperties of cosmic microwave background (CMB) fluctuations. The mostprominent feature in the Tenerife data (AT 80 muK) appears to be presentin both the 53 and 90 GHz DMR maps and has the Planckian spectrumexpected for CMB anisotropy. The cross-correlation function of theTenerife and DMR scans is indicative of common structure and at zero laghas the value C(0)112=34+1153 muK. The combination of the spatial andspectral information from the two data sets is consistent with thepresence of cosmic microwave background anisotropies common to both. Theprobability that noise could produce the observed agreement is less than5 percent.

Detections of Primary and Secondary Anisotropies in the CMB

The current state of both primordial and secondary cosmic microwave background (CMB) anisotropy measurements is reviewed, with particular emphasis on the three CMB programmes currently underway at MRAO Cambridge. Results are presented from the Tenerife experiments observing on ~ 5° scales at frequencies of 10, 15 and 33 GHz. The best scan attains a sensitivity ~20μK and clear features are present with the properties expected for CMB anisotropy. On smaller scales ~ 0.5°, the Cosmic Anisotropy Telescope has been used to map a 2° x 2° field of the the sky at a frequency of 13.5 GHz. Details of the instrument are given along with preliminary sensitivity results. Observations of cluster Abell 2218 with the Ryle Telescope are described and used in conjunction with X-ray maps from the ROSAT and Einstein satellites to place a limit on the Hubble constant of \( {H_o} = 43_{ - 22}^{ + 33}\;km\;{s^{ - 1}}\;Mp{\user2{c}^{}} \). The implications of these observations are discussed in the context of continued CMB observations from ground-based sites and plans are presented for the Very Small Array.