Observation of Cosmic Microwave Background Structure with the Tenerife Experiments

131 Observation of Cosmic Microwave Background Structure with the Tenerife Experiments C. M. Gutierrez1 1 Instituto de Astroj{sica de Canarias, 38200 La Laguna, Te nerife, SPA IN. Abstract The Tenerife Cosmic Microwave Background ( CMB) experiments are mapping a region of 5000 square degrees on the sky. Several beam-switching radiometers at frequencies of 10, 15 and 33 GHz have been operating at the Teide Observatory (Tenerife) for more than ten years. Here we present the current observational status of the experiments, with special attention to the data at Dec.=+35°. In this strip, the data at 15 GHz have a signal to noise ratio � 2 and show clear evidence for the presence of individual features at high Galactic latitude. Assuming a Harrison-Zel'dovich spectrum for the primordial fluctuations, a likelihood analysis of this data at 15 GHz shows the presence of a signal with amplitude = 20! in agreement with our previous results at Dec.=+40° and with QRMS-PS � µK, the results of COBE DMR. From the results at 10 GHz we conclude that the possible difuse Galactic contamination at 15 GHz should be :'.'.: 25 % of the detected signal. 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 invariance in amplitude along such a large range in frequency (10 - 90 GHz) is strongly indicative of an intrinsic cosmological origin for such structures. Introduction 1 The study of the CMB has progressed decisively in recent years, with the detection of the fluctuationsby the COBE DMR instrument [1, 11], the direct observation of features [5] and the statistical detections of signals on angular scales larger than a few minutes (see [6] for a summary of the observational status). The current observations constrain the CMB power spectrum to multipoles � 700, allowing the overall level of normalization to be determined and presenting good evidence of the existence of the Doppler peak predicted by standard inflationaryscenarios. 132 Nevertheless, a determination in detail of the CMB spectrum will require more observations, extending the angular range, the region observed and the spectral range. The Tenerife CMB experiments are a collaboration between the University of Manchester, the IAC Tenerife and MRAO Cambridge. The instruments consist of three independent two channel receivers, operating at 10, 15 and 33 GHz, installed at the "Observatorio de! Teide" on the island of Tenerife (Spain). The three instruments operate using a double-difference technique, with a beam response of the form -0.5, +l, -0.5, with three beams (FWHM� 5°): the positive in the meridian and the other two displaced 8�1 in declination. The three instruments use high electron mobility transistor (HEMT) amplifiers with resulting theoretical sensitivities, including both channels, of 5.6, 3.4 and 2.2 mK Hz-1/2 at 10, 15 and 33 GHz respectively. We observe strips of the sky separated by 2�5 coveringx declinations 30° to 45°. Our objective is to obtain a map in this band, with sensitivities of 50 µK at 10 GHz, and 20 µK at 15 and 33 GHz. Table 1 shows the current sensitivity of our observations in the region RA=l60°-250°. CMB fluctuations with an amplitude of QRMS-PS � 20 µK should produce an rms in our scans � 30 µK. With the sensitivity achieved, we can use the data at 10 GHz to constrain the Galactic contribution at higher frequencies, whilst at 15 GHz it is possible to detect and map directly CMB features. At 33 GHz a large fraction of data are rejected due to atmospheric contamination, and only the data at Dec.=+40° have similar sensitivities to those at 15 GHz. Table 1: Standard error (in µK) per beam sized area. Dec. (deg.) 10 GHz 15 GHz 33 GHz 30.0 20 32.5 54 24 42 35.0 56 20 33 37.5 41 19 33 40.0 44 19 21 42.5 63 22 50 45.0 80 26 Figure 1 shows the stacked scans at 15 GHz. The highest intensity in these scans lies in the Galactic plane crossings at RA�300°-310° and shows the typical triple beam response of our instruments. The weak crossings are at RA�60°-90°. Comparing the amplitudes of such crossings at 10, 15 and 33 GHz we have demonstrated that the main source of signal in the Galactic plane at these frequencies is free-free emission with spectral index � 2. The search for intrinsic CMB structure (see next section) has been conducted at high Galactic latitude in the RA range 160° to 250°, where no structures are seen on this intensity scale. 2 Data at high Galactic latitude The contribution due to known point-sources has been calculated using the Kuhr catalogue [9], the VLA calibrators, and the Michigan and Metsahovi monitoring programme. In the ban:d of the sky observed by our instruments the more intense radio-sources at high Galactic latitude are 3C345, 0923+379 and 3C286. All these sources have been detected in our scans, 133 45.o· 42.5. � 40.0" 37_5• "' E C> "' 35.0" �--A--- I 32.5" 30.0" o· 100· 200· RA (degrees} Figure 1: Stacked scans at 15 GHz showing the strong (RA� 300° - 310°) and the weak (RA � 60° - 90°) crossings of the Galactic plane. 100 0 -100 ! 160 180 200(degrees) 220 240 RA 100 0 -100 160 180 200(degrees) 220 240 RA Figure 2: Section of data at high Galactic latitude in the band at Dec.=+35°. a/ 15 GHz and bf 10 GHz. 134 with the expected amplitudes and shapes. The contamination by a foreground of unresolved radio-sources is expected to have an rms ;S 30 µK, ;S 15 µK and ;S 3 µK at 10, 15 and 33 GHz respectively [4]. We have demonstrated [3] the unreliability of the predictions of the difuse Galactic foreground using the low frequencies surveys at 408 [7] and 1420 MHz [10]. Nevertheless, it is possible to infer such a contribution in our data from a comparison between our own measurements at 10 and 15 GHz and the COBE DMR results at 31, 53 and 90 GHz (see below). After subtraction of the known point-source contribution, we have applied a likelihood analysis [5] to the data at 10 GHz and 15 GHz (the analysis of the data at 33 GHz is in progress). We selected the section of the data at RA=160° - 250° and assume a Harrison Zel'dovich spectrum for the primordial fluctuations. A summary of the results is given in Table 2. Upper limits and detections are quoted at 95 % C.L. and 68 % C.L. respectively. The results in all strips at 15 GHz are consistent with a CMB signal QRMS-PS � 20 µK, whilst at 10 GHz the data are in some cases not sensitive enough to detect CMB signals and seem to have some degree of Galactic contamination. The results at 15 GHz correspond to values only sligthly larger than the level of the signal present in the COBE DMR data (QRMS-PS = 18± 1.5 µK, [1]) and indicate that most of the signal observed in our data at 15 GHz is intrinsic CMB structure. At 10 GHz a foreground-contamination � 2 times higher than at 15 GHz is expected. For instance comparing the likelihood results of the 15 GHz data at Dec.=+35° with the COBE DMR normalization, we estimate that the foreground contamination would contribute with 8 !'i.TRMS ::; µK at 15 GHz. This value is in agreement with the strong limits placed by the 10 GHz data and implies that even at 10 GHz more than half of the signals are due to CMB fluctuations. Table 2: Results of the likelihood analysis (expected QRMS-PS in µK) for data over RA=160°- 2500. Dec. (deg.) 10 GHz 15 GHz 30.0 22:��0 32.5 33:1:1� 25:1:1i 35.0 ::; 33 20:1:� :1: 37.5 35 1� 19:1:� 40.0 ::; 31 23:1:�1 42.5 ::; 44 29!i� 45.0 59:1:i� 21:1:1� Comparison with COBE DMR data 3 A Wiener filter, assuming a CDM model, was applied [2] to the two-year COBE DMR data at 53 and 90 GHz. From this filtered map the prediction for the Tenerife experiment was computed over the region 35° ::;Dec.::; 45°. At high Galactic latitude, the most significant features predicted in the Tenerife data are two hot spots with peak amplitudes � 50 - 100 µK around Dec.=+35°, at RA� 220° and � 250°. A comparison between the reconvolved results of our data using Maximum Entropy [8] and this prediction is plotted in Fig. 3. At 15 135 100 50 :;;: , 3 ,,\ ....; I I '= 0 I "" I \ , c.i ·.. " , "' -50 -100 160 180 200 220 240 RA (degrees) Figure 3: Comparison between COBE DMR and Tenerife at Dec.=+35°. Solid and dashed lines correspond to the Tenerife data at 15 and 10 GHz respectively; dotted are the COBE DMR predictions. GHz the two most intense structures agree in amplitude and position whith the predicted ones, with only slight shift in position for the feature at RA�250°; this structure is also detected a in the 10 GHz results. The 10 and 15 GHz data also show a possible third positive feature at RA� 180° with little evidence of this in the prediction. The global agreement between our data and COBE DMR predictions strongly suggests that the main structures detected at Dec.=+35° are cosmological in origin. 4 Future programme Data collection with the radiometers will continue in order to give a coverage of Dec.=+30° to 45° at the full sampling separation of 2°5 (half the FWHM).

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