We present a determination of the cosmic microwave background dipole amplitude and direction from the COBE Di erential Microwave Radiometers (DMR) rst year of data. Data from the six DMR channels are consistent with a Dopplershifted Planck function of dipole amplitude T = 3:365 0:027 mK toward direction (l II ; b II ) = (264:4 0:3 ; 48:4 0:5 ). The implied velocity of the Local Group with respect to the CMB rest frame isṽ LG = 627 22 km s 1 toward (l II ; b II ) = (276 3 ; 30 3 ). DMR has also mapped the dipole anisotropy resulting from the Earth's orbital motion about the Solar system barycenter, yielding a measurement of the monopole CMB temperature T 0 at 31.5, 53, and 90 GHz, T 0 = 2:75 0:05 K. Subject headings: cosmic microwave background | cosmology: observations 2
The rst two years of COBE Di erential Microwave Radiometers (DMR) observations of the cosmic microwave background (CMB) anisotropy are analyzed and compared with our previously published rst year results. The results are consistent, but the addition of the second year of data increases the precision and accuracy of the detected CMB temperature uctuations. The two-year 53 GHz data are characterized by RMS temperature uctuations of ( T) rms (7 ) = 44 7 K and ( T) rms (10 ) = 30:5 2:7 K at 7 and 10 angular resolution respectively. The 53 90 GHz cross-correlation amplitude at zero lag is C(0) 1=2 = 36 5 K (68% CL) for the unsmoothed (7 resolution) DMR data.A likelihood analysis of the cross correlation function, including the quadrupole anisotropy, gives a most likely quadrupole-normalized amplitude, Q rms PS , of 12:4 +5:2 3:3 K (68% CL) and a spectral index n = 1:59 +0:49 0:55 (68% CL) for a power law model of initial density uctuations, P(k) / k n . With n xed to 1.0 the most likely amplitude is 17:4 1:5 K (68% CL). Excluding the quadrupole anisotropy we nd Q rms PS = 16:0 +7:5 5:2 K (68% CL), n = 1:21 +0:60 0:55 (68% CL), and, with n xed to 1.0 the most likely amplitude is 18:2 1:6 K (68% CL). Monte Carlo simulations indicate that these derived estimates of n may be biased by +0:3 (with the observed low value of the quadrupole included in the analysis) and +0:1 (with the quadrupole excluded). Thus the most likely bias-corrected estimate of n is between 1.1 and 1.3. Our best estimate of the dipole from the two-year DMR data is 3:363 0:024 mK towards Galactic coordinates (`; b) = (264:4 0:2 ; +48:1 0:4 ), and our best estimate of the RMS quadrupole amplitude in our sky is 6 3 K (68% CL).Subject headings: cosmology: cosmic microwave background -large scale structure of the universe -observations { 3 {
We have searched the temperature maps from the COBE Di erential Microwave Radiometers (DMR) rst two years of data for evidence of unresolved sources. The high-latitude sky (jbj > 30 ) contains no sources brighter than 192 K thermodynamic temperature (322 Jy at 53 GHz). The cumulative count of sources brighter than threshold T , N (>T ), is consistent with a superposition of instrument noise plus a scale-invariant spectrum of cosmic temperature uctuations normalized to Q rms PS = 17 K. We examine the temperature maps toward nearby clusters and nd no evidence for any Sunyaev-Zel'dovich e ect, y < 7.3 10 6 (95% CL) averaged over the DMR beam. We examine the temperature maps near the brightest expected radio sources and detect no evidence of signi cant emission. The lack of bright unresolved sources in the DMR maps, taken with anisotropy measurements on smaller angular scales, places a weak constraint on the integral number density of any unresolved Planck-spectrum sources brighter than ux density S, n(>S) < 2 10 4 (S=1 Jy) 2 sr 1 .Subject headings: cosmic microwave background | radio continuum:general 2
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