Limits to cosmic background radiation fluctuations at 8.44 GHz between angular scales 10″ and 200″

Edward B. Fomalont, R. Bruce Partridge, James D. Lowenthal, Rogier Windhorst

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43 Scopus citations


We have used the VLA at 8.44 GHz to measure fluctuations in the cosmic background radiation (CBR) from two deep images, each 7′ x 7′ in size. No fluctuations between the angular scales 10″ and 200″ were detected. The most accurate limit (95% confidence) is ΔT/TCBR < 1.9 x 10-5 for 80″ resolution. For random Gaussian fluctuations with coherence angle θc, the limits are ΔT/TCBR < 30 x 10-5 for 22″ < θc < 60″. Outside this range the limits increase to ΔT/TCBR < 5 x 10-5 at θc = 12″ or 100″ and ΔT/TCBR < 10 x 10-5 at θc = 5″ or 120″. Similar limits have been obtained for the circularly and linearly polarized components of the CBR fluctuations. These limits were derived from the residual fluctuations in the images after (1) removing brighter foreground sources (> 14.5 μJy) which covered about 10% of each image; (2) estimating fluctuations of weaker sources by extrapolating the count of dN/dS = 4.6S-2.3 Jy-1 sr-1 to 4 μJy; and (3) determining fluctuations from receiver noise and instrumental errors by comparing the image variances from two independent halves of the data set. All analysis was made on dirty images, in which the statistical properties of instrumental and sky fluctuations are well-defined.

Original languageEnglish (US)
Pages (from-to)8-20
Number of pages13
JournalAstrophysical Journal
Issue number1
StatePublished - Feb 10 1993


  • Cosmic microwave background
  • Polarization

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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