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The CMB power spectrum out to l=1400 measured by the VSA

Keith Grainge, Pedro Carreira, Kieran Cleary, Rod D. Davies, Richard J. Davis, Clive Dickinson, Ricardo Genova-Santos, Carlos M. Gutierrez, Yaser A. Hafez, Michael P. Hobson, Michael E. Jones, Rudiger Kneissl, Katy Lancaster, Anthony Lasenby, J. P. Leahy, Klaus Maisinger, Guy G. Pooley, Rafael Rebolo, Jose Alberto Rubino-Martin, Pedro Sosa Molina, Carolina Odman, Ben Rusholme, Richard D. E. Saunders, Richard Savage, Paul F. Scott, Anze Slosar, Angela C. Taylor, David Titterington, Elizabeth Waldram, Robert A. Watson, Althea Wilkinson

TL;DR

This work reports the CMB power spectrum measured by the Very Small Array (VSA) using an extended configuration, combined with earlier compact-array data, to cover $160 \le \ell \le 1400$. The extended array provides higher angular resolution and sensitivity, enabling clear detection of the first three acoustic peaks and a fall-off at high $\ell$, with marginal evidence for a fourth peak. Through careful calibration with Jupiter, extensive point-source subtraction, and robust data-quality checks, the study delivers a consistent, multi-configuration spectrum that agrees with other CMB experiments. The analysis enhances constraints on peak amplitudes and positions, contributing to tighter cosmological parameter inferences and informing upcoming extensions of VSA observations toward higher $\ell$.

Abstract

We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles l = 160 - 1400. Such measurements at high l are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall off in power at high l and starts to constrain the position and height of a fourth peak.

The CMB power spectrum out to l=1400 measured by the VSA

TL;DR

This work reports the CMB power spectrum measured by the Very Small Array (VSA) using an extended configuration, combined with earlier compact-array data, to cover . The extended array provides higher angular resolution and sensitivity, enabling clear detection of the first three acoustic peaks and a fall-off at high , with marginal evidence for a fourth peak. Through careful calibration with Jupiter, extensive point-source subtraction, and robust data-quality checks, the study delivers a consistent, multi-configuration spectrum that agrees with other CMB experiments. The analysis enhances constraints on peak amplitudes and positions, contributing to tighter cosmological parameter inferences and informing upcoming extensions of VSA observations toward higher .

Abstract

We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles l = 160 - 1400. Such measurements at high l are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall off in power at high l and starts to constrain the position and height of a fourth peak.

Paper Structure

This paper contains 10 sections, 5 figures, 6 tables.

Table of Contents

  1. Introduction
  2. The VSA extended array
  3. Observations
  4. Field centres
  5. Data reduction
  6. Source subtraction
  7. Results
  8. Data checks
  9. Power spectrum
  10. Discussion & conclusions

Figures (5)

  • Figure 1: Mosaiced and source-subtracted maps for each of the VSA regions: left, VSA1; centre, VSA2; right, VSA3. In each case the greyscale runs from $-150$ to $150 \, \mu$K and the contour indicates the half-power response of the combined primary beam.
  • Figure 2: Comparison of the compact and extended array maps for the central part of the VSA1 field. Greyscale: Compact array map, with greyscale running from $-250$ to $250 \, \mu$K. The sensitivity is nearly uniform across this area. Contours: Extended array map, contour interval $30 \, \mu$K. The map has been corrected for the combined effect of the primary beams, so the noise level rises towards the edge of the map.
  • Figure 3: Window functions for the combined compact and extended array data set. The functions are normalised to unit area, and different bins are plotted with different linestyles.
  • Figure 4: Combined CMB power spectrum from the three mosaiced VSA fields. The error-bars represent $1\sigma$ limits; the two sets of data points correspond to alternative interleaved binnings of the data.
  • Figure 5: A comparison of the VSA data (filled circles) with results from the BOOMERANG (open squares), MAXIMA (open circles), DASI (open triangles) and CBI (stars) experiments. Two sets of error bars are plotted for each data set; the smaller (inner) of the two indicate only random errors, whilst the larger bars indicate the amount by which the inner points could move due to absolute calibration and beam uncertainty. In each case the error bars indicate $1\sigma$ limits.