Absolute Calibration of the Radio Astronomy Flux Density Scale at 22 to 43 GHz Using Planck

TL;DR

This paper establishes an absolute flux density calibration for ground-based radio telescopes at 22 to 43 GHz by using Planck satellite measurements, achieving 1-2% accuracy despite source variability.

Contribution

It introduces a method to transfer Planck's absolute calibration to ground-based radio telescopes at high frequencies, improving calibration accuracy.

Findings

Flux density scales are consistent within 1-2% accuracy.

VLA scale is 3.6% below Planck at 28 GHz.

Discrepancy increases to 6.2% at 43 GHz.

Abstract

The Planck mission detected thousands of extragalactic radio sources at frequencies from 28 to 857 GHz. Planck's calibration is absolute (in the sense that it is based on the satellite's annual motion around the Sun and the temperature of the cosmic microwave background), and its beams are well characterized at sub-percent levels. Thus Planck's flux density measurements of compact sources are absolute in the same sense. We have made coordinated VLA and ATCA observations of 65 strong, unresolved Planck sources in order to transfer Planck's calibration to ground-based instruments at 22, 28, and 43 GHz. The results are compared to microwave flux density scales currently based on planetary observations. Despite the scatter introduced by the variability of many of the sources, the flux density scales are determined to 1-2% accuracy. At 28 GHz, the flux density scale used by the VLA runs 3.6% +- 1.0% below Planck values; at 43 GHz, the discrepancy increases to 6.2% +- 1.4% for both ATCA and the VLA.