30 GHz observations of sources in the VSA fields

TL;DR

This study measures the flux densities of extragalactic sources at 30 GHz in VSA fields, providing data crucial for understanding foreground contamination in cosmic microwave background studies.

Contribution

First measurement of source flux densities at 30 GHz in VSA fields, establishing source surface density and spectral index distribution relevant for CMB analysis.

Findings

Detected 57 sources above 5mJy at 30 GHz

Surface density of >10mJy sources is 2.0±0.4 per square degree

No evidence found for rising spectra sources at high frequencies

Abstract

Small angular scale (high l) studies of cosmic microwave background anisotropies require accurate knowledge of the statistical properties of extragalactic sources at cm-mm wavelengths. We have used a 30 GHz dual-beam receiver (OCRA-p) on the Torun 32-m telescope to measure the flux densities of 121 sources in VSA fields selected at 15 GHz with the Ryle Telescope. We have detected 57 sources above a limiting flux density of 5mJy, of which 31 sources have a flux density greater than 10mJy, which is our effective completeness limit. From these measurements we derive a surface density of sources above 10mJy at 30 GHz of 2.0+/-0.4 per square degree. This is consistent with the surface density obtained by Mason et al. (2009) who observed a large sample of sources selected at a much lower frequency (1.4 GHz). We have also investigated the dependence of the spectral index distribution on flux density by comparing our results with those for sources above 1 Jy selected from the WMAP 22 GHz catalogue. We conclude that the proportion of steep spectrum sources increases with decreasing flux density, qualitatively consistent with the predictions of deZotti et al. (2005). We find no evidence for an unexpected population of sources whose spectra rise towards high frequencies, which would affect our ability to interpret current high resolution CMB observations at 30 GHz and above.