RMS Radio Source Contributions to the Microwave Sky

TL;DR

This paper investigates the contribution of unresolved radio and X-ray sources to microwave sky fluctuations observed by WMAP, providing estimates of their impact on the observed anisotropies across different frequency bands.

Contribution

It introduces a method to constrain microwave sky fluctuations using cross-correlations with radio and X-ray maps, offering new estimates of unresolved source contributions.

Findings

Lower limit of ~2 microKelvin for Q band fluctuations from radio and X-ray correlations

Estimated ~5 microKelvin rms fluctuations in Q band consistent with WMAP observations

Fluctuation spectrum follows a beta = -2.1 +- 0.4 frequency dependence

Abstract

Cross-correlations of the WMAP full sky K, Ka, Q, V, and W band maps with the 1.4 GHz NVSS source count map and the HEAO I A2 2-10 keV full sky X-ray flux map are used to constrain rms fluctuations due to unresolved microwave sources in the WMAP frequency range. In the Q band (40.7 GHz), a lower limit, taking account of only those fluctuations correlated with the 1.4 GHz radio source counts and X-ray flux, corresponds to an rms Rayleigh-Jeans temperature of ~ 2 microKelvin for a solid angle of one square degree. The correlated fluctuations at the other bands are consistent with a beta = -2.1 +- 0.4 frequency spectrum. Using the rms fluctuations of the X-ray flux and radio source counts, and the cross-correlation of these two quantities as a guide, the above lower limit leads to a plausible estimate of ~ 5 microKelvin for Q-band rms fluctuations in one square degree. This value is similar to that implied by the excess, small angular scale fluctuations observed in the Q band by WMAP, and is consistent with estimates made by extrapolating low-frquency source counts.