Clustering at 74 MHz

TL;DR

This paper measures the angular clustering of radio sources at 74 MHz using VLSS data, providing the first such measurement at frequencies relevant to 21 cm cosmology, and finds a consistent power-law behavior.

Contribution

It presents the first measurement of radio source clustering at low frequencies relevant to 21 cm experiments, using VLSS data and fitting a power-law model.

Findings

Clustering follows a power-law with slope -1.2.

Amplitude of clustering is between 0.2 and 0.6 degrees.

Clustering amplitude is independent of flux threshold.

Abstract

In order to construct accurate point sources simulations at the frequencies relevant to 21 cm experiments, the angular correlation of radio sources must be taken into account. Using the 74 MHz VLSS survey, we measured the angular 2-point correlation function, w(\theta). We obtain the first measurement of clustering at the low frequencies relevant to 21 cm tomography. We find that a single power law with shape w(\theta) = A \theta^{-\gamma} fits well the data. For a galactic cut of 10 degrees, with a data cut of \delta less than -10 degrees, and a flux limit of S = 770 mJy, we obtain a slope of \gamma = (-1.2 +/- 0.35). This value of \gamma is consistent with that measured from other radio catalogues at the millimeter wavelengths. The amplitude of clustering has a length of 0.2 degrees - 0.6 degrees, and it is independent of the flux-density threshold.