# The angular power spectrum measurement of the Galactic synchrotron emission in two fields of the TGSS survey

## TL;DR

This study measures the angular power spectrum of diffuse Galactic synchrotron emission in two TGSS fields, providing insights crucial for foreground removal in 21-cm cosmology and advancing understanding of Galactic radio emission.

## Contribution

It presents the first detailed measurement of the Galactic synchrotron angular power spectrum at arcminute scales in two specific sky fields using the TGE method.

## Key findings

- Diffuse synchrotron dominates the emission in the studied angular range.
- Power law fits describe the angular power spectrum with specific amplitude and slope.
- One field shows a lower amplitude compared to other sky regions, indicating regional variation.

## Abstract

Characterizing the diffuse Galactic synchrotron emission at arcminute angular scales is needed to reliably remove foregrounds in cosmological 21-cm measurements. The study of this emission is also interesting in its own right. Here, we quantify the fluctuations of the diffuse Galactic synchrotron emission using visibility data for two of the fields observed by the TIFR GMRT Sky Survey (TGSS). We have used the 2D Tapered Gridded Estimator (TGE) to estimate the angular power spectrum $(C_{\ell})$ from the visibilities. We find that the sky signal, after subtracting the point sources, is likely dominated by the diffuse Galactic synchrotron radiation across the angular multipole range $240 \le \ell \lesssim 500$. We present a power law fit, $C_{\ell}=A\times\big(\frac{1000}{l}\big)^{\beta}$, to the measured $C_{\ell}$ over this $\ell$ range. We find that $(A,\beta)$ have values $(356\pm109~{\rm mK^2},2.8\pm0.3)$ and $(54\pm26~{\rm mK^2},2.2\pm0.4)$ in the two fields. For the second field, however, there is indication of a significant residual point source contribution, and for this field we interpret the measured $C_{\ell}$ as an upper limit for the diffuse Galactic synchrotron emission. While in both fields the slopes are consistent with earlier measurements, the second field appears to have an amplitude which is considerably smaller compared to similar measurements in other parts of the sky.