All-sky Galactic radiation at 45 MHz and spectral index between 45 and 408 MHz

TL;DR

This study creates all-sky maps of Galactic synchrotron emission at 45 MHz and the spectral index between 45 and 408 MHz, revealing spatial variations influenced by absorption and Galactic structures.

Contribution

It provides the first reliable all-sky spectral index map at low frequencies, combining observations and existing data with corrections for offsets and extragalactic contributions.

Findings

Spectral index varies between 2.1 and 2.7 across the sky.

Lower spectral index values (<2.5) occur at low Galactic latitudes due to free-free absorption.

Maximum spectral index observed near the Northern Spur.

Abstract

Aims: We study the Galactic large-scale synchrotron emission by generating a reliable all-sky spectral index map and temperature map at 45 MHz. Methods: We use our observations, the published all-sky map at 408 MHz, and a bibliographical compilation to produce a map corrected for zero-level offset and extragalactic contribution. Results: We present full sky maps of the Galactic emission at 45 MHz and the Galactic spectral index between 45 and 408 MHz with an angular resolution of 5\degs. The spectral index varies between 2.1 and 2.7, reaching values below 2.5 at low latitude because of thermal free-free absorption and its maximum in the zone next to the Northern Spur.