Simulating a full-sky high resolution Galactic synchrotron spectral index map using neural networks

TL;DR

This paper develops a neural network-based model to generate high-resolution Galactic synchrotron spectral index maps, aiding in foreground removal for 21 cm cosmology experiments by providing realistic simulations of Galactic emission.

Contribution

The work introduces a convolutional neural network approach to produce high-resolution spectral index maps from lower-resolution data, improving the realism of Galactic foreground models for cosmological studies.

Findings

Neural network maps match observational data at 14.4 arcmin resolution.

Foreground removal effectiveness varies with spectral index model resolution.

No resolution finer than 5 degrees is necessary for effective foreground subtraction.

Abstract

We present a model for the full-sky diffuse Galactic synchrotron spectral index with an appropriate level of spatial structure for a resolution of 56 arcmin (to match the resolution of the Haslam 408 MHz data). Observational data at 408 MHz and 23 GHz have been used to provide spectral indices at a resolution of 5 degrees. In this work we make use of convolutional neural networks to provide a realistic proxy for the higher resolution information, in place of the genuine structure. Our deep learning algorithm has been trained using 14.4 arcmin observational data from the 1.4 GHz Parkes radio continuum survey. We compare synchrotron emission maps constructed by extrapolating the Haslam data using various spectral index maps, of different angular resolution, with the Global Sky Model. We add these foreground maps to a total emission model for a 21 cm intensity mapping experiment, then attempt to remove the foregrounds. The different models all display different spectral or spatial behaviour and so each provide a useful and different tool to the community for testing component separation techniques. We find that for an experiment operating using a cosine aperture taper beam with a primary Full Width at Half Maximum between 1.1 and 1.6 degrees, and the principal component analysis technique of foreground removal, there is a discernible difference between synchrotron spectral index models with a resolution larger than 5 degrees but that no greater resolution than 5 degrees is required.