The prospects of measuring the angular power spectrum of the diffuse Galactic synchrotron emission with SKA1 Low

TL;DR

This paper discusses the potential of SKA1 Low to measure the angular power spectrum of the diffuse Galactic synchrotron emission, which is crucial for cosmological 21-cm studies and understanding the interstellar medium.

Contribution

It introduces the Tapered Gridded Estimator (TGE) for efficiently measuring the angular power spectrum from radio interferometric data and predicts its application with SKA1 Low for larger angular scales.

Findings

TGE is computationally efficient and avoids noise bias.

SKA1 Low can measure the DGSE power spectrum up to l ~ 10^5.

Higher sensitivity allows for better point source subtraction.

Abstract

The diffuse Galactic synchrotron emission (DGSE) is the most important diffuse foreground component for future cosmological 21-cm observations. The DGSE is also an important probe of the cosmic ray electron and magnetic field distributions in the turbulent interstellar medium (ISM) of our Galaxy. In this paper we briefly review the Tapered Gridded Estimator (TGE) which can be used to quantify the angular power spectrum of the sky signal directly from the visibilities measured in radio-interferometric observations. The salient features of the TGE are (1.) it deals with the gridded data which makes it computationally very fast (2.) it avoids a positive noise bias which normally arises from the system noise inherent to the visibility data, and (3.) it allows us to taper the sky response and thereby suppresses the contribution from unsubtracted point sources in the outer parts and the sidelobes of the antenna beam pattern. We also summarize earlier work where the TGE was used to measure the C_l of the DGSE using 150 MHz GMRT data. Earlier measurements of the angular power spectrum are restricted to smaller angular multipole l ~ 10^3 for the DGSE, the signal at the larger l values is dominated by the residual point sources after source subtraction. The higher sensitivity of the upcoming SKA1 Low will allow the point sources to be subtracted to a fainter level than possible with existing telescopes. We predict that it will be possible to measure the angular power spectrum of the DGSE to larger values of l with SKA1 Low. Our results show that it should be possible to achieve l_{max} ~ 10^4 and ~ 10^5 with 2 minutes and 10 hours of observations respectively.