Measurements of the diffuse Galactic synchrotron spectral index and curvature from MeerKLASS pilot data

TL;DR

This study uses MeerKAT pilot data to measure the spectral index and curvature of diffuse Galactic synchrotron emission below 1 GHz, confirming calibration accuracy and supporting future interstellar medium research.

Contribution

First measurement of synchrotron spectral index and curvature using MeerKAT data in the 100 MHz to 1 GHz range, aligning with previous experiments and validating calibration methods.

Findings

Spectral index between -2.75 and -2.71 from 45 to 1055 MHz.

Spectral curvature with β = -2.55 ± 0.13 and c = -0.12 ± 0.05.

Results consistent with ARCADE2 and EDGES measurements.

Abstract

21cm intensity mapping experiments are bringing an influx of high spectral resolution observational data in the $\sim100$ MHz $- 1$ GHz regime. We use pilot $971-1075$ MHz data from MeerKAT in single-dish mode, recently used to test the calibration and data reduction scheme of the upcoming MeerKLASS survey, to probe the spectral index of diffuse synchrotron emission below 1 GHz within $145^{\circ} < \alpha < 180^{\circ}$, $-1^{\circ} < \delta < 8^{\circ}$. Through comparisons with data from the OVRO Long Wavelength Array and the Maipu and MU surveys, we find an average spectral index of $-2.75 < \beta < -2.71$ between 45 and 1055 MHz. By fitting for spectral curvature with a spectral index of the form $\beta + c \, {\rm{ln}}(\nu / 73~{\rm MHz})$, we measure $\beta = -2.55 \pm 0.13$ and $c = -0.12 \pm 0.05$ within our target field. Our results are in good agreement (within $1\sigma$) with existing measurements from experiments such as ARCADE2 and EDGES. These results show the calibration accuracy of current data and demonstrate that MeerKLASS will also be capable of achieving a secondary science goal of probing the interstellar medium.