Speaker
Description
Spherical harmonic functions are a natural set of basis functions for describing the brightness distribution of the celestial sphere. As the Earth rotates, the fringes projected on the sky by a zenith phased interferometer sample the celestial sphere. The resulting visibilities measured by a single baseline are therefore periodic over a sidereal day, and are Fourier conjugate with the spherical harmonic phase term m. By Fourier transforming the measured visibilities over a 24-hour transit observation, and with knowledge of the instrument (baseline fringes, beam pattern), we can solve for the real spherical harmonic coefficients of the sky. As a result, the m-mode transit interferometry technique precludes the need to mosiac images and naturally includes the widefield effects present for instruments such as MWA and LOFAR, without the need to perform w-projection or w-stacking. Therefore, this technique is well suited for making high quality all-sky maps, of the large-scale diffuse Galactic emission. Accurate maps of large-scale structures are paramount for Epoch of Reionisation science (a key SKA science goal), and are necessary for mitigation, calibration and removal of foreground contaminants. Therefore, all-sky maps are important not just for precursor instruments such as the MWA, but for the SKA-LOW. Current foreground models use the scaled and desourced version of the 408MHz Haslam map, which is suboptimal for the low frequency ranges of the cosmic dawn and EoR. In this work, we present an all-sky map at 160MHz with a resolution of ~40 arcminutes (comparable to the 408MHz Haslam map), covering the entire Southern Hemisphere to bridge this gap. This map was constructed by combining data from both the MWA and the EDA2 (an SKA-low prototype station), where the EDA2 samples large-scale diffuse structures, and the MWA samples finer small-scale angular structures. Future maps made with the SKA-LOW will greatly improve upon this work, by utilising the high sensitivity and baseline distribution of the SKA-LOW core. This will result in highly sensitive maps across a range of frequencies, and angular scales (arc minute scale), for the scientific community.
| Timeslot preferences | 15 minutes |
|---|
