The talk concerns L-BASS a new radio telescope designed to measure the diffuse radio sky at ~21 cm wavelength (L-Band) with unprecedented accuracy. We have two scientific “targets”:
1) The ARCADE team claim to have identified a new isotropic radio background which is distinct from the CMBR. However their interpretation depends upon decades-old low-frequency sky surveys whose absolute temperature calibration is uncertain. The jury is still out with three verdicts remaining possible:
• imperfections in the data are such that there is no background, other than that provided by the integrated emission from extragalactic radio sources;
• there is a background but it is primarily associated with the Milky Way; this would challenge the picture of our Galaxy as a typical spiral;
• there is a background and it is primarily extragalactic; since its origin is unknown this would be the most interesting photon field in sky.
2) The discovery of the CMBR (made with a ground-based instrument) highlighted the value of absolute brightness temperature measurement. Absolute temperature maps made with spacecraft have established the detailed properties of the CMBR but the analysis of these maps also depends on the lower frequency maps for accurate removal of the diffuse "foreground" emission from the Milky Way. These maps were mainly made with dish-type radio telescopes located in different hemispheres, and they suffer from significant (of order 1K or more) zero-level offsets and position-dependent calibration errors dominated by ground pick-up.
With L-BASS we aim to produce an absolutely calibrated map of the sky at L-band with an angular resolution of ∼20 degrees and a radiometric accuracy of ≤0.1K. This will be the most accurate all-sky map made with a ground-based instrument and will greatly improve our knowledge of the diffuse radio sky and should contribute to its interpretation.