The Parkes Galactic Meridian Survey: observations and CMB polarization foreground analysis

Abstract

We present observations and cosmic microwave background (CMB) foreground analysis of the Parkes Galactic Meridian Survey, an investigation of the Galactic latitude behaviour of the polarized synchrotron emission at 2.3 GHz with the Parkes Radio Telescope. The survey consists of a 5◦ wide strip along the Galactic meridian l = 254◦ extending from the Galactic plane to the South Galactic pole. We identify three zones distinguished by polarized emission properties: the disc, the halo and a transition region connecting them. The halo section lies at latitudes |b| > 40◦ and has weak and smooth polarized emission mostly at large scale with steep angular power spectra of median slope βmed ∼ −2.6. The disc region covers the latitudes |b| < 20◦ and has a brighter, more complex emission dominated by the small scales with flatter spectra of median slope βmed = −1.8. The transition region has steep spectra as in the halo, but the emission increases towards the Galactic plane from halo to disc levels. The change of slope and emission structure at b ∼ −20◦ is sudden, indicating a sharp disc–halo transition. The whole halo section is just one environment extended over 50◦ with very low emission which, once scaled to 70 GHz, is equivalent to the CMB B-mode emission for a tensor-toscalar perturbation power ratio rhalo = (3.3 ± 0.4) × 10−3. Applying a conservative cleaning procedure, we estimate an r detection limit of δr ∼ 2 × 10−3 at 70 GHz (3σ confidence limit) and, assuming a dust polarization fraction of <12 per cent, δr ∼ 1 × 10−2 at 150 GHz. The 150-GHz limit matches the goals of planned sub-orbital experiments, which can therefore be conducted at this high frequency. The 70-GHz limit is close to the goal of proposed next-generation space missions, which thus might not strictly require space-based platforms