From BEYONDPLANCK to COSMOGLOBE: Preliminary WMAP Q-band analysis

Abstract

We present the first application of the Cosmoglobe analysis framework by analyzing nine-year WMAP time-ordered observations that uses similar machinery to that of BeyondPlanck for the Planck Low Frequency Instrument (LFI). We analyzed only the Q-band (41 GHz) data and report on the low-level analysis process based on uncalibrated time-ordered data to calibrated maps. Most of the existing BeyondPlanck pipeline may be reused for WMAP analysis with minimal changes to the existing codebase. The main modification is the implementation of the same preconditioned biconjugate gradient mapmaker used by the WMAP team. Producing a single WMAP Q1-band sample requires 22 CPU-hrs, which is slightly more than the cost of a Planck 44 GHz sample of 17 CPU-hrs; this demonstrates that a full end-to-end Bayesian processing of the WMAP data is computationally feasible. In general, our recovered maps are very similar to the maps released by the WMAP team, although with two notable differences. In terms of temperature, we find a ∼ 2 µK quadrupole difference that most likely is caused by different gain modeling, while in polarization we find a distinct 2.5 µK signal that has been previously referred to as poorly measured modes by the WMAP team. In the Cosmoglobe processing, this pattern arises from temperature-to-polarization leakage from the coupling between the CMB Solar dipole, transmission imbalance, and sidelobes. No traces of this pattern are found in either the frequency map or TOD residual map, suggesting that the current processing has succeeded in modeling these poorly measured modes within the assumed parametric model by using Planck information to break the sky-synchronous degeneracies inherent in the WMAP scanning strategy.

Beyondplanck

“…This strongly suggests that a future joint analysis of Planck and WMAP data in the time-domain will be able to constrain the WMAP transmission imbalance parameters to a high accuracy. This work has already started, as discussed by Watts et al (2023).…”

“…Once that happens, the corresponding spatial modes will no longer need to be algebraically projected out, as is effectively done now; however, they may rather be used for scientific inference in the future, on the same footing as any other mode. This work has already started and preliminary results are discussed by Watts et al (2023).…”

“…The W-band channel is omitted because it is known to be contaminated by systematic residuals; seeBennett et al (2013),Watts et al (2023) for details. 4 http://healpix.jpl.nasa.gov A14, page 5 of 18Svalheim, T. L., et al: A&A 675, A14 (2023) …”

Beyondplanck

“…The differences that we see in the maps, however, indicate that this process is not perfect, as some of the spurious signal still makes it to the final maps without a perfect sidelobe model. For a real-world example of these issues, we refer the interested reader to the ongoing BeyondPlanck re-analysis of the WMAP data, for which far sidelobe contamination appears to be a dominant problem (Watts et al 2023).…”

“…Sidelobe signals can produce many types of errors in CMB analysis pipelines and they represent a potent source of systematic contamination (e.g., Planck Collaboration III 2016; Watts et al 2023). In particular, as the sidelobe response functions often are broadly distributed, this contamination can confuse important signals such as the CMB solar and orbital dipoles that are used for calibration.…”