Work

Fast partial-sky spherical harmonic transforms

Year: 2026

Type: article

Abstract: Context. Our main motivations are the South Pole Observatory program targeting primordial gravitational waves from inflation and cosmic microwave background (CMB) lensing from South Pole Telescope, requiring high-resolution, numerically intensive work on small sky fractions. Aims. We aim to make significant improvements in the efficiency of general-purpose spherical harmonic transforms on limited regions of the sky. Methods. We extended the doubled Fourier sphere (DFS) method, which allowed it to handle more efficiently high numbers of locations on a region of the sphere. Results. We achieved speed-up factors ranging from 3 to 10 on the SPT-3G main field, along with a BICEP3 deep footprint and much more on smaller patches, at the same level of accuracy. Conclusions. Our algorithm allowed us to eliminate the usual disadvantages of arbitrary pixelisations in comparison to isolatitude pixelisations (or flat-sky approximations), making it ideal for ambitious workflows that require repeated spherical harmonic transforms on limited sky regions.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202661409

Authors: J. Carron, M. Reinecke

Institutions: University of Geneva, University of Sussex, Università della Svizzera italiana, Max Planck Institute for Astrophysics

Language: English

Topic: Cosmology and Gravitation Theories

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $1,865

Funders: National Science Foundation, Science and Technology Facilities Council