Develop a proper treatment of the interferometric w-term

Develop a proper treatment of the w-term in simulated interferometric visibilities for low-redshift HI intensity mapping, beyond the flat-sky approximation used in the Generalised Visibility Internal Linear Combination analysis.

Background

The visibility simulations neglect the w-term, which describes the deviation of the interferometer from a coplanar array and becomes more important for off-zenith observations such as the DEEP2 field. This simplification ensures that the simulated visibilities exactly satisfy the flat-sky visibility equation, but it is not fully realistic.

A treatment incorporating the w-term is therefore left unresolved as a methodological extension needed for more realistic simulations and foreground-cleaning studies.

References

Although this assumption is not fully realistic, it ensures that the simulated visibilities exactly satisfy the flat-sky visibility equation. A proper treatment of the $w$-term is left for future work.

— Generalised Visibility ILC: a new foreground mitigation strategy for interferometric HI intensity mapping in the low-redshift Universe  (2609.19276 - Ruiz-Granda et al., 16 Sep 2026) in Section 2.4, subsection “Instrument”