Origin of residual baseline artifacts in Setup 2 molecular-line maps

Identify the instrumental or observational origin of the residual stripe-like baseline distortions affecting the SO, HCN, and HCO+ molecular-line maps obtained with Galactic-longitude-only scans.

Background

The SO, HCN, and HCO+ observations used only scans in the Galactic-longitude direction, unlike the Setup 1 observations, which used both longitude and latitude scans. Irregular residual baseline distortions produce stripe-like artifacts in parts of the resulting maps, particularly in the SO map. Although the affected regions are described, the source of these distortions has not been established.

References

Because the Setup~2 lines (SO, HCN, and HCO$+$) were observed only in the x-scan direction, residual baseline distortions that could not be fully removed produce stripe-like features in the maps. These distortions appeared irregularly in some specific spectrometer bands and their origin remains unclear.

— The Nobeyama 45 m Survey of Shocked Molecular Gas in the Central Molecular Zone. I. Survey Data, Cloud Catalog, and SiO Line-Ratio Trends  (2608.25611 - Takekawa et al., 26 Aug 2026) in Section 2.3, Data Reduction and Data Products