An On-Sky Atmospheric Calibration of SPT-SLIM

Abstract

We present the methodology and results of the on-sky responsivity calibration of the south pole telescope shirokoff line intensity mapper (SPT-SLIM). SPT-SLIM is a pathfinder line intensity mapping experiment utilizing the on-chip spectrometer technology, and was first deployed during the 2024–2025 Austral Summer season on the south pole telescope. During the two-week on-sky operation of SPT-SLIM, we performed periodic measurements of the detector response as a function of the telescope elevation angle. Combining these data with atmospheric opacity measurements from an on-site atmospheric tipping radiometer, simulated South Pole atmospheric spectra, and measured detector spectral responses, we construct estimates for the responsivity of SPT-SLIM detectors to sky loading. We then use this model to calibrate observations of the Moon taken by SPT-SLIM, cross-checking the result against the known brightness temperature of the Moon as a function of its phase.