📝 SummarXiv

Abstract

Line intensity maps have high dynamic range, and demand careful spectral and spatial calibration. We present a Bayesian framework for joint calibration and map-making using Gibbs sampling, which provides access to the full joint posterior of calibration and sky map parameters. Our data model incorporates instrumental noise based on the radiometer equation, capturing the coupling between noise level and system temperature without assuming a fixed noise amplitude. To enable unbiased and fast estimation of gain and system temperature, we develop an iterative generalised least squares (GLS) sampling method. Absolute flux calibration can be achieved either with external sources or internally using known signal injections, such as noise diodes. To handle stochastic gain variations, we introduce a $1/f$ noise model that avoids spurious periodic correlations in the time domain caused by the conventional assumption of diagonal DFT noise covariance. Furthermore, we implement this workflow in an efficient software package, using the Levinson algorithm and a polynomial emulator to reduce the computational complexity of noise parameter sampling, ensuring good scalability. Although demonstrated for auto-correlation measurements, the framework and techniques generalise to cross-correlation and interferometric data.