Large Scale Spectrophotometric Relative Flux Calibration for the Roman High Latitude Wide Area Survey

TL;DR

This paper develops a simplified, high-precision relative flux calibration method for the Roman HLWAS spectroscopic data, achieving residuals below 1.5 mmag and adaptable to imaging surveys.

Contribution

It introduces a new calibration model with independent flat fields and wavelength-dependent throughput components, enhancing calibration accuracy and flexibility.

Findings

Residual calibration errors less than 1.5 mmag

Optimal dither range identified as 50-240"

Methodology adaptable to imaging surveys

Abstract

We consider the application of a ubercalibration-like relative flux calibration to the grism observations of the Roman High Latitude Wide Area Survey (HLWAS). We propose a simplified model of the calibration with an independent flat field for each detector in each exposure of the focal plane. In addition, we include two wavelength dependent components: a single wavelength throughput curve, modulated by a simple parabolic model for the throughput as a function of a source's focal plane position. We consider the impact of the dither scale, as well as the calibrator magnitude cuts. We show that the width of the calibration residuals can be reduced to less than 1.5 mmag, or 0.15% in flux, within the optimal dither range 50-240". This wide range allows for significant flexibility in optimising other parts of the observing program without diminishing the effectiveness of the relative flux calibration. We also discuss some improvements to the methodology that must be strongly considered before the calibration can be applied to real data. Finally, although we focused on spectroscopic component of the HLWAS here, our formalism and results should carry over to the imaging surveys as well.