Background Subtraction Uncertainty from Submillimetre to Millimetre Wavelengths

TL;DR

This paper quantifies the uncertainty in background subtraction for galaxy observations at submillimetre to millimetre wavelengths, providing formulas and code to improve error analysis in flux measurements.

Contribution

It introduces simple formulae for estimating background subtraction uncertainty and makes the calculation code publicly available.

Findings

Uncertainty depends on wavelength and aperture size.

Formulas help assess when background uncertainty is significant.

Code availability facilitates practical application.

Abstract

Photometric observations of galaxies at submillimetre to millimetre wavelengths (50 - 1000 GHz) are susceptible to spatial variations in both the background CMB temperature and CIB emission that can be comparable to the flux from the target galaxy. We quantify the residual uncertainty when background emission inside a circular aperture is estimated by the mean flux in a surrounding annular region, assumed to have no contribution from the source of interest. We present simple formulae to calculate this uncertainty as a function of wavelength and aperture size. Drawing on examples from the literature, we illustrate the use of our formalism in practice and highlight cases in which uncertainty in the background subtraction needs to be considered in the error analysis. We make the code used to calculate the uncertainties publicly available on the web.