Sky Subtraction in an Era of Low Surface Brightness Astronomy

TL;DR

This paper evaluates and improves sky subtraction techniques for low surface brightness astronomy, demonstrating that combining Source Extractor with novel masking yields more accurate sky estimates and better faint object detection.

Contribution

It introduces a new approach combining Source Extractor with source model masking to enhance sky estimation accuracy in low surface brightness surveys.

Findings

Source Extractor with masking improves sky estimates by up to tenfold.

The method enhances detection of faint objects in simulated crowded fields.

Performance varies with field density and object brightness, but overall shows significant improvement.

Abstract

The Vera C. Rubin Observatory Wide-Fast Deep (WFD) sky survey will reach unprecedented surface brightness depths over tens of thousands of square degrees. Surface brightness photometry has traditionally been a challenge. Current algorithms which combine object detection with sky estimation systematically over-subtract the sky, biasing surface brightness measurements at the faint end and destroying or severely compromising low surface brightness light. While it has recently been shown that properly accounting for undetected faint galaxies and the wings of brighter objects can in principle recover a more accurate sky estimate, this has not yet been demonstrated in practice. Obtaining a consistent spatially smooth underlying sky estimate is particularly challenging in the presence of representative distributions of bright and faint objects. In this paper we use simulations of crowded and uncrowded fields designed to mimic Hyper Suprime-Cam data to perform a series of tests on the accuracy of the recovered sky. Dependence on field density, galaxy type and limiting flux for detection are all considered. Several photometry packages are utilised: Source Extractor, Gnuastro, and the LSST Science Pipelines. Each is configured in various modes, and their performance at extreme low surface brightness analysed. We find that the combination of the Source Extractor software package with novel source model masking techniques consistently produce extremely faint output sky estimates, by up to an order of magnitude, as well as returning high fidelity output science catalogues.