Improved background subtraction for the Sloan Digital Sky Survey images

TL;DR

This paper introduces an improved background subtraction method for SDSS images, enhancing the detection and photometry of large galaxies by reducing size-dependent biases present in previous catalogs.

Contribution

The authors develop a new background subtraction technique that significantly improves photometric accuracy for large galaxies in SDSS data, addressing biases in standard methods.

Findings

No size-dependent bias in galaxy fluxes up to 100 arcsec radii

Standard SDSS catalog underestimates fluxes by about 1.5 mag for large galaxies

Method applied to all SDSS-III DR8 images and publicly available

Abstract

We describe a procedure for background subtracting Sloan Digital Sky Survey (SDSS) imaging that improves the resulting detection and photometry of large galaxies on the sky. Within each SDSS drift scan run, we mask out detected sources and then fit a smooth function to the variation of the sky background. This procedure has been applied to all SDSS-III Data Release 8 images, and the results are available as part of that data set. We have tested the effect of our background subtraction on the photometry of large galaxies by inserting fake galaxies into the raw pixels, reanalyzing the data, and measuring them after background subtraction. Our technique results in no size-dependent bias in galaxy fluxes up to half-light radii of 100 arcsec; in contrast, for galaxies of that size the standard SDSS photometric catalog underestimates fluxes by about 1.5 mag. Our results represent a substantial improvement over the standard SDSS catalog results and should form the basis of any analysis of nearby galaxies using the SDSS imaging data.