Assessing Galaxy Limiting Magnitudes in Large Optical Surveys

TL;DR

This paper introduces an empirical method to accurately estimate galaxy limiting magnitudes across large sky surveys, improving the understanding of survey depth and galaxy detection completeness for cosmological analyses.

Contribution

It presents a new empirical approach for estimating galaxy limiting magnitudes directly from survey data, enabling more accurate depth maps for large photometric surveys.

Findings

Depth maps enable unbiased galaxy correlation function estimation.

Method applied to SDSS DR8 and combined with deeper imaging.

Provides HEALPix format limiting magnitude maps for SDSS DR8.

Abstract

Large scale structure measurements require accurate and precise knowledge of the survey depth --- typically expressed in the form of a limiting magnitude --- as a function of position on the sky. To date, most surveys only compute the point-source limiting magnitude measured within a fixed metric aperture. However, this quantity is ill suited to describe the limiting depth of galaxies, which depends on the detailed interplay of survey systematics with galaxy shapes and sizes. We describe an empirical method for directly estimating the limiting magnitude for large photometric surveys, and apply it to $\sim10,000\,\mathrm{deg}^{2}$ of SDSS DR8 data. Combined with deeper imaging from SDSS Stripe 82 and CFHTLens, we are able to use these depth maps to estimate the location-dependent galaxy detection completeness at any point within the full BOSS DR8 survey region. We show that these maps can be used to construct random points suitable for unbiased estimation of correlation functions for galaxies near the survey limiting magnitude. Finally, we provide limiting magnitude maps for galaxies in SDSS DR8 in HEALPix format with NSIDE=2048.