The SDSS Coadd: 275 deg^2 of Deep SDSS Imaging on Stripe 82

TL;DR

This paper details the creation and characterization of a deep, wide-area coadded imaging dataset from SDSS Stripe 82, reaching 2 magnitudes deeper than single-pass data, enabling various astrophysical analyses.

Contribution

It introduces a comprehensive method for constructing, calibrating, and modeling the PSF of a deep coadded SDSS dataset covering 275 deg$^2$, with detailed validation and potential applications.

Findings

Median seeing of 1.1 arcsec in r-band

Calibration accuracy within 1%

Good PSF modeling suitable for precision photometry

Abstract

We present details of the construction and characterization of the coaddition of the Sloan Digital Sky Survey Stripe 82 \ugriz\ imaging data. This survey consists of 275 deg$^2$ of repeated scanning by the SDSS camera of $2.5\arcdeg$ of $\delta$ over $-50\arcdeg \le \alpha \le 60\arcdeg$ centered on the Celestial Equator. Each piece of sky has $\sim 20$ runs contributing and thus reaches $\sim2$ magnitudes fainter than the SDSS single pass data, i.e. to $r\sim 23.5$ for galaxies. We discuss the image processing of the coaddition, the modeling of the PSF, the calibration, and the production of standard SDSS catalogs. The data have $r$-band median seeing of 1.1\arcsec, and are calibrated to $\le 1%$. Star color-color, number counts, and psf size vs modelled size plots show the modelling of the PSF is good enough for precision 5-band photometry. Structure in the psf-model vs magnitude plot show minor psf mis-modelling that leads to a region where stars are being mis-classified as galaxies, and this is verified using VVDS spectroscopy. As this is a wide area deep survey there are a variety of uses for the data, including galactic structure, photometric redshift computation, cluster finding and cross wavelength measurements, weak lensing cluster mass calibrations, and cosmic shear measurements.