SYNMAG Photometry: A Fast Tool for Catalog-Level Matched Colors of Extended Sources

TL;DR

SYNMAG photometry provides a fast, catalog-level method for obtaining matched aperture fluxes of extended sources across different surveys, improving efficiency without reprocessing imaging data.

Contribution

The paper introduces SYNMAG, a novel, computationally efficient technique for generating matched aperture photometry using galaxy profile fits, eliminating the need for reprocessing imaging data.

Findings

SYNMAG achieves comparable accuracy to traditional methods in color and redshift estimation.

The method significantly reduces computational time for large survey datasets.

Application to SDSS and UKIDSS data demonstrates its effectiveness.

Abstract

Obtaining reliable, matched photometry for galaxies imaged by different observatories represents a key challenge in the era of wide-field surveys spanning more than several hundred square degrees. Methods such as flux fitting, profile fitting, and PSF homogenization followed by matched-aperture photometry are all computationally expensive. We present an alternative solution called "synthetic aperture photometry" that exploits galaxy profile fits in one band to efficiently model the observed, PSF-convolved light profile in other bands and predict the flux in arbitrarily sized apertures. Because aperture magnitudes are the most widely tabulated flux measurements in survey catalogs, producing synthetic aperture magnitudes (SYNMAGs) enables very fast matched photometry at the catalog level, without reprocessing imaging data. We make our code public and apply it to obtain matched photometry between SDSS ugriz and UKIDSS YJHK imaging, recovering red-sequence colors and photometric redshifts with a scatter and accuracy as good as if not better than FWHM-homogenized photometry from the GAMA Survey. Finally, we list some specific measurements that upcoming surveys could make available to facilitate and ease the use of SYNMAGs.