IMPROVED GALEX UV PHOTOMETRY FOR 700,000 SDSS GALAXIES

Osborne, Salim, Boquien, Dickinson, and Arnouts

Motivation

The first and so far the only wide-area UV sky survey was performed by the Galaxy Evolution Explorer (GALEX) satellite. GALEX obtained imaging data for almost the entire high-latitude sky in both far-UV (FUV) and near-UV (NUV) passbands. GALEX UV photometry is essential for constraining the dust content and star formation rate of galaxies, and complements the 5-band optical photometry of the Sloan Digital Sky Survey (SDSS). However, the relatively crude 5-arcsec resolution of GALEX leads to potential blending of sources and biased UV fluxes in the SourceExtractor pipeline photometry. The blending problem can be solved by performing forced photometry using source positions from SDSS and model profiles.

New photometry

In Osborne et al. 2023, we performed forced model photometry using SDSS priors on GALEX imaging to obtain improved UV fluxes of all (~700,000) galaxies included in the GALEX-SDSS-WISE Legacy Catalog (GSWLC; Salim et al. 2016). We performed forced photometry using modified EMphot v2.0 software (Conseil et al. 2011).

Catalog Description

We split our catalogs based on the depth of the UV imaging in the same way as GSWLC. All galaxies from GSWLC are included regardless of whether they have UV photometry, so the mapping between the EMphot and original GSWLC catalogs (of the same depth) is one to one and the galaxies are listed in the same order. Note that photometry files have a header line, whereas GSWLC files do not.

A description of the data columns (which are the same for each catalog) is provided here.

The combined photometry is the error-weighted average of all detections, and is preferable in general since it maximizes the signal-to-noise. The best-tile photometry may be preferred if one desires measurements with uniform depth.