GALEX-SDSS Catalogs for Statistical Studies

TL;DR

This paper analyzes GALEX and SDSS catalogs, focusing on their statistical properties, source matching, and selection functions to facilitate large-scale astrophysical studies.

Contribution

It introduces a geometric approach to define clean catalogs, revises the UV source merging strategy, and provides publicly available crossmatch catalogs for statistical research.

Findings

Defined well-understood selection functions for GALEX catalogs

Revised the band merging strategy for UV sources

Provided public crossmatch catalogs for statistical analyses

Abstract

We present a detailed study of the Galaxy Evolution Explorer's photometric catalogs with special focus on the statistical properties of the All-sky and Medium Imaging Surveys. We introduce the concept of primaries to resolve the issue of multiple detections and follow a geometric approach to define clean catalogs with well-understood selection functions. We cross-identify the GALEX sources (GR2+3) with Sloan Digital Sky Survey (DR6) observations, which indirectly provides an invaluable insight about the astrometric model of the UV sources and allows us to revise the band merging strategy. We derive the formal description of the GALEX footprints as well as their intersections with the SDSS coverage along with analytic calculations of their areal coverage. The crossmatch catalogs are made available for the public. We conclude by illustrating the implementation of typical selection criteria in SQL for catalog subsets geared toward statistical analyses, e.g., correlation and luminosity function studies.