Variable AGN in the GALEX Time Domain Survey

TL;DR

This study identifies and characterizes variable active galactic nuclei (AGNs) in the GALEX Time-Domain Survey using UV variability, optical, IR, and SED methods, revealing diverse AGN populations including low-mass candidates.

Contribution

It introduces a UV variability-based method for AGN detection and compares it with traditional optical and IR selection techniques, uncovering AGNs missed by other methods.

Findings

48 high-probability AGN candidates identified

Multiple selection methods reveal different AGN subsets

Low-mass AGN candidates discovered via UV variability

Abstract

We searched the Northern Hemisphere Fields of the GALEX Time-Domain Survey (TDS) for galaxies with UV variability indicative of active galactic nuclei (AGNs). We identified 48 high-probability candidate AGNs from a parent sample of 1819 galaxies in the NASA Sloan Atlas (NSA) catalog. We further characterized these systems using optical spectroscopic diagnostics, WISE IR color selection criteria, and spectral energy distribution (SED) modeling. Of the 48 candidates, eight were identified as AGNs from optical emission lines, two were identified by their IR colors, and 28 were identified through spectral energy decomposition. Observational biases of each selection method are discussed in connecting these AGNs subsamples to another. By selecting AGNs based on UV variability, we also identified six low-mass AGNs candidates, all of which would have been missed by spectroscopic selection.