Active Galactic Nuclei Selected from GALEX Spectroscopy: The Ionizing Source Spectrum at z~1

Abstract

We use a complete sample of Lya emission-line selected AGNs obtained from nine deep blank fields observed with the grism spectrographs on the Galaxy Evolution Explorer (GALEX) satellite to measure the normalization and spectral shape of the AGN contribution to the ionizing background (rest-frame wavelengths 700-900 A) at z~1. Our sample consists of 139 sources selected in the redshift range z=0.65-1.25 in the near-ultraviolet (NUV; 2371 A central wavelength) channel. The area covered is 8.2 square degrees to a NUV magnitude of 20.5 (AB) and 0.92 square degrees at the faintest magnitude limit of 21.8. The GALEX AGN luminosity function agrees well with those obtained using optical and X-ray AGN samples, and the measured redshift evolution of the ionizing volume emissivity is similar to that previously obtained by measuring the GALEX far-ultraviolet (FUV; 1528 A central wavelength) magnitudes of an X-ray selected sample. For the first time we are able to construct the shape of the ionizing background at z~1 in a fully self-consistent way.