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

TL;DR

This study uses GALEX spectroscopy to measure the ionizing background at z~1, providing a self-consistent shape of the ionizing spectrum and confirming the consistency of AGN luminosity functions across different wavelengths.

Contribution

First to construct the ionizing background shape at z~1 using a spectroscopic AGN sample from GALEX, confirming the luminosity function's consistency across wavelengths.

Findings

AGN luminosity function agrees with optical and X-ray samples

Redshift evolution of ionizing emissivity matches previous FUV measurements

Constructed the ionizing background shape at z~1 in a self-consistent manner

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.