English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We use a wide-field (0.9 square degree) X-ray sample with optical and GALEXultraviolet observations to measure the contribution of Active Galactic Nuclei(AGNs) to the ionizing flux as a function of redshift. Our analysis shows thatthe AGN contribution to the metagalactic ionizing background peaks around z=2.The measured values of the ionizing background from the AGNs are lower thanprevious estimates and confirm that ionization from AGNs is insufficient tomaintain the observed ionization of the intergalactic medium (IGM) at z>3. Weshow that only sources with broad lines in their optical spectra havedetectable ionizing flux and that the ionizing flux seen in an AGN is notcorrelated with its X-ray color. We also use the GALEX observations of theGOODS-N region to place a 2-sigma upper limit of 0.008 on the averageionization fraction fnu(700 A)/fnu(1500 A) for 626 UV selected galaxies in theredshift range z=0.9-1.4. We then use this limit to estimate an upper bound tothe galaxy contribution in the redshift range z=0-5. If the z~1.15 ionizationfraction is appropriate for higher redshift galaxies, then contributions fromthe galaxy population are also too low to account for the IGM ionization at thehighest redshifts (z>4).

Measuring the Sources of the Intergalactic Ionizing Flux