AGN jets versus accretion as reionization sources

Abstract

Cosmic reionization put an end to the dark ages that came after the recombination era. Observations seem to favor the scenario where massive stars generating photons in low-mass galaxies were responsible for the bulk of reionization. Even though a possible contribution from accretion disks of active galactic nuclei (AGN) has been widely considered, they are currently thought to have had a minor role in reionization. Our aim is to study the possibility that AGN contributed to reionization not only through their accretion disks, but also through ionizing photons coming from the AGN jets interacting with the IGM. We adopt an empirically derived AGN luminosity function at $z\simeq 6$, use X-ray observations to correct it for the presence of obscured sources, and estimate the density of jetted AGN. We then use analytical calculations to derive the fraction of jet energy that goes into ionizing photons. Finally, we compute the contribution of AGN jets to the H II volume filling factor at redshifts $z\simeq 15-5$. We show that the contribution of the AGN jet lobes to the reionization of the Universe at $z\sim 6$ might have been as high as $\gtrsim 10$\% of that of star-forming galaxies, under the most favorable conditions of jetted and obscuration fraction. The contribution of AGN to the reionization, while most likely not dominant, could have been higher than previously assumed, thanks to the radiation originated in the jet lobes.

7 pages, 3 figures, accepted for publication in A&A

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Cited by in corpus (5)

• On the AGN nature of two UV bright sources at z_spec~5.5 in the CANDELS fields: an update of the AGN space density at M1450~-22.5
• The Lyman Continuum Escape Fraction of Galaxies and AGN in the GOODS Fields
• Direct observation of an extended X-ray jet at $z$=6.1
• Discovery and characterization of 25 new quasars at 4.6 < z < 6.9 from wide-field multi-band surveys
• Emission Line Galaxies in the SHARDS Hubble Frontier Fields II: Limits on Lyman-Continuum Escape Fractions of Lensed Emission Line Galaxies at Redshifts 2 < z < 3.5