The most luminous H$α$ emitters at z~0.8-2.23 from HiZELS:evolution of AGN and star-forming galaxies

Sobral, David and Kohn, Saul A. and Best, Philip N. and Smail, Ian and Harrison, Chris M. and Stott, John and Calhau, João and Matthee, Jorryt (2016) The most luminous H$α$ emitters at z~0.8-2.23 from HiZELS:evolution of AGN and star-forming galaxies. Monthly Notices of the Royal Astronomical Society, 457 (2). pp. 1739-1752. ISSN 0035-8711

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We use new near-infrared spectroscopic observations to investigate the nature and evolution of the most luminous H\alpha (Ha) emitters at z~0.8-2.23, which evolve strongly in number density over this period, and compare them to more typical Ha emitters. We study 59 luminous Ha emitters with $L_{H\alpha}>L_{H\alpha}^*$, roughly equally split per redshift slice at z~0.8, 1.47 and 2.23 from the HiZELS and CF-HiZELS surveys. We find that, overall, 30$\pm$8% are AGN (80$\pm$30% of these AGN are broad-line AGN, BL-AGN), and we find little to no evolution in the AGN fraction with redshift, within the errors. However, the AGN fraction increases strongly with Ha luminosity and correlates best with $L_{H\alpha}/L_{H\alpha}^*(z)$. While $L_{H\alpha} 80%), the most luminous Ha emitters ($L_{H\alpha}>10L_{H\alpha}^*(z)$) at any cosmic time are essentially all BL-AGN. Using our AGN-decontaminated sample of luminous star-forming galaxies, and integrating down to a fixed Ha luminosity, we find a factor of ~1300x evolution in the star formation rate density from z=0 to z=2.23. This is much stronger than the evolution from typical Ha star-forming galaxies and in line with the evolution seen for constant luminosity cuts used to select "Ultra-Luminous" Infrared Galaxies and/or sub-millimetre galaxies. By taking into account the evolution in the typical Ha luminosity, we show that the most strongly star-forming Ha-selected galaxies at any epoch ($L_{H\alpha}>L^*_{H\alpha}(z)$) contribute the same fractional amount of ~15% to the total star-formation rate density, at least up to z=2.23.

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Journal Article
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Monthly Notices of the Royal Astronomical Society
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This is a pre-copy-editing, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The definitive publisher-authenticated version David Sobral, Saul A. Kohn, Philip N. Best, Ian Smail, Chris M. Harrison, John Stott, João Calhau, and Jorryt Matthee The most luminous H α emitters at z ∼ 0.8–2.23 from HiZELS: evolution of AGN and star-forming galaxies MNRAS (April 01, 2016) Vol. 457 1739-1752 is available online at:
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18 Jan 2016 10:02
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22 Jan 2021 05:55