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Lookup NU author(s): Dr Christopher HarrisonORCiD
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© 2016 The Authors. We use new near-infrared spectroscopic observations to investigate the nature and evolution of the most luminous Hα emitters at z ~ 0.8-2.23, which evolve strongly in number density over this period, and compare them to more typical Hα emitters. We study 59 luminous Hα emitters with LHα > L Hα*, 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 ± 8 per cent are active galactic nuclei [AGNs; 80 ± 30 per cent of these AGNs are broad-line AGNs, BL-AGNs], and we find little to no evolution in the AGN fraction with redshift, within the errors. However, the AGN fraction increases strongly with Hα luminosity and correlates best with LHα/LHα* (z). While LHα ≤ LHα* (z) Hα emitters are largely dominated by star-forming galaxies (> 80 per cent), the most luminous Hα emitters (LHα > 10LHα*(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 Hα luminosity, we find a factor of ~1300 evolution in the star formation rate density from z = 0 to 2.23. This is much stronger than the evolution from typical Hα star-forming galaxies and in line with the evolution seen for constant luminosity cuts used to select 'ultraluminous' infrared galaxies and/or sub-millimetre galaxies. By taking into account the evolution in the typical Hα luminosity, we show that the most strongly starforming Hα-selected galaxies at any epoch (LHα > LHα* (z)) contribute the same fractional amount of ≈ 15 per cent to the total star formation rate density, at least up to z = 2.23.
Author(s): Sobral D, Kohn SA, Best PN, Smail I, Harrison CM, Stott J, Calhau J, Matthee J
Publication type: Article
Publication status: Published
Journal: Monthly Notices of the Royal Astronomical Society
Print publication date: 01/04/2016
Online publication date: 04/02/2016
Acceptance date: 04/01/2016
ISSN (print): 0035-8711
ISSN (electronic): 1365-2966
Publisher: Oxford University Press
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