The most luminous H α emitters atz∼ 0.8–2.23 from HiZELS: evolution of AGN and star-forming galaxies

• DOI: 10.1093/mnras/stw022
• Publication Date: 2016-02-05T01:43:24Z
• Authors: David Sobral; Saul A. Kohn; Philip N. Best; Ian Smail; Chris M. Harrison; John Stott; João Calhau; Jorryt Matthee
• Keywords: observations. [Cosmology]; Cosmology and Nongalactic Astrophysics (astro-ph.CO); Cosmology: observations; Galaxies: high-redshift; Galaxies: evolution; FOS: Physical sciences; evolution [Galaxies]; 530; Astrophysics - Astrophysics of Galaxies; 01 natural sciences; 520; high-redshift [Galaxies]; Astrophysics of Galaxies (astro-ph.GA); 0103 physical sciences; Astrophysics - Cosmology and Nongalactic Astrophysics

16 pages, 10 figures. Accepted for publication in MNRAS<br/>We use new near-infrared spectroscopic observations to investigate the nature and evolution of the most luminous H��(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 $L_{H��}>L_{H��}^*$, 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 $L_{H��}/L_{H��}^*(z)$. While $L_{H��}80%), the most luminous Ha emitters ($L_{H��}>10L_{H��}^*(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��}>L^*_{H��}(z)$) contribute the same fractional amount of ~15% to the total star-formation rate density, at least up to z=2.23.<br/>