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The CALYMHA survey: Lyα luminosity function and global escape fraction of Lyα photons at z = 2.23

D. Sobral, J. Matthee, P. Best, A. Stroe, H. J. A. R÷ttgering, I. Oteo, I. Smail, L. Morabito, A. Paulino-Afonso

Abstract
We present the CAlibrating LYMan-α with Hα (CALYMHA) pilot survey and new results on Lyman α (Lyα) selected galaxies at z∼2. We use a custom-built Lyα narrow-band filter at the Isaac Newton Telescope, designed to provide a matched volume coverage to the z=2.23 Hα HiZELS survey. Here, we present the first results for the COSMOS and UDS fields. Our survey currently reaches a 3σ line flux limit of ∼4 × 10−17 erg s−1 cm−2, and a Lyα luminosity limit of ∼1042.3 erg s−1. We find 188 Lyα emitters over 7.3 × 105 Mpc3, but also find significant numbers of other line-emitting sources corresponding to He II,; C III] and C IV emission lines. These sources are important contaminants, and we carefully remove them, unlike most previous studies. We find that the Lyα luminosity function at z=2.23 is very well described by a Schechter function up to LLy α ≈ 1043 erg s−1 with L=1042.59−0.08+0.16 erg s−1, ϕ=10−3.09−0.34+0.14 Mpc−3 and α=−1.75; ± 0.25. Above LLy α ≈ 1043 erg s−1, the Lyα luminosity function becomes power-law like, driven by X-ray AGN. We find that Lyα-selected emitters have a high escape fraction of 37±7 per cent, anticorrelated with Lyα luminosity and correlated with Lyα equivalent width. Lyα emitters have ubiquitous large (≈40 kpc) Lyα haloes, ∼2 times larger than their Hα extents. By directly comparing our Lyα and Hα luminosity functions, we find that the global/overall escape fraction of Lyα photons (within a 13 kpc radius) from the full population of star-forming galaxies is 5.1±0.2 per cent at the peak of the star formation history. An extra 3.3±0.3 per cent of Lyα photons likely still escape, but at larger radii.

Keywords
galaxies: evolution, galaxies: haloes, galaxies: high-redshift, galaxies: luminosity function, mass function, galaxies: statistics, cosmology: observations

Monthly Notices of the Royal Astronomical Society
Volume 466, Issue 1, Page 17
2017 April

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Instituto de Astrof├şsica e Ci├¬ncias do Espa├žo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Funda├ž├úo para a Ci├¬ncia e a Tecnologia
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