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Rights statement: 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, Sérgio Santos, Jorryt Matthee, Ana Paulino-Afonso, Bruno Ribeiro, João Calhau, Ali A Khostovan; Slicing COSMOS with SC4K: the evolution of typical Ly α emitters and the Ly α escape fraction from z ∼ 2 to 6, Monthly Notices of the Royal Astronomical Society, Volume 476, Issue 4, 1 June 2018, Pages 4725–4752, is available online at: https://doi.org/10.1093/mnras/sty378 MNRAS in press. 23 pages + Appendices with SC4K catalogue and LFs. SC4K catalogue of LAEs, SC4K LFs and the S-SC4K compilation are available (https://goo.gl/q9yfKo) prior to publication

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## Slicing COSMOS with SC4K: the evolution of typical Lya emitters and the Lya escape fraction from z~2 to z~6

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Journal publication date 1/06/2018 Monthly Notices of the Royal Astronomical Society 4 476 28 4725-4752 Published 14/02/18 English

### Abstract

We present and explore deep narrow- and medium-band data obtained with the Subaru and the Isaac Newton telescopes in the ~2 deg$^2$ COSMOS field. We use these data as an extremely wide, low-resolution (R~20-80) IFU survey to slice through the COSMOS field and obtain a large sample of ~4000 Lyman-$\alpha$ (Lya) emitters from z~2 to z~6 in 16 redshift slices (SC4K). We present new Lya luminosity functions (LFs) covering a co-moving volume of ~10$^8$Mpc$^3$. SC4K extensively complements ultra-deep surveys, jointly covering over 4 dex in Lya luminosity and revealing a global (2.5z 3.5, likely linked with the evolution of the AGN population. The Lya luminosity density rises by a factor ~2 from z~2 to z~3 but is then found to be roughly constant (~$1.1\times10^{40}$ erg s$^{-1}$ Mpc$^{-3}$) to z~6, despite the ~0.7 dex drop in UV luminosity density. The Lya/UV luminosity density ratio rises from $4\pm1$% to $30\pm6$% from z~2.2 to z~6. Our results imply a rise of a factor of ~2 in the global ionisation efficiency ($\xi_{\rm ion}$) and a factor ~$4\pm1$ in the Lya escape fraction from z~2 to z~6, hinting for evolution in both the typical burstiness/stellar populations and even more so in the typical ISM conditions allowing Ly$\alpha$ photons to escape.

### Bibliographic note

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, Sérgio Santos, Jorryt Matthee, Ana Paulino-Afonso, Bruno Ribeiro, João Calhau, Ali A Khostovan; Slicing COSMOS with SC4K: the evolution of typical Ly α emitters and the Ly α escape fraction from z ∼ 2 to 6, Monthly Notices of the Royal Astronomical Society, Volume 476, Issue 4, 1 June 2018, Pages 4725–4752, is available online at: https://doi.org/10.1093/mnras/sty378 In press. 23 pages + Appendices with SC4K catalogue and LFs. SC4K catalogue of LAEs, SC4K LFs and the S-SC4K compilation are available (https://goo.gl/q9yfKo) prior to publication