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 Lyα emitters (LAEs) from z ∼ 2 to z ∼ 6 in 16 redshift slices (SC4K). We present new Lyα luminosity functions (LFs) covering a co-moving volume of ∼ 10 8 Mpc 3 . SC4K extensively complements ultradeep surveys, jointly covering over 4 dex in Lyα luminosity and revealing a global (2.5 < z < 6) synergy LF with α = −1.93 +0.12 −0.12 , log 10 Φ * Lyα = −3.45 +0.22 −0.29 Mpc −3 and log 10 L * Lyα = 42.93 +0.15 −0.11 erg s −1 . The Schechter component of the Lyα LF reveals a factor ∼ 5 rise in L * Lyα and a ∼ 7× decline in Φ * Lyα from z ∼ 2 to z ∼ 6. The data reveal an extra power-law (or Schechter) component above L Lyα ≈ 10 43.3 erg s −1 at z ∼ 2.2 − 3.5 and we show that it is partially driven by X-ray and radio AGN, as their Lyα LF resembles the excess. The power-law component vanishes and/or is below our detection limits above z > 3.5, likely linked with the evolution of the AGN population. The Lyα luminosity density rises by a factor ∼ 2 from z ∼ 2 to z ∼ 3 but is then found to be roughly constant (1.1 +0.2 −0.2 × 10 40 erg s −1 Mpc −3 ) to z ∼ 6, despite the ∼ 0.7 dex drop in UV luminosity density. The Lyα/UV luminosity density ratio rises from 4±1% to 30 ± 6% from z ∼ 2.2 to z ∼ 6. Our results imply a rise of a factor of ≈ 2 in the global ionisation efficiency (ξ ion ) and a factor ≈ 4 ± 1 in the Lyα 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 Lyα photons to escape.

We present results from the largest contiguous narrow-band survey in the near-infrared. We have used WIRCam/CFHT and the lowOH2 filter (1.187 ± 0.005 µm) to survey ≈10 deg 2 of contiguous extragalactic sky in the SA22 field. A total of ∼ 6000 candidate emission-line galaxies are found. We use deep ugrizJK data to obtain robust photometric redshifts. We combine our data with the High-redshift Emission Line Survey (HiZELS), explore spectroscopic surveys (VVDS, VIPERS) and obtain our own spectroscopic follow-up with KMOS, FMOS and MOSFIRE to derive large samples of high-redshift emission-line selected galaxies: 3471 Hα emitters at z = 0.8, 1343 [OIII]+Hβ emitters at z = 1.4 and 572 [OII] emitters at z = 2.2. We probe co-moving volumes of > 10 6 Mpc 3 and find significant over-densities, including an 8.5 σ (spectroscopically confirmed) over-density of Hα emitters at z = 0.81. We derive Hα, [OIII]+Hβ and [OII] luminosity functions at z = 0.8, 1.4, 2.2, respectively, and present implications for future surveys such as Euclid. Our uniquely large volumes/areas allow us to sub-divide the samples in thousands of randomised combinations of areas and provide a robust empirical measurement of sample/cosmic variance. We show that surveys for star-forming/emission-line galaxies at a depth similar to ours can only overcome cosmicvariance (errors < 10%) if they are based on volumes > 5 × 10 5 Mpc 3 ; errors on L * and φ * due to sample (cosmic) variance on surveys probing ∼ 10 4 Mpc 3 and ∼ 10 5 Mpc 3 are typically very high: ∼ 300% and ∼ 40 − 60%, respectively.

We present the second data release of the Large Early Galaxy Astrophysics Census (LEGA-C), an ESO 130−night public spectroscopic survey conducted with VIMOS on the Very Large Telescope. We release 1988 spectra with typical continuum S/N 20Å −1 of galaxies at 0.6 z 1.0, each observed for ∼ 20 hours and fully reduced with a custom-built pipeline. We also release a catalog with spectroscopic redshifts, emission line fluxes, Lick/IDS indices, and observed stellar and gas velocity dispersions that are spatially integrated quantities including both rotational motions and genuine dispersion. To illustrate the new parameter space in the intermediate redshift regime probed by LEGA-C we explore relationships between dynamical and stellar population properties. The star-forming galaxies typically have observed stellar velocity dispersions of ∼ 150 km s −1 and strong Hδ absorption (Hδ A ∼ 5Å), while passive galaxies have higher observed stellar velocity dispersions (∼ 200 km s −1 ) and weak Hδ absortion (Hδ A ∼ 0Å). Strong [OIII]5007/Hβ ratios tend to occur mostly for galaxies with weak Hδ A or galaxies with higher observed velocity dispersion. Beyond these broad trends, we find a large diversity of possible combinations of rest-frame colors, absorption line strengths and emission line detections, illustrating the utility of spectroscopic measurements to more accurately understand galaxy evolution. By making the spectra and value-added catalogs publicly available we encourage the community to take advantage of this very substantial investment in telescope time provided by ESO.

We explore deep rest-frame UV to FIR data in the COSMOS field to measure the individual spectral energy distributions (SED) of the ∼ 4000 SC4K (Sobral et al. 2018a) Lyman-α (Lyα) emitters (LAEs) at z ∼ 2 − 6. We find typical stellar masses of 10 9.3±0.6 M and star formation rates (SFR) of SFR SED = 4.5 +8.8 −2.5 M yr −1 and SFR Lyα = 5.9 +6.3 −2.6 M yr −1 , combined with very blue UV slopes of β = −2.0 +0.3 −0.5 , but with significant variations within the population. M UV and β are correlated in a similar way to UV-selected sources, but LAEs are consistently bluer. This suggests that LAEs are the youngest and/or most dust-poor subset of the UV-selected population. We also study the Lyα rest-frame equivalent width (EW 0 ) and find 45 "extreme" LAEs with EW 0 > 240Å (3 σ), implying a low number density of (7±1)×10 −7 Mpc −3 . Overall, we measure little to no evolution of the Lyα EW 0 and scale length parameter (w 0 ) which are consistently high (EW 0 = 140 +280 −70Å , w 0 = 129 +11 −11Å ) from z ∼ 6 to z ∼ 2 and below. However, w 0 is anti-correlated with M UV and stellar mass. Our results imply that sources selected as LAEs have a high Lyα escape fraction (f esc,Lyα ) irrespective of cosmic time, but f esc,Lyα is still higher for UV-fainter and lower mass LAEs. The least massive LAEs (< 10 9.5 M ) are typically located above the star formation "Main Sequence" (MS), but the offset from the MS decreases towards z ∼ 6 and towards 10 10 M . Our results imply a lack of evolution in the properties of LAEs across time and reveals the increasing overlap in properties of LAEs and UV-continuum selected galaxies as typical star-forming galaxies at high redshift effectively become LAEs.