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Context. The escape of Lyman-α photons at redshifts greater than two is an ongoing subject of study and an important quantity to further understanding of Lyman-α emitters (LAEs), the transmission of Lyman-α photons through the interstellar medium and intergalactic medium, and the impact these LAEs have on cosmic reionisation. Aims. This study aims to assess the Lyman-α escape fraction, fesc, Lyα, over the redshift range 2.9 < z < 6.7, focusing on Very Large Telescope/Multi Unit Spectroscopic Explorer (VLT/MUSE) selected, gravitationally lensed, intrinsically faint LAEs. These galaxies are of particular interest as the potential drivers of cosmic reionisation. Methods. We assessed fesc, Lyα in two ways: through an individual study of 96 LAEs behind the A2744 lensing cluster, with James Webb Space Telescope/Near-Infrared Camera (JWST/NIRCam) and HST data, and through a study of the global evolution of fesc, Lyα using the state-of-the-art luminosity functions for LAEs and the UV-selected 'parent' population (dust-corrected). We compared these studies to those in the literature based on brighter samples. Results. We find a negligible redshift evolution of fesc, Lyα for our individual galaxies; it is likely that it was washed out by significant intrinsic scatter. We observed a more significant evolution towards higher escape fractions with decreasing UV magnitude and fit this relation. When comparing the two luminosity functions to derive fesc, Lyα in a global sense, we saw agreement with previous literature when integrating the luminosity functions to a bright limit. However, when integrating using a faint limit equivalent to the observational limits of our samples, we observed enhanced values of fesc, Lyα, particularly around z ∼ 6, where fesc, Lyα becomes consistent with 100% escape. This indicates for the faint regimes we sampled that galaxies towards reionisation tend to allow very large fractions of Lyman-α photons to escape. We interpret this as evidence of a lack of any significant dust in these populations; our sample is likely dominated by young, highly star-forming chemically unevolved galaxies. Finally, we assessed the contribution of the LAE population to reionisation using our latest values for fesc, Lyα and the LAE luminosity density. The dependence on the escape fraction of Lyman continuum photons is strong, but for values similar to those observed recently in z ∼ 3 LAEs and high-redshift analogues, LAEs could provide all the ionising emissivity necessary for reionisation. [ABSTRACT FROM AUTHOR]

Recent detections of extended Lyman-α halos around Lyα emitters (LAEs) have been reported on a regular basis, but their origin is still under investigation. Simulation studies predict that the outer regions of the extended halos contain a major contribution from the Lyα emission of faint, individually undetected LAEs. To address this matter from an observational angle, we used halo occupation distribution (HOD) modeling to reproduce the clustering of a spectroscopic sample of 1265 LAEs at 3 < z < 5 from the MUSE-Wide survey. We integrated the Lyα luminosity function to estimate the background surface brightness due to discrete faint LAEs. We then extended the HOD statistics inwards towards small separations and computed the factor by which the measured Lyα surface brightness is enhanced by undetected close physical neighbors. We considered various clustering scenarios for the undetected sources and compared the corresponding radial profiles. This enhancement factor from LAE clustering depends strongly on the spectral bandwidth Δv over which the Lyα emission is integrated and this value can amount to ≈20 − 40 for small values of Δv (around 200 − 400 km s−1) as achieved by recent studies utilizing integral-field spectrographic data. The resulting inferred Lyα surface brightness of faint LAEs ranges between (0.4 − 2)×1020 erg s−1 cm−2 arcsec−2, with a very slow radial decline outwards. Our results suggest that the outer regions of observed Lyα halos (R ≳ 50 pkpc) could indeed contain a strong component from external (but physically associated) LAEs, and may even be dominated by them. It is only for a relatively shallow faint-end slope of the Lyα luminosity function that this contribution from clustered LAEs would be rendered insignificant. We also confirm that the observed emission from the inner regions (R ≤ 20 − 30 pkpc) is too bright to be substantially affected by clustering. We compare our findings with predicted profiles from simulations and find good overall agreement. We outline possible future measurements to further constrain the impact of discrete undetected LAEs on observed extended Lyα halos. [ABSTRACT FROM AUTHOR]

The H α equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H α EW strongly anticorrelates with stellar mass as M −0.25 similar to the sSFR – stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H α EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H α emitters from the Ly α Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg2 area of COSMOS with a survey comoving volume of 1.1 × 105 Mpc3. We assume an intrinsic EW distribution to form mock samples of H α emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find that H α EW intrinsically correlates with stellar mass as W 0∝ M −0.16 ± 0.03 and decreases by a factor of ∼3 from 107 M⊙ to 1010 M⊙, while not correcting for selection effects steepens the correlation as M −0.25 ± 0.04. We find low-mass H α emitters to be ∼320 times more likely to have rest-frame EW>200 Å compared to high-mass H α emitters. Combining the intrinsic W 0–stellar mass correlation with an observed stellar mass function correctly reproduces the observed H α luminosity function, while not correcting for selection effects underestimates the number of bright emitters. This suggests that the W 0–stellar mass correlation when corrected for selection effects is physically significant and reproduces three statistical distributions of galaxy populations (line luminosity function, stellar mass function, EW distribution). At lower stellar masses, we find there are more high-EW outliers compared to high stellar masses, even after we take into account selection effects. Our results suggest that high sSFR outliers indicative of bursty star formation activity are intrinsically more prevalent in low-mass H α emitters and not a byproduct of selection effects. [ABSTRACT FROM AUTHOR]

We present our measurements of the H α, [O  iii ], and [O  ii ] luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 z  = 0.47 H α-, 3933 z  = 0.93 [O  iii ]-, and 5367 z  = 1.59 [O  ii ]-selected emission line galaxies in a 3 deg2 single, CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5σ depths of 8.2 × 10−18 erg s−1 cm−2 and comoving volumes of (1−7) × 105 Mpc3 making our survey one of the deepest narrow-band surveys. We select our emission line galaxies via spectroscopic confirmation, photometric redshifts, and colour–colour selections. We measure the observed luminosity functions for each sample and find best fits of |$\phi ^\star = 10^{-3.16^{+0.09}_{-0.09}}$| Mpc−3 and |$L^\star = 10^{41.72^{+0.09}_{-0.09}}$| erg s−1 for H α, |$\phi ^\star = 10^{-2.16^{+0.10}_{-0.12}}$| Mpc−3 and |$L^\star = 10^{41.38^{+0.07}_{-0.06}}$| erg s−1 for [O  iii ], and |$\phi ^\star = 10^{-1.97^{+0.07}_{-0.07}}$| Mpc−3 and |$L^\star = 10^{41.66^{+0.03}_{-0.03}}$| erg s−1 for [O  ii ], with α fixed to −1.75, −1.6, and −1.3, respectively. An excess of bright >1042 erg s−1 [O  iii ] emitters is observed and may be due to active galactic nucleus (AGN) contamination. Corrections for dust attenuation are applied assuming A Hα = 1 mag. We also design our own empirical rest-frame g − r calibration using SDSS DR12 data, test it against our z  = 0.47 H α emitters with z COSMOS 1D spectra, and calibrate it for (g − r) between −0.8 and 1.3 mag. Dust and AGN-corrected star formation rate densities (SFRDs) are measured as log10ρSFR/(M⊙ yr−1 Mpc−3) = −1.63 ± 0.04, −1.07 ± 0.06, and −0.90 ± 0.10 for H α, [O  iii ], and [O  ii ], respectively. We find our [O  iii ] and [O  ii ] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multiwavelength SFRDs, while the H α sample traces ∼70 per cent of the total z  = 0.47 SFRD. [ABSTRACT FROM AUTHOR]