Outside the Lyman-break box: detecting Lyman continuum emitters at 3.5 < z < 5.1 with CLAUDS

Abstract

Identifying non-contaminated sample of high-redshift galaxies with escaping Lyman continuum (LyC) flux is important for understanding the sources and evolution of cosmic reionization. We present CLAUDS u-band photometry of the COSMOS field to probe LyC radiation from spectroscopically confirmed galaxies at z 3.5 and outside the standard Lyman-break galaxy colour selection expectations. Complementary to the CLAUDS data, we use Subaru multifilter photometry, Hubble Space Telescope (HST) multi-filter imaging, and the spectroscopic surveys D10K, VUDS and 3D-HST. We present a sample of Lyman continuum galaxy (LCG) candidates in the redshift range 3.5 z 5.1. Here, we introduce 5 LCG candidates, where two are flagged quality 1 and three quality 2. The estimated f abs esc for quality 1 candidates are in the range ∼ 5% − 73% and ∼ 30% − 93%. These estimates are based on our derived parameters from individual galaxies as inputs to a range of BPASS models as well as mean intergalactic medium (IGM) and maximal intergalactic and circumgalactic media (IGM+CGM) transmission. We conclude that our search for LCGs is most likely biased to lines of sight with low HI densities or free from Lyman limit systems. Our two best LCG candidates have EW (Lyα) 50Å and we find no correlation or anti-correlation between EW (Lyα), f abs esc , and R obs , the ratio of ionizing to non-ionizing observed flux in the measured passbands. Stacking candidates without solid LyC detections (S/N < 3) results in an estimated f abs esc from galaxies not greater than 1%.

The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

“…In recent years, direct 𝑓 esc studies have largely concentrated on two redshift windows set by available UV instrumentation -one at 𝑧 ≈ 0.3 where Lyman continuum (LyC) is accessible to HST/COS (e.g., Izotov et al 2016aIzotov et al , 2018bIzotov et al , 2021aWang et al 2019Wang et al , 2021, and another at 𝑧 ≈ 2 − 4 accessible to ground-based facilities and HST/WFC3 UVIS (e.g., Jones et al 2018;Smith et al 2020;Ji et al 2020;Meštrić et al 2020;Marques-Chaves et al 2021;Davis et al 2021;Prichard et al 2021). The 𝑧 ≈ 0.3 COS efforts were first undertaken at a time when only a handful of robust LyC leakers had been identified, and it was unclear whether LyC leakage even occurred among the 0.5𝐿 * galaxies for which 𝑓 esc measurements were feasible (e.g., Izotov et al 2016a,b).…”

A Cautionary Tale of LyC Escape Fraction Estimates from High Redshift Galaxies

“…As in previous works (e.g. Bassett et al 2019;Meštrić et al 2020) 𝑢-band data comes from the CFHT Large Area Uband Deep Survey (CLAUDS, Sawicki et al 2019), which reaches a maximum depth of ∼27.2-27.3 mag in the 𝑢-band. We note that the 𝑢-band used here for LyC detections is distinct from the 𝑢 * -band of the ZFOURGE survey.…”

“…The difficulty in definitively answering the question of which sources are primarily responsible for reionization can be attributed to the faintness of these sources (e.g. Bian & Fan 2020;Meštrić et al 2020) and the high opacity of the IGM during the EoR. Based on known samples of Lyman Break Galaxies (Steidel et al 2018, LBGs) and Lyman 𝛼 emitters (LAEs Fletcher et al 2019), Bassett et al (2021) predict that LyC emission from the bulk of star-forming galaxies at 𝑧 ≥ 3.0 should be fainter than 28 mag AB.…”

SDSS-IV MaNGA: an observational evidence of density bounded region in a Lyman-$α$ emitter

“…Nevertheless, both of these systems show a similar specific−SFR (sSFR) lying in the range of 10 −7 − 10 −9 yr −1 . In the literature, several of these GPs and Bluebrries have now been confirmed as Lyman Continuum (LyC) and Lyα leakers showing an escape fraction of ionizing photons in the range of 2 − 72% (Borthakur et al 2014;Jaskot et al 2019;Leitherer et al 2016;Izotov et al 2016aIzotov et al ,b, 2018a, like the high-redshift leaky star-forming galaxies (e.g., Shapley et al 2016;Bian et al 2017;Vanzella et al 2018;Fletcher et al 2019;Meštrić et al 2020;Marques-Chaves et al 2021).…”