Evidence for a Low Lyman Continuum Escape Fraction in Three Massive, Ultraviolet-bright Galaxies at z > 7

Abstract

Although low-mass star-forming galaxies are the leading candidates of the reionization process, we cannot conclusively rule out high-mass star-forming galaxies as candidates. While most simulations indicate the former is the best candidate, some models suggest that at z ≥ 6 massive, UV-bright galaxies – “oligarchs” – account for at least 80% of the ionizing budget. To test this hypothesis, we target massive ( ${\mathrm{log}}_{10}({\text{}}{M}_{\star }[{\text{}}{M}_{\odot }])\gt 10$ ), UV-bright ( M _UV ∼ −22) Ly α emitters at z > 7 in archival data, observed with similar resolution spectrographs (Very Large Telescope/X-shooter and Keck/MOSFIRE). To increase the reliability of our conclusions, we stack all spectra and obtain a deep-stacked spectrum of 24.75 hr. The stacked Ly α profile displays a clear asymmetric red peak and an absence of a blue peak. We additionally estimate the intrinsic stacked Ly α profile of our targets by correcting for intergalactic medium (IGM) transmission using a range of neutral hydrogen fractions, finding no significant change in the profile. We measure a velocity offset V _red > 300 km s ^−1 and an asymmetry in our red peak A ∼ 3. Using various models and estimators, such as the peak separation, the asymmetry of the red peak, the ratio between Ly α and H β, and the β slope, we conclude that the escape fraction in these three UV-bright, massive (∼10 ^10 M _⊙ ), z ≥ 7 galaxies is f _esc (LyC) ≤ 10%.

Keywords

• Lyman-alpha galaxies
• Reionization
• High-redshift galaxies