Lyman continuum observations across cosmic time: recent developments, future requirements

Abstract

Quantifying the physical conditions that allow radiation emitted shortward of the hydrogen ionization edge at 911.7 Å to escape the first collapsed objects and ultimately reionize the universe is a compelling problem for astrophysics. The escape of LyC emission from star-forming galaxies and AGN is intimately tied to the emergence and sustenance of the metagalactic ionizing background that pervades the universe to the present day and in turn is tied to the emergence of structure at all epochs. JWST was built in part to search for the source(s) responsible for reionization, but it cannot observe LyC escape directly, because of the progressive increase in the mean transmission of the intergalactic medium towards the epoch of reionization. Remarkable progress has been made to date in directly detecting LyC leaking from star-forming galaxies using space-based and the ground-based observatories, but there remain significant gaps in our redshift coverage of the phenomenon. Ongoing projects to measure LyC escape at low- and intermediate-z will provide guidance to JWST investigations by analyzing the robustness of a set of proposed LyC escape proxies, and also provide a closeup examination of the physical conditions that favor LyC escape. However, currently available facilities are inadequate for deeply probing LyC escape at the faint end of the galaxy luminosity function. Doing so will require facilities that can detect LyC emission in the restframe to limiting magnitudes approaching 28 $<m_{(1+z)900}^{\ast }<$ 32 for $M_{(1+z)1500}^{\ast }$ galaxies. The goal of acquiring statistically robust samples for determining LyC luminosity functions across cosmic time will require multi-object spectroscopy from spacebased flagship class and groundbased ELT class telescopes along with ancillary panchromatic imaging and spectroscopy spanning the far-UV to the mid-IR.

Astro2020 submission to Galaxies Evolution, and Cosmology and Fundamental Physics. Cover plus 5 pages plus refs

References in corpus (30)

• An updated analytic model for the attenuation by the intergalactic medium
• Reionization after Planck: The Derived Growth of the Cosmic Ionizing Emissivity now matches the Growth of the Galaxy UV Luminosity Density
• Directly Observing the Galaxies Likely Responsible for Reionization
• Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies
• Low-redshift Lyman continuum leaking galaxies with high [OIII]/[OII] ratios
• J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons
• The GALEX-VVDS Measurement of the Evolution of the 1500A Luminosity Function
• A Local Clue to the Reionization of the Universe
• The Lyman Continuum Escape Survey: Ionizing Radiation from [O III]-Strong Sources at a Redshift of 3.1
• Direct Lyman continuum and Lyman-alpha escape observed at redshift 4
• Consistent modelling of the meta-galactic UV background and the thermal/ionization history of the intergalactic medium
• Q1549-C25: A Clean Source of Lyman-Continuum Emission at $z=3.15$
• A Refined Estimate of the Ionizing Emissivity from Galaxies at z~3: Spectroscopic Follow-up in the SSA22a Field
• The LyA-LyC Connection: Evidence for an Enhanced Contribution of UV-faint Galaxies to Cosmic Reionization
• Direct Detection of Lyman Continuum Escape from Local Starburst Galaxies with the Cosmic Origins Spectrograph
• The Lyman alpha Reference Sample: II. HST imaging results, integrated properties and trends
• Cosmic reionization after Planck
• A Window On The Earliest Star Formation: Extreme Photoionization Conditions of a High-Ionization, Low-Metallicity Lensed Galaxy at z~2
• X-ray binaries as the origin of nebular HeII emission in low-metallicity star-forming galaxies
• The redshift evolution of escape fraction of hydrogen ionizing photons from galaxies
• Local Lyman Break Galaxy Analogs: The Impact of Massive Star-forming Clumps on the Interstellar Medium and the Global Structure of Young, Forming Galaxies
• The photoheating of the intergalactic medium in synthesis models of the UV background
• Galactic porosity and a star formation threshold for the escape of ionising radiation from galaxies
• Photon underproduction crisis: Are QSOs sufficient to resolve it?
• Escape of Lyman-alpha and continuum photons from star-forming galaxies
• Quantifying Distributions of Lyman Continuum Escape Fraction
• Intergalactic Lyman continuum photon budget in the past 5 billion years
• Winds of change: reionization by starburst galaxies
• Lyman `bump' galaxies - II. A possible signature of massive extremely metal-poor or metal-free stars in z=3.1 Ly-alpha emitters
• Characterization and modeling of contamination for Lyman break galaxy samples at high redshift