Understanding the spatial variation of \ion{Mg}{II} and ionizing photon escape in a local LyC leaker

Abstract

Ionizing photons must have escaped from high-redshift galaxies, but the neutral high-redshift intergalactic medium makes it unlikely to directly detect these photons during the Epoch of Reionization. Indirect methods of studying ionizing photon escape fractions present a way to infer how the first galaxies may have reionized the universe. Here, we use HET/LRS2 observations of J0919+4906, a confirmed z$\approx$0.4 emitter of ionizing photons to achieve spatially resolved (12.5 kpc in diameter) spectroscopy of \ion{Mg}{II}$\lambda 2796$, \ion{Mg}{II}$\lambda 2803$, [\ion{O}{II}]$\lambda \lambda 3727,3729$ , [\ion{Ne}{III}]$\lambda 3869$, H$\gamma$, [\ion{O}{III}]$\lambda 4363$, H$\beta$, [\ion{O}{III}]$\lambda 4959$, [\ion{O}{III}]$\lambda 5007$, and H$\alpha$. From these data we measure \ion{Mg}{II} emission, which is a promising indirect tracer of ionizing photons, along with nebular ionization and dust attenuation in multiple spatially-resolved apertures. We find that J0919+4906 has significant spatial variation in its \ion{Mg}{II} escape and thus ionizing photon escape fraction. Combining our observations with photoionization models, we find that the regions with the largest relative \ion{Mg}{II} emission and \ion{Mg}{II} escape fractions have the highest ionization and lowest dust attenuation. Some regions have an escape fraction that matches that required by models to reionize the early universe, while other regions do not. We observe a factor of 36 spatial variation in the inferred LyC escape fraction, which is similar to recently observed statistical samples of indirect tracers of ionizing photon escape fractions. These observations suggest that spatial variations in neutral gas properties lead to large variations in the measured LyC escape fractions. Our results suggest that single sightline observations may not trace the volume-averaged escape fraction of ionizing photons.

12 pages, 7 figures

References in corpus (25)

• Array Programming with NumPy
• Cosmic Star Formation History
• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: I. Galaxy Mergers & Quasar Activity
• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• Conditions for Reionizing the Universe with A Low Galaxy Ionizing Photon Escape Fraction
• Using Lyman-alpha to detect galaxies that leak Lyman continuum
• A Local Clue to the Reionization of the Universe
• The Low-Redshift Lyman Continuum Survey I: New, Diverse Local Lyman-Continuum Emitters
• Q1549-C25: A Clean Source of Lyman-Continuum Emission at $z=3.15$
• The Low-Redshift Lyman Continuum Survey II: New Insights into LyC Diagnostics
• The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization
• Lyman continuum leakage from low-mass galaxies with Mstar < 1.E8 Msun
• The Sunburst Arc: Direct Lyman α escape observed in the brightest known lensed galaxy
• Optically-Thin Spatially-Resolved Mg II Emission Maps the Escape of Ionizing Photons
• The Low-Redshift Lyman Continuum Survey. Unveiling the ISM properties of low-$z$ Lyman continuum emitters
• Constraining the UV emissivity of AGN throughout cosmic time via X-ray surveys
• (Re)Solving Reionization with Lyα: How Bright Lyα Emitters account for the $z\approx 2-8$ Cosmic Ionizing Background
• Minor Contribution of Quasars to Ionizing Photon Budget at z~6: Update on Quasar Luminosity Function at the Faint-end with Subaru/Suprime-Cam
• Strong Lyman continuum emitting galaxies show intense CIV 1550 emission
• UV absorption lines and their potential for tracing the Lyman continuum escape fraction
• Assessing the sources of reionisation: a spectroscopic case study of a 30$\times$ lensed galaxy at $z\sim 5$ with Lyα, CIV, MgII, and [NeIII]
• Tracing Lyman-alpha and Lyman Continuum Escape in Galaxies with Mg II Emission
• Lyman alpha and Lyman continuum emission of MgII-selected star-forming galaxies
• Inferring the properties of the sources of reionization using the morphological spectra of the ionized regions

Cited by in corpus (2)

• The Low-Redshift Lyman Continuum Survey: Optically Thin and Thick Mg II Lines as Probes of Lyman Continuum Escape
• Spectroscopy of CASSOWARY gravitationally-lensed galaxies in SDSS: characterisation of an extremely bright reionization-era analog at $z=1.42$