HST Emission Line Galaxies at z ~ 2: The Ly-alpha Escape Fraction

Abstract

We compare the H-beta line strengths of 1.90 < z < 2.35 star-forming galaxies observed with the near-IR grism of the Hubble Space Telescope with ground-based measurements of Ly-alpha from the HETDEX Pilot Survey and narrow-band imaging. By examining the line ratios of 73 galaxies, we show that most star-forming systems at this epoch have a Ly-alpha escape fraction below ~6%. We confirm this result by using stellar reddening to estimate the effective logarithmic extinction of the H-beta emission line (c_Hbeta = 0.5) and measuring both the H-beta and Ly-alpha luminosity functions in a ~ 100,000 cubic Mpc volume of space. We show that in our redshift window, the volumetric Ly-alpha escape fraction is at most 4.4+/-2.1(1.2)%, with an additional systematic ~25% uncertainty associated with our estimate of extinction. Finally, we demonstrate that the bulk of the epoch's star-forming galaxies have Ly-alpha emission line optical depths that are significantly greater than that for the underlying UV continuum. In our predominantly [O~III] 5007-selected sample of galaxies, resonant scattering must be important for the escape of Ly-alpha photons.

14 pages, 3 figures, Accepted to ApJ

References in corpus (14)

• The Cosmic Evolution Survey (COSMOS) -- Overview
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• Effects of Dust Geometry in Lyman Alpha Galaxies at z = 4.4
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• The Properties of Hα Emission-Line Galaxies at z = 2.24
• 3D-HST Emission Line Galaxies at z ~ 2: Discrepancies in the Optical/UV Star Formation Rates

Cited by in corpus (11)

• The CALYMHA survey: Lya luminosity function and global escape fraction of Lya photons at z=2.23
• A Comprehensive Study of Ly$\alpha$ Emission in the High-redshift Galaxy Population
• The ALMA REBELS Survey: Efficient Ly$\alpha$ Transmission of UV-Bright z$\simeq$7 Galaxies from Large Velocity Offsets and Broad Line Widths
• Ly$\alpha$ Emitters with Very Large Ly$\alpha$ Equivalent Widths, EW${}_0$(Ly$\alpha$) $\simeq 200-400$ Å, at $z\sim 2$
• The cosmic web in Lyman-alpha emission
• The HETDEX Survey: The Ly$\alpha$ Escape Fraction from 3D-HST Emission Line Galaxies at $z\sim 2$
• A survey of Ly$\alpha$ emission around Damped Ly$\alpha$ absorbers at $z\approx 2$ with the Keck Cosmic Web Imager
• NuSTAR hard X-ray data and Gemini 3D spectra reveal powerful AGN and outflow histories in two low-redshift Lyman-$\alpha$ blobs
• Extinction Correction Significantly Influences the Estimate of Ly$\alpha$ Escape Fraction
• The H$\alpha$ and [O III] $\lambda 5007$ Luminosity Functions of $1.2<z<1.9$ Emission-Line Galaxies from HST Grism Spectroscopy
• The $z\sim 2$ $[\mathrm{O}\mathrm{III}]$ Luminosity Function of Grism-selected Emission-line Galaxies