A Lyman Break Galaxy in the Epoch of Reionization from HST Grism Spectroscopy

Abstract

We present observations of a luminous galaxy at redshift z=6.573 --- the end of the reioinization epoch --- which has been spectroscopically confirmed twice. The first spectroscopic confirmation comes from slitless HST ACS grism spectra from the PEARS survey (Probing Evolution And Reionization Spectroscopically), which show a dramatic continuum break in the spectrum at restframe 1216 A wavelength. The second confirmation is done with Keck + DEIMOS. The continuum is not clearly detected with ground-based spectra, but high wavelength resolution enables the Lyman alpha emission line profile to be determined. We compare the line profile to composite line profiles at redshift z=4.5. The Lyman alpha line profile shows no signature of a damping wing attenuation, confirming that the intergalactic gas is ionized at redshift z=6.57. Spectra of Lyman breaks at yet higher redshifts will be possible using comparably deep observations with IR-sensitive grisms, even at redshifts where Lyman alpha is too attenuated by the neutral IGM to be detectable using traditional spectroscopy from the ground.

19 pages, four figures. Resubmitted to The Astrophysical Journal after revisions to address the referee's report

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• The Grism Lens-Amplified Survey from Space (GLASS). I. Survey overview and first data release
• Observational Searches for Galaxies at z > 6
• LAGER Ly$\alpha$ Luminosity Function at $z\sim 7$, Implications for Reionization
• First results from Faint Infrared Grism Survey (FIGS): first simultaneous detection of Lyman-alpha emission and Lyman break from a galaxy at z=7.51
• Discovery of a z = 7.452 High Equivalent Width Lyman-α Emitter from the Hubble Space Telescope Faint Infrared Grism Survey
• CLEAR: Boosted Ly$\alpha$ Transmission of the Intergalactic Medium in UV bright Galaxies
• Evidence for Reduced Specific Star Formation Rates in the Centers of Massive Galaxies at z = 4
• Physical Properties of Local Star-Forming Analogues to z~5 Lyman Break Galaxies
• A Catalog of Emission-Line Galaxies from the Faint Infrared Grism Survey: Studying Environmental Influence on Star Formation
• Radio observations confirm young stellar populations in local analogues to $z\sim 5$ Lyman break galaxies
• Constraints on the Epoch of Reionization with Roman Space Telescope and the Void Probability Function of Lyman-Alpha Emitters