HST/COS Observations of Thirteen New He II Quasars

Abstract

The full reionization of intergalactic helium was a major event in the history of the IGM, and UV observations of the He II Gunn-Peterson trough allow us to characterize the end of this process at z~3. Due to intervening hydrogen absorption, quasars allowing such study are rare, with only 33 known in the literature, and most of those are very recent discoveries. We expand on our previous discovery work, and present 13 new He II quasars with redshifts 2.82 < z < 3.77, here selected with ~80% efficiency, and including several that are much brighter than the vast majority of those previously known. This is the largest sample of uniformly observed He II quasars covering such a broad redshift range, and they show evidence of IGM opacity increasing with redshift, as expected for the helium reionization epoch. No evidence of He II Lyα quasar emission is seen in individual or averaged spectra, posing a problem for standard models of the broad line region. The current rapid advance in the study of He II quasars has been greatly facilitated by the Cosmic Origins Spectrograph on HST, and we discuss the instrumental and other subtleties that must be taken into account in IGM He II observations.

AJ accepted; 14 pages, 7 figures

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• Early and Extended Helium Reionization Over More Than 600 Million Years of Cosmic Time
• The imprint of inhomogeneous HeII reionization on the HI and HeII Ly-alpha forest
• A New Method to Directly Measure the Jeans Scale of the Intergalactic Medium Using Close Quasar Pairs
• Statistical Detection of the HeII Transverse Proximity Effect: Evidence for Sustained Quasar Activity for $>$25 Million Years
• On the Significance of Absorption Features in HST/COS Data
• Constraining the era of helium reionization using fast radio bursts
• The Evolution of the HeII-Ionizing Background at Redshifts 2.3<z<3.8 Inferred from a Statistical Sample of 24 HST/COS HeII Ly$\alpha$ Absorption Spectra
• Helium Reionization Simulations. II. Signatures of Quasar Activity on the IGM
• He II Proximity Effect and the Lifetime of Quasars
• Evidence for Short $\sim 1$ Myr Lifetimes from the He II Proximity Zones of $z\sim 4$ Quasars
• AGN-driven helium reionization and the incidence of extended HeIII regions at redshift z>3
• The He II Post-Reionization Epoch: HST/COS Observations of the Quasar HS1700+6416
• The Effect of Fluctuations on the Helium-Ionizing Background
• A self-consistent 3D model of fluctuations in the helium-ionizing background
• Fast Radio Burst Dispersion Measure Distribution as a Probe of Helium Reionization
• The Escape Fraction of Ionizing Radiation from Galaxies
• New Evidence for Extended HeII Reionization at z>3.5 from HeII Lyman Alpha and Beta Transmission Spikes
• The Thermal Proximity Effect: A New Probe of He II Reionization History and the Quasar Lifetime
• Dating individual quasars with the HeII proximity effect
• Searching for FUV line emission from $10^7$ K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities
• Helium Reionization Simulations. III. The Helium Lyman-$\alpha$ Forest
• Semi-numeric simulations of helium reionization and the fluctuating radiation background
• Probing helium reionization with kinetic Sunyaev Zel'dovich tomography
• Cosmological probes of helium reionization
• HeII Ly$\alpha$ Transmission Spikes and Absorption Troughs in Eight High-resolution Spectra Probing the End of HeII Reionization
• Reconstructing patchy helium reionization using the cosmic microwave background and large-scale structure