Helium Reionization Simulations. III. The Helium Lyα Forest

Fluctuations in the Ionizing Background during and after Helium Reionization

The radiation background above the ionization edge of He II varies strongly during and after helium reionization, because the attenuation length of such photons is relatively short (. 40 Mpc) and because the ionizing sources (quasars) are rare. Here we construct analytic and Monte Carlo models to examine these fluctuations, including, for the first time, those during the reionization era itself...

Lyα/Hα Ratio of Singly Ionized Helium in Quasars

He ii Lyα λ304/Hα λ1640 emission lines are mainly produced by recombination, and their canonical ratio of ∼ 10 may be a sensitive reddening indicator. We obtain the high S/N optical spectra of two quasars and combine them with the far-UV spectra that show the He ii λ304 emission. For HS 1700+64, the He ii λ1640 emission is not detected, and an upper limit to it sets the ratio greater than 20. T...

Reionization of Hydrogen and Helium by Early Stars and Quasars

We compute the reionization histories of hydrogen and helium due to the ionizing radiation fields produced by stars and quasars. For the quasars we use a model based on halo-merger rates that reproduces all known properties of the quasar luminosity function at high redshifts. The less constrained properties of the ionizing radiation produced by stars are modeled with two free parameters: (i) a ...

Surface Impact Simulations of Helium Nanodroplets

HELIUM , SOLID 1 Helium , Solid

Helium was first solidified at the famous Kamerlingh Onnes low-temperature physics laboratories in Leiden by W. H. Keesom [1] on June 25, 1926. The initial experiments by Sir Francis Simon at Oxford University and by Keesom and their collaborators focused on the melting curve, the specific heat, and the thermal conductivity of solid helium as a test of our early understanding of solids. These m...