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We have run a new suite of simulations that solve hydrodynamics and radiativetransfer simultaneously to study helium II reionization. Our suite ofsimulations employs various models for populating quasars inside of dark matterhalos, which affect the He II reionization history. In particular, we are ableto explore the impact that differences in the timing and duration ofreionization have on observables. We examine the thermal signature thatreionization leaves on the IGM, and measure the temperature-density relation.As previous studies have shown, we confirm that the photoheating feedback fromhelium II reionization raises the temperature of the IGM by several thousandkelvin. To compare against observations, we generate synthetic Ly$\alpha$forest sightlines on-the-fly and match the observed effective optical depth$\tau_{\mathrm{eff}}(z)$ of hydrogen to recent observations. We show that whenthe simulations have been normalized to have the same values of$\tau_\mathrm{eff}$, the effect that helium II reionization has on observationsof the hydrogen Ly$\alpha$ forest is minimal. Specifically, the flux PDF andthe one-dimensional power spectrum are sensitive to the thermal state of theIGM, but do not show direct evidence for the ionization state of helium. Weshow that the peak temperature of the IGM typically corresponds to the time of90%-95% helium ionization by volume, and is a relatively robust indicator ofthe timing of reionization. Future observations of helium reionization from thehydrogen Ly$\alpha$ forest should thus focus on measuring the temperature ofthe IGM, especially at mean density. Detecting the peak in the IGM temperaturewould provide valuable information about the timing of the end of helium IIreionization.

Helium Reionization Simulations. II. Signatures of Quasar Activity on the IGM