Evolution of the Keri Dixon University of California, Los Angeles Steven Furlanetto Ringberg He-ionizing background

Looking for the photoionization rate Assume background ionization flux: The attenuation length R 0 is treated as an unknown. When convenient, choose The emissivity  is also uncertain. Bolton et al. 2006

Begin with  He II HE : Zheng et al. 2004, Shull et al. 2004, Kriss et al HS : Fechner et al. 2006, Davidsen et al Q : Heap et al. 2000, Hogan et al HS : Reimers et al PKS : Anderson et al. 1996

From  eff to  Start with the Gunn-Peterson optical depth Balance photoionization and recombination for HeII Introduce the fractional density of the IGM (  ) with p(  ) Miralda-Escudé et al Assume isothermal equation of state

Fluctuating vs. Uniform Helium reionization driven by quasars  fluctuating  Uniform ~ R 0 = ∞ The attenuation length and ionized fraction affect distribution. Furlanetto 08

Evolution of  Pin to curve at z = 2.45 Uncertain (mainly) due to limited lines of sight Significant departure from curve z ~ 2.75 (?) Choose convenient R 0

Evolution of R 0 Pin to curve at z = 2.45 Fluctuating background smoothes evolution Significant jump z ~ 2.75 (?) Choose convenient 

What do we see? Assume convenient  Data could distinguish the three regimes Find expected  eff Choose convenient R 0

Where’s reionization?

Time for lunch…just kidding It seems like probably something is happening around z ~ 2.75 Possible conclusions: Reionization is happening near this redshift This “something” does not indicate reionization The model is an insufficient approximation

Including T-dependence