1. Evolution of the Keri Dixon University of California, Los Angeles Steven Furlanetto Reionization @ Ringberg 25.03.2009 He-ionizing background

2. 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

3. Begin with  He II HE 2347-4342: Zheng et al. 2004, Shull et al. 2004, Kriss et al. 2001 HS 1700+64: Fechner et al. 2006, Davidsen et al. 1996 Q0302-003: Heap et al. 2000, Hogan et al. 1997 HS 1157+3143: Reimers et al. 2005 PKS 1935-692: Anderson et al. 1996

4. 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. 2000 Assume isothermal equation of state

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

6. 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

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

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

9. Where’s reionization?

10. 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

11. Including T-dependence