1. Michael Murphy Elisa Boera Collaborators: Supervisor : G. Becker J. Bolton

2. Outline The post- He II reionization IGM : the “footprint” of photo-heating Previous results: uncertainties and new hypothesis Applying the curvature method at low redshifts: what we need Results: Temperature and heating models

3. The He II reionization impact on the IGM HeII HeIII e-e- γ I = 54.4 eV The electron will share its energy with the baryons E γ > 54.4eV E e- =E γ - I Photo - heating

4. What do we expect to see?

5. He II reionization “footprint”: the temperature evolution z 5 0 12 34 5 10 15 T 0 /10 3 K T at the mean density No reionizazion model He II reionizazion “model” He II reionization mark: a peak at redshift z~3 followed by rapid cooling due to adiabatic expansion

6. He II reionization “footprint”: the T-  relation T( Δ ) = T 0 Δ γ -1  Δ =  Gas overdensi ties Temperature at the mean density Slope power- law z γ 0 0 12 3 4 5 1 1.6 He II reionizazion flattening

7. Why it is important to constrain the thermal history of the low redshift IGM ? To test predictions To constrain the He II reionization To study ionising sources To study the chemical & thermodynamic conditions for structures formation

8. What was found?

9. Previous Results T0 T0 Schaye et al. 2000: Line fitting Lidz et al. 2009: wavelet analysis Garzilli et al. 2012: wavelet + PDF

10. Previous Results Schaye et al. 2000 Ricotti et al. 2000 line fitting  PDF  at z < 3 Becker et al. 2007 Bolton et al 2008, Viel et al. 2009, Calura et al. 2012, Garzilli et al. 2012

11.  < 1 T( Δ ) = T 0 Δ γ -1<0 Lower density regions show higher temperature Chang et al. 2011: NEW VOLUMETRIC HEATING FROM BLAZAR TeV EMISSION Puchwein et al. 2012 Blazar heating models photo-heating model Low-redshift region

12. What is the thermal state of the IGM at low redshift (z< 3) and which are the possible heating processes that could explain it ?

13. The curvature statistic Simple to compute Systematic uncertainties minimized ✔ ✔ κ = F [1+( F ) 2 ] 3/2 Derivatives of the flux Becker et al. 2011

14. The overall amplitude of the curvature is greater at the lower temperature Sensitive to the IGM temperature ✔

15. Hydrodynamical simulation T( Δ ) Overdensities traced by the Ly- α forest  ) The Ly- α forest not always traces the gas at the mean density (  ) BUT… Becker et al. 2011 Δ= 1 Δ > > Maintains degeneracy between T 0 &  

16. The curvature statistic T( Δ ) T0T0 T( Δ ) = T 0 Δ γ -1 We need to constrain  ! Degeneracy

17. Previous curvature results with the curvature statistic Becker et al. 2011 Gradual reheating Evidence for the peak of He II reionization very tenuous New measurements needed at lower redshift z < 2.0 T( Δ )

18. General plan of the project Data preparation T( Δ ) T0T0 Simulation by J. Bolton

19. Data analysis: preparation of the data 60 spectra high S/N  L   UVES archive selection C/N>24

20. Data sample C/N>24

21. Data analysis 10h -1 Mpc

22. Data analysis: curvature measurements b – spline fit Mean absolute curvature Mean flux

23. Data analysis: curvature results

24. General plan of the project Data preparation T( Δ ) T0T0 Simulation by J. Bolton

25. Simulation analysis Synthetic spectra in the same z range of the data Hydrodynamical simulations (GADGET 3) Box size: 10 h -1 Mpc 2*512 3 particles Different T 0 &  Different thermal histories Instrumental resolution Optical depth noise

26. Simulation analysis: curvature results

27. General plan of the project Data preparation T( Δ ) T0T0 Simulation by J. Bolton

28. Final analysis T( Δ ) Simulations Interpolation of the T(  )-log with the data values Empirical search for T( Δ ) at each z

29. Results: IGM temperature at the characteristic overdensities The results overlap Possible dip

30. General plan of the project Data preparation T( Δ ) T0T0 Simulation by J. Bolton T( Δ ) = T 0 Δ γ -1

31. Results: IGM temperature at the mean density

32. Summary We obtained measurements of the temperature at the lowest possible optical redshifts The results do not seem favor strongly any blazar heating model but there is still degeneracy between T 0 and  Not strong statistical evidence for a structure at low redshift for T( Δ ) No clear evidence for a peak due to He II reionization

33. THANKS !

34. Metal correction

35. Metal correction: curvature