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

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

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

What do we expect to see?

He II reionization “footprint”: the temperature evolution z 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

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 He II reionizazion flattening

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

What was found?

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

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

 < 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 Blazar heating models photo-heating model Low-redshift region

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

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

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

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 Δ= 1 Δ > > Maintains degeneracy between T 0 &  

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

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

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

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

Data sample C/N>24

Data analysis 10h -1 Mpc

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

Data analysis: curvature results

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

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

Simulation analysis: curvature results

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

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

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

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

Results: IGM temperature at the mean density

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

THANKS !

Metal correction

Metal correction: curvature