docThe Escape Fraction in the Epoch of Reionisation
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The Escape Fraction in the Epoch of Reionisation
The Escape Fraction in the Epoch of Reionisation Jan-Pieter Paardekooper ! Sadegh Khochfar Claudio Dalla Vecchia ! TMoX Group Max Planck Institute for Extraterrestrial Physics Image credit: Claudio Dalla Vecchia Outline ! What were the sources of reionisation? ! ! ! What is the physical driver of the escape fraction? ! ! ! What can we learn about reionisation? Reionisation sources FiBY Absorption Escape Fraction Conclusions 2 −1 "−12 1+z 7 −1 −12 αs αb + 3 λmfp Galaxies as reionisers 3 6 40 Mpc "−2 s−1 Mpc−3 , (21) error in our estimate of the mean free path. emissivity inferred from the&Lyα opacity is n Bolton Haehnelt (2007) redshift range 2 ! z ! 6. Assuming a spec above the Lyman limit, it is well character servational constraints on the emission rate of ionizing photons per comoving Mpc, Ṅion , as a function of redshift. = α b = 3 and,Reionisation in the casesources of the LBG and emissivity estimates only, f esc = 0.2. TheConclusions scale on the right-hand v FiBYLyα emitter Absorption Escape Fraction ionizing photons emitted per hydrogen atom over the Hubble time at z = 6. The filled triangles give an estimate of Ṅi Galaxies as reionisers Robertson et al (2013) Figure 2. Constrained ultraviolet (UV) luminosity densities ρUV as a function of limiting magnitude MUV and redshift z. Shown are the z ∼ 5–8 maximum likelihood values of ρUV vs. limiting magnitude calculated using Equation (5) (white lines), and the corresponding marginalized inner 68% credibility intervals for ρUV (MUV ) Reionisation FiBY Escape Fraction Also shown is the ρUVConclusions (blue regions).sources In each panel, we indicate with a dotted lineAbsorption the limiting depth of the luminosity function determinations. required for galaxies −1 to maintain a fully ionized universe assuming log ξion = 25.2 log erg Hz, fesc = 0.2, CH ii = 3, and case A recombination (dashed lines and gray regions). We use Bayesian parameter estimation methods to determine the Schechter (1976) function parameter posterior distributions inferred from the stepwise maximum likelihood luminosity function (LF) data of Bouwens et al. (2007) at z ∼ 4–6 and McLure et al. (2012) at z ∼ 7–8. We also use the full posterior distribution sampling of the Escape fraction simulations Reionisation sources FiBY Absorption JPP, Pelupessy, Altay & Kruip (2011) Escape Fraction Conclusions Escape fraction simulations Reionisation sources FiBY Absorption JPP, Pelupessy, Altay & Kruip (2011) Escape Fraction Conclusions FiBY simulation First Billion Years project ! Gadget2 (OWLS) ! Pop III + Pop II ! Thermal SN feedback ! 11 species line cooling ! Molecular cooling ! Uniform UV background builds up 9 < z < 12 Lbox 4 Mpc 8 Mpc Npart 2 ⇥ 6843 2 ⇥ 13683 Mg,part 1250 M Reionisation sources FiBY Khochfar et al. in prep Dalla Vecchia et al. in prep 1250 M Absorption Escape Fraction Conclusions Halo sample Select all haloes with at least 1 star particle and 1000 dm particles ! ! 4 Mpc box: > 11,000 haloes in redshift range 6 < z < 22 ! 8 Mpc box: > 64,000 haloes in redshift range 9 < z < 27 ! number of star particles in each halo: few - >140,000 ! ! Determine the fraction of produced photons that reach virial radius Nphot (r > r200 , t) fesc (t) = Nemitted (t) Reionisation sources FiBY Absorption Escape Fraction Conclusions Radiative transfer JPP, Kruip & Icke 2010 ! ! ! ! Radiative transfer in post-processing ! ! Follow photons from Pop III and Pop II stars ! ! Spectra from stellar synthesis models (Raiter et al. 2010; Leitherer et al 1999) ! ! Absorption by hydrogen and helium ! ! Multi-frequency approach including relevant heating and cooling processes ! Reionisation sources FiBY Absorption Escape Fraction Conclusions Proto-galaxies as reionisers Reionisation sources FiBY Absorption JPP, Khochfar & Dalla Vecchia 2013 Escape Fraction Conclusions Proto-galaxies as reionisers Reionisation sources FiBY Absorption JPP, Khochfar & Dalla Vecchia (2013) Escape Fraction Conclusions Absorption ! ! ! ! Where are the ionising photons absorbed? ! Absorption scales with n2H ! (r<10 pc) NH Reionisation sources FiBY = P (r<10 pc) Nion,i i NH,i P Absorption i Nion,i Escape Fraction Conclusions Column density Reionisation sources FiBY Absorption Escape Fraction Conclusions Active haloes Reionisation sources FiBY Absorption Escape Fraction Conclusions Column density Reionisation sources FiBY Absorption Escape Fraction Conclusions Virial mass Reionisation sources FiBY Absorption Escape Fraction Conclusions Probability Reionisation sources FiBY Absorption Escape Fraction Conclusions Scatter Reionisation sources FiBY Absorption Escape Fraction Conclusions UV background Reionisation sources FiBY Absorption Escape Fraction Conclusions UV background Reionisation sources FiBY Absorption Escape Fraction Conclusions Conclusions To understand the sources of cosmic reionisation we need large samples ! ! THE escape fraction does not exist ! ! The amount and distribution of dense gas determines the escape fraction ! ! Escape of ionising radiation is highly inhomogeneous ! ! Mass dependence of escape fraction points towards low-mass haloes ! ! Ionising feedback is essential Reionisation sources FiBY Absorption Escape Fraction Conclusions
