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Escape of Ionizing Radiation From Galaxies

Escape of Ionizing Radiation From Galaxies. Nick Gnedin. Co-starring. Andrey Kravtsov. Hsiao-Wen Chen. Outline. Simulating escape, and what it actually means. Cosmologist’s bane, and how it affects escape fractions. Escaping from simulations.

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Escape of Ionizing Radiation From Galaxies

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  1. Escape of Ionizing Radiation From Galaxies Nick Gnedin

  2. Co-starring Andrey Kravtsov Hsiao-Wen Chen

  3. Outline • Simulating escape, and what it actually means. • Cosmologist’s bane, and how it affects escape fractions. • Escaping from simulations. • Does it all make sense – or, who is fatter in the world of galaxies? • Conclusions.

  4. Simulating Escape • Adaptive Refinement Tree (ART) code. • A Milky Way type progenitor in a 6 CHIMP box. • Spatial resolution ~50 pc @ z~3. • Stars form only in gas with nH>50 cm-3 with rate consistent with Krumholts & McKee 2005, Krumholts & Tan 2007. • Optically Thin Variable Eddington Tensor (OTVET) approximation is used for modeling Radiative Transfer. • Non-equilibrium ionization balance and cooling function are computed “on the fly”.

  5. Lyman-limit systems Dark matter halo Escaping radiation Measuring Escape Fraction

  6. Many Faces of fesc • Integrate over angles: angular-averagedfesc(n). • Integrate over frequencies: escape fraction of ionizing radiation. • A number = angular-averaged escape fraction of ionizing radiation. • Know your escape fraction!

  7. A View from the Source fESC @ D = 1.0 RVIR (100 h-1 kpc, 0.0012 lLL) @ D = 2.0 RVIR (200 h-1 kpc, 0.0025 lLL) @ D = 5.0 RVIR (500 h-1 kpc, 0.005 lLL) @ D = 10 RVIR (1 h-1 Mpc, 0.01 lLL) @ D = 30 RVIR (3 h-1 Mpc, 0.03 lLL) @ D = 100 RVIR (10 h-1 Mpc, 0.1 lLL) @ D = 0.5 RVIR (50 h-1 kpc, 0.0006 lLL)

  8. Cosmologist’s Bane: Dust • Assume: dust-to-gas ratio scales with metallicity. Two models: • Instant sublimation • No sublimation • Use Pei (1992) parameterization. • Adjust Pei’s parameters to reproduce Weingartner & Draine (2001).

  9. Various Dust Models No dust SMC-IS LMC-IS SMC-NS SMC-IS x 3

  10. Absolute fesc Relative fesc Absolute & Relative fesc

  11. Hydrogen absorbs all anyway Even hydrogen cannot absorb Why Dust Does Not Matter?

  12. Why Dust Does Not Matter?Cartoon Version “Fog” model “Cave” model

  13. Escape Fractions in Galaxies

  14. Escape Fractions in Galaxies

  15. Redshift Evolution

  16. Consistent with fesc in GRB hosts. Model vs Data Correction from relative to absolute fesc.

  17. How Radiation Escapes • Dwarf galaxy • Large galaxy • In large galaxies only radiation from young stars that find themselves near or outside the edge of HI disk can escape. • In dwarf galaxies HI disks are much thicker than stellar disks, so no radiation escapes.

  18. IC2233 UGC7321 Are Real Dwarfs HI-fat?

  19. Are Real Dwarfs HI-fat? Galaxy IC2233 UGC7321Dynamical mass 9.5x109 M83.2x109 M8Stellar disk height 240 pc 150 pcHI disk height 800 pc 580 pc (Matthews & Wood 2003; Matthew & Uson 2008)

  20. Conclusions • Ionizing radiation escapes from galaxies in a “cave”-like mode: some of the young stars get exposed to the exterior of the HI disk due to • waves on the surface of the HI disk; • their own peculiar motions. • That results if a few % angular averaged escape fractions, and a factor of 10 variation in any given direction. • In dwarf galaxies (M < 1011 M8, SFR < 1 M8/yr) HI disks are way too fat for that to happen, their escape fractions are negligible. • Because of “cave”-like mode of radiation escape, dust has little impact on the values of escape fractions.

  21. The End

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