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“The Stromgren sphere” around the highest redshift QSOs

“The Stromgren sphere” around the highest redshift QSOs. Qingjuan Yu UC Berkeley April 7, 2005. Highest redshift QSOs (z>6.1). Gunn-Peterson absorption troughs Hydrogen in the early universe significantly neutral (>1% in mass average)

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“The Stromgren sphere” around the highest redshift QSOs

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  1. “The Stromgren sphere” around the highest redshift QSOs Qingjuan Yu UC Berkeley April 7, 2005

  2. Highest redshift QSOs (z>6.1) • Gunn-Peterson absorption troughs • Hydrogen in the early universe significantly neutral (>1% in mass average) • Flux transmission between the absorption trough and the Ly line center: • Hydrogen in the vicinity of the QSO highly ionized • Highly ionized region idealized as spherical (Stromgren sphere, stellar astronomy) (Fan et al. 2004)

  3. D Apparent shape of the Stromgren sphere • May not be a sphere • Ionization front relativistically expanding • Time-delay effect • rotationally symmetric along OC • r decreases with increasing theta Light reaches the observer at the same moment. (Yu, astro-ph/0411097, ApJ in press)

  4. Apparent shape of the Stromgren sphere Apparent shape of a relativistically expanding radio shell with vel. v: Comparison on geometry (Rees, 1967, MNRAS; Studies in radio source structure: I. A relativistically expanding model for variable quasi-stellar radio sources)

  5. Proper distance: |OC| ~ 5 Mpc ~ 7 arcmin Spectra of background sources (e.g., Ly emitters) Tomography of 21 cm HI emission Possible observational tests

  6. Apparent shapes may be used to constrain: • QSO intrinsic properties: age, luminosity evolution • QSO environment, re-ionization history • clumping factor C • neutral hydrogen fraction • Cosmological parameter:  (Alcock-Paczynski test)

  7. Apparent shapes may be used to constrain: • QSO age

  8. Evolution of the ionization front r for for (Hubble expansion ignored) (Yu & Lu 2005)

  9. QSO age increases from inward to outward. r(=10rec)/(crec)= 4, 8 (left, right). Constraining QSO intrinsic properties and environment Shape evolution

  10. Study of the environment and re-ionization around the highest redshift QSOs: x(HI)~0.1, C~35; • recombination timescale << QSO lifetime (>4x107 yr). The observational Stromgren radii along the line of sight are consistent the expected sizes rS. (Yu & Lu 2005)

  11. re-ionization: C=35, x(HI)=0.1,Q>> rec C=1,x(HI)=1 x(HI)=0.3 x(HI)=0.1 Constraining QSO intrinsic properties and environment

  12. Constraining  (Alcock-Paczynski test) • |OC|, redshift difference • affected little by  at high redshift. • R=dA, Angular diameter distance: • depends on 

  13. 1) Obscuration by a torus (analogous to the [OIII] ionization cone observed in nearby Seyfert II galaxies) 2) Disk emission e.g.,  1+2|| (limb-darkening effect) different cross sections Anisotropic emission

  14. Time-delay effects Decreasing r with increasing theta Anisotropic effects (QSO emission and structure perturbations) May depend on the detailed geometric configuration between the disk and observer; Dominated if the QSO age is significantly long compared to the hydrogen recombination process and the QSO luminosity evolution is significantly slow; Could be statistically averaged out in a large sample. Comparison

  15. Summary • The apparent shape of the ionization fronts around the highest redshift QSOs may systematically deviate from a spherical shape because of the time-delay effect. • The apparent shape of the Stromgren sphere may be mapped by transmitted spectra of background sources behind or inside the ionized regions or by surveys of the hyperfine transition (21 cm) line emission of neutral hydrogen. • Measurements of the apparent shapes may be used to constrain the QSO intrinsic properties and environment (e.g., the re-ionization history of the universe). • The apparent shape could also be used to constrain the cosmological parameter  by the Alcock-Pacynski test if the QSO intrinsic properties and environment are well constrained.

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