Asymmetric Absorption Profiles around Ly alpha Lyman beta
Asymmetric Absorption Profiles around Ly alpha Lyman beta 2013. Feb 15 Sejong University Hee-Won Lee
Content ¢ ¢ ¢ Quasar Absorption Systems Kramers-Heisenberg Formula Asymmetry in Scattering Cross Section Observational Ramifications Summary
Quasar Absorption Systems ¢ ¢ ¢ Lyman Alpha Forest Lyman Limit System Damped Lyman Alpha System
Lyman alpha forest ¢ ¢ Residual neutral hydrogen component forming a filamentary structure in the intergalactic medium Appears in the absorption profile blueward of Lyman alpha of a background quasar
Damped Lyman Alpha Systems ¢ ¢ ¢ Defined by N_HI>2 X 10^20 cm^-2 Maybe disk component of a galaxy intervening the sightline Contain most neutral hydrogen providing raw material for star formation during the most of the cosmic time from the reionization era. Important probe for cosmic chemical evolution May contain some dust.
Chemical Evolution with DLAs
Voigt Profile ¢ ¢ Convolution of a Gaussian and a Lorentzian The core part is approximately Gaussian whereas the wing part is Lorentzian. Resonance line shape is approximately Lorentzian in the near wing part. Far wing part, deviation from a Lorentzian is observed depending on the atomic wavefunction.
Resonance Scattering in Classical Physics ¢ ¢ An atom is regarded as a simple harmonic oscillator. Scattering of electromagnetic radiation by an atom is analogous to an externally driven simple harmonic oscillator. Lorentzian behavior is universally obtained. Quantum mechanical correction is given in terms of the oscillator strength.
Qunatum Mechanical Description ¢ ¢ ¢ Initial State: Incident Photon+Atom in Ground State Intermediate State : Atom in an excited np state. Final State: Outgoing Photon+Atom in Ground (or Excited) State
Kramers-Heisenberg Formula
Hydrogen Atom ¢ ¢ Admits wavefunctions in an analytically closed form. Electric dipole operator connecting two eigenstates of hydrogen has matrix elements given in terms of confluent hypergeometric function.
Expansion of K-H Formula around Ly Alpha
Expansion of K-H Formula around Ly beta
Exact Cross Section around Ly alpha and beta
Asymmetry around Ly alpha and Ly beta ¢ ¢ Redward asymmetry around Lyman alpha. Blueward asymmetry around Ly beta
Transmission Coefficients
Absorption Center shift
Voigt fit using shifted centers (ly a)
Shifted Voigt function (ly b)
Extreme HI content toward grb ¢ ¢ GRB 080607 N HI=5 X 10 22 cm-2 Inadequecy of Voigt profile fitting Accurate atomic physics is necessary.
Why?
Summary and Discussion ¢ ¢ ¢ Accurate atomic physics is required for careful analysis of DLAs, which are important in study of star formation process. GRBs may provide another aspect of star forming history. Gunn-Peterson troughs should be analyzed using accurate atomic physics.
- Slides: 22
