2013. Feb 15 Sejong University Hee-Won Lee Quasar Absorption Systems Kramers-Heisenberg Formula Asymmetry in Scattering Cross Section Observational Ramifications Summary Lyman Alpha Forest Lyman Limit System Damped Lyman Alpha System 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 Defined by N_HI>2X10^20 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. 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. 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. 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 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. Redward asymmetry around Lyman alpha. Blueward asymmetry around Ly beta GRB 080607 N HI=5X10 22 cm-2 Inadequecy of Voigt profile fitting Accurate atomic physics is necessary. 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.