Opened 4 years ago

#257 new enhancement

treatment of scattering around H I Lyman lines

Reported by: Gary J. Ferland Owned by: nobody
Priority: good to do Milestone:
Component: radiative transfer Version: trunk
Keywords: Cc:


Asymmetric Absorption Profiles of Ly? and Ly? in Damped Lyman Alpha Systems

Hee-Won Lee
(Submitted on 2 Jun 2013)
Damped Ly\alpha\ systems (DLAs) observed in the quasar spectra are characterized by a 
high neutral hydrogen column density $N_{HI}>2\times 10^{20}{\
m\ cm^{-2}}$. The 
absorption wing profiles are often fitted using the Voigt function due to the fact that the 
scattering cross section near resonant line center is approximately described by the 
Lorentzian function. Since a hydrogen atom has infinitely many $p$ states that participate
 in the electric dipole interaction, the cross section starts to deviate from the Lorentzian in 
an asymmetric way in the line wing regions. We investigate this asymmetry in the 
absorption line profiles around Ly\alpha\ and Ly\beta\ as a function of the neutral 
hydrogen column density $N_{HI}$. In terms of $\Delta\lambda\equiv\lambda-
\lambda_\alpha$ we expand the Kramers-Heisenberg formula around Ly\alpha\ to find 
$\sigma(\lambda)\simeq (0.5 f_{12})^2\sigma_{T}(\Delta\lambda/\lambda_\alpha)^{-2}
[1+3.792 (\Delta\lambda/\lambda_\alpha)]$, where $f_{12}$ and $\sigma_T$ are the 
oscillator strength of Ly$\alpha$ and the Thomson scattering cross section, respectively. In
 terms of $\Delta\lambda_2\equiv\lambda-\lambda_\beta$ in the vicinity of Ly\beta, the 
total scattering cross section, given as the sum of cross sections for Rayleigh and Raman 
scattering, is shown to be $\sigma(\lambda)\simeq \sigma_T(0.5f_{13})^2(1+R_0) 
(\Delta\lambda_2/\lambda_\beta)^{-2}[1-24.68(\Delta\lambda_2/\lambda_\beta)]$ with 
$f_{13}$ and the factor $R_0=0.1342$ being the oscillator strength for Ly\beta\ and the 
ratio of Raman cross section to Rayleigh cross section, respectively. A redward asymmetry 
develops around Ly\alpha\ whereas a blue asymmetry is obtained for Ly\beta. The 
absorption center shifts are found to be almost proportional to the neutral hydrogen 
column density.

Comments:	30 pages, 8 figures, 3 tables, accpeted for publication in ApJ
Subjects:	Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as:	arXiv:1306.0181 [astro-ph.CO]
 	(or arXiv:1306.0181v1 [astro-ph.CO] for this version)

Submission history
From: Hee-Won Lee [view email] 
[v1] Sun, 2 Jun 2013 07:37:59 GMT (69kb)

Change History (0)

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