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03 October 2022
 
  » arxiv » astro-ph/9701054

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Lyman alpha absorption lines from mini pancakes
Biman B. Nath ;
Date 10 Dec 1996
Journal Astrophys.J. 482 (1997) 621
Subject astro-ph
Abstract[Abridged abstract:] Recent numerical simulations show that many $lyal$ absorption lines of column densities $ ha la 10^{15}$ cm$^{-2}$ are produced in transient, mini pancakes. Such pancakes are modeled here, approximating the initial perturbation leading to the formation of the pancake as a single sinusoidal wave. The density and temperature profiles of the gas in the pancake are determined for $z_c sim 3$, where $z_c$ is the collapse redshift. The $lyal$ absorption line profiles for a line of sight through the pancake are then calculated. The absorption lines in general have wings signifying bulk motions in the gas. It is shown that the deviation from a single Voigt profile is large for small H I column density lines, in which the effect of bulk motions is large. For lines with $ ha > 10^{13}$ cm$^{-2}$, high temperature tend to wash out the signatures of bulk motion. The analytical modeling of mini pancakes associated with $lyal$ forest lines --- with $10^{13} la ha la 10^{15}$ cm$^{-2}$---gives the corresponding mass scales. It is shown here that, for typical values of cosmological parameters, absorption lines with $ ha sim 10^{14}$ cm$^{-2}$ correspond to structures with baryonic mass of $M_b sim 10^{10}$ M$_{odot}$ with an overdensity of $sim 10$ at $z sim 3$. The value of $ ha$ can change by a factor $sim 3$ in the course of evolution of the pancake in time. It is also shown that there is an upper limit to $ ha$ from a pancake due to the slow recombination rate and the importance of collisional ionization at high temperatures. Mini pancakes do not give rise to $lyal$ lines with $ ha ga 10^{14.5}$ cm$^{-2}$, for $j21=1$ and $Omega_{IGM} sim 0.03$.
Source arXiv, astro-ph/9701054
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