Lyman alpha absorption lines from mini pancakes

Abstract

[Abridged abstract:] Recent numerical simulations show that many $\lyal$ absorption lines of column densities $\nha \la 10^{15}$ 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 $\nha > 10^{13}$ 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 $10^{13} \la \nha \la 10^{15}$ cm${}^{-2}$---gives the corresponding mass scales. It is shown here that, for typical values of cosmological parameters, absorption lines with $\nha \sim 10^{14}$ 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 $\nha$ 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 $\nha$ 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 $\nha \ga 10^{14.5}$ cm${}^{-2}$, for $\j21=1$ and ${\Omega }_{IGM}\sim 0.03$.

Latex with aaspp4.sty (25 pages), 6 figures, Accepted for publication in The Astrophysical Journal

References in corpus (4)

• The Lyman Alpha Forest from Gravitational Collapse in the CDM+Lambda Model
• A Multi-Species Model for Hydrogen and Helium Absorbers in Lyman-Alpha Forest Clouds
• THE GUNN-PETERSON EFFECT FROM UNDERDENSE REGIONS IN A PHOTOIONIZED INTERGALACTIC MEDIUM
• Warm Gas at High Redshift - Clues to Gravitational Structure Formation from Optical Spectroscopy of Lyman Alpha Absorption Systems

Cited by in corpus (4)

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• Sheets and Filaments as the Origin of the High-Velocity Tail of the Lyman-Alpha Forest
• Properties of observed Ly-$\alpha$ forest