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Title:
Non-Gaussian Features of Transmitted Flux of QSOs' Lyα Absorption: Intermittent Exponent
Authors:
Pando, Jesus; Feng, Long-Long; Jamkhedkar, Priya; Zheng, Wei; Kirkman, David; Tytler, David; Fang, Li-Zhi
Affiliation:
AA(Department of Physics, DePaul University, Chicago, IL 60614.), AB(Center for Astrophysics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China.; National Astronomical Observatories, Chinese Academy of Science, Chao-Yang District, Beijing 100012, People's Republic of China.), AC(Department of Physics, University of Arizona, Tucson, AZ 85721.), AD(Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218-2686.), AE(Center of Astrophysics and Astronomy, University of California, San Diego, La Jolla, CA 92093.), AF(Center of Astrophysics and Astronomy, University of California, San Diego, La Jolla, CA 92093.), AG(Department of Physics, University of Arizona, Tucson, AZ 85721.)
Publication:
The Astrophysical Journal, Volume 574, Issue 2, pp. 575-589. (ApJ Homepage)
Publication Date:
08/2002
Origin:
UCP
ApJ Keywords:
Cosmology: Theory, Galaxies: Intergalactic Medium, Cosmology: Large-Scale Structure of Universe, Galaxies: Quasars: Absorption Lines
DOI:
10.1086/341062
Bibliographic Code:
2002ApJ...574..575P

Abstract

Recently, it has been found that the field traced by QSOs' Lyα forests is intermittent on small scales. Intermittent behavior is essential for understanding the statistics and dynamics of cosmic gravitational clustering in the nonlinear regime. The most effective method of describing intermittency uses the structure functions and the intermittent exponent, which measure the scale and order dependencies of the ratio between the higher order and second-order moments of the field. These properties can be used not only to confirm the non-Gaussianity of fields but also to detect the type of non-Gaussianity. In this paper, we calculate the structure function and intermittent exponent of (1) Keck data, which consists of 28 high-resolution, high signal-to-noise ratio QSO Lyα absorption spectra, and (2) Lyα forest simulation samples produced via the pseudohydrodynamic scheme for the low-density cold dark matter model and warm dark matter (WDM) model with particle mass mW=300, 600, 800, and 1000 eV. Aside from the WDM model with mW=300 eV, the simulation samples are in agreement with observations in the context of the power spectrum. We find, however, that the intermittent behavior of all the simulation samples is substantially inconsistent, both quantitatively and qualitatively, with the Keck data. Specifically, (1) the structure functions of the simulation samples are significantly larger than that of Keck data on scales k>=0.1 km-1 s; (2) the intermittent exponents of the simulation samples are more negative than that of Keck data on all redshifts considered; and (3) the order dependence of the structure functions of simulation samples is closer to the intermittency of hierarchical clustering on all scales, while the Keck data are closer to a lognormal field on small scales. These differences are independent of noise and show that the intermittent evolution modeled by the pseudohydrodynamic simulation is substantially different from observations, even though they are in good agreement with each other in terms of second- and lower order statistics. This result also shows that ``weakly'' clustered samples, such as the high-resolution Lyα absorption spectrum, are effective in testing dynamical models of structure formation if their intermittent features are considered.
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