Non‐Gaussian Features of Transmitted Flux of QSOs' Lyα Absorption: Intermittent Exponent

Abstract

Recently, it has been found that the field traced by QSO's 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 to 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 (S/N) QSO Lyα absorption spectra, and 2.) Lyα forest simulation samples produced via the pseudo hydro scheme for the low density cold dark matter (LCDM) model and warm dark matter (WDM) model with particle mass m W = 300, 600, 800 and 1000 eV. Aside from the WDM model with m W = 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 exponent of the simulation samples is more negative than that of Keck data on all redshifts considered, 3.) the order-dependence of the structure functions of simulation samples are 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 pseudo-hydro 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, like high resolution Lyα absorption spectrum, are effective in testing dynamical models of structure formation if their intermittent features are considered.Subject headings: cosmology: theory -large-scale structure of the universe

The Velocity Field of Baryonic Gas in the Universe

“…For example, the transmitted flux of a QSO's Ly absorption is found to be significantly intermittent, and its probability distribution functions ( pdf ) are long tailed and probably lognormal (Jamkhedkar et al 2000(Jamkhedkar et al , 2003Pando et al 2002;Feng et al 2003). This is consistent with the intermittent spatial and temporal behavior of a developed Burgers fluid ( Polyakov 1995;Bouchaud et al 1995;Gurarie & Migdal 1996;Balkovsky et al 1997;Yakhot 1998;Frisch et al 2001).…”

Astrophysics in 2002

“…As the default option, we will vote for the clouds not only being distributed like other stuff, but for that distribution being nicely fit by L-CDM considerations (Phillips et al 2001a). But if you don't like that, you can vote for intermittency (Pando et al 2002). Meaning?…”

Statistical Features of 21 Centimeter Emission from the Epoch between Reionization and the Gunn‐Peterson Transparency

“…This property has already been found to be useful in explaining the intermittence of the transmitted flux of QSOs' Ly absorption spectrum (Jamkhedkar et al 2000(Jamkhedkar et al , 2003Pando et al 2002). The long tail can directly be seen with (1) the cumulative mass fraction M (>=), which is the fraction of mass in regions having mass density larger than a given , and (2) the volume filling factor V (>=), which is the fraction of volume with density larger than a given .…”