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Register a new userNon-Gaussian Features of Transmitted Flux of QSOs Ly$alpha$ Absorption: Intermittent Exponent
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Authors
Jesus Pando
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We calculate the structure function and intermittent exponent of the 1.) Keck data, which consists of 29 high resolution, high signal to noise ratio (S/N) QSO Ly$alpha$ absorption spectra, and 2.)the Ly$alpha$ 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. These two measures detect not only non-gaussianities, but also the type of non-gaussianty in the the field. We find that, 1.) the structure functions of the simulation samples are significantly larger than that of Keck data on scales less than about 100 h$^{-1}$ kpc, 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 in terms of second and lower order statistics. (Abridged)
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It has been recently found that the local fluctuations of the QSOs Ly$alpha$ absorption spectrum transmitted flux show spiky structures. This implies that the mass fields of the intergalactic medium (IGM) is intermittent. This feature cannot be explained by the clustering evolution of cosmic mass field in the linear regimes and is also difficult to incorporate into the hierarchical clustering scenario. We calculate the structure functions and intermittent exponent of the IGM and HI for full hydrodynamical simulation samples. The result shows the intermittent features of the Ly$alpha$ transmitted flux fluctuations as well as the mass field of the IGM. We find that within the error bars of current data, all the intermittent behavior of the simulation samples are consistent with the observation. This result is different from our earlier result (Pando et al 2002), which shows that the intermittent behavior of samples generated by pseudo-hydro simulation cannot be fitted with observed data. One difference between the pseudo-hydro and full hydro simulations is in treating the dynamical relation between the IGM (or HI) and dark matter fields. The former assumes that the IGM density distribution traces the underlying dark matter point-by-point on scales larger than the Jeans length in either the linear or nonlinear regimes. However, hydrodynamic studies have found that a statistical discrepancy between the IGM field and underlying dark matter in nonlinear regime is possible. We find that the point-by-point correlation between the IGM density perturbations and dark matter become weaker on comoving scales less than 2 h$^{-1}$ Mpc (in LCDM model), which is larger than the IGM Jeans length.
We present an analysis of the non-Gaussianity in the distribution of Ly$alpha$ forest lines in the QSO absorption spectra. Statistical tests performed on this data indicate that there may be large scale structure even though the power spectrum of the Ly$alpha$ line distribution on large scales is found to be flat. It is apparent that higher (than two) order statistics are crucial in quantifying the clustering behavior of Ly$alpha$ clouds. Using the discrete wavelet on three independent data sets of Ly$alpha$ forests, we find that the distribution of Ly$alpha$ forests does show non-Gaussian behavior on scales from 5 to 10 h$^{-1}$ Mpc with confidence level larger than 95%. Two data sets available on large scales are found to be non-Gaussian on even larger scales. These techniques are effective in discriminating among models of the Ly$alpha$ forest formation, which are degenerate at second and lower order statistics (abridged).
We have studied the power spectrum and the intermittent behavior of the fluctuations in the transmitted flux of HE2347-4342 ${rm Ly}{alpha}$ absorption in order to investigate if there is any discrepancy between the LCDM model with parameters given by the WMAP and observations on small scales. If the non-Gaussianity of cosmic mass field is assumed to come only from halos with an universal mass profile of the LCDM model, the non-Gaussian behavior of mass field would be effectively measured by its intermittency, because intermittency is a basic statistical feature of the cuspy structures. We have shown that the Ly$alpha$ transmitted flux field of HE2347-4342 is significantly intermittent on small scales. With the hydrodynamic simulation, we demonstrate that the LCDM model is successful in explaining the power spectrum and intermittency of ${rm Ly}{alpha}$ transmitted flux. Using statistics ranging from the second to eighth order, we find no discrepancy between the LCDM model and the observed transmitted flux field, and no evidence to support the necessity of reducing the power of density perturbations relative to the standard LCDM model up to comoving scales as small as about $0.08 {rm h}^{-1} {rm Mpc}$. Moreover, our simulation samples show that the intermittent exponent of the Ly$alpha$ transmitted flux field is probably scale-dependent. This result is different from the prediction of universal mass profile with a constant index of the central cusp. The scale-dependence of the intermittent exponent indicates that the distribution of baryonic gas is decoupled from the underlying dark matter.
The forest of Lyman-alpha absorption lines seen in the spectra of distant quasars has become an important probe of the distribution of matter in the Universe. We use large, hydrodynamical simulations from the OWLS project to investigate the effect of feedback from galaxy formation on the probability distribution function and the power spectrum of the Lyman-alpha transmitted flux. While metal-line cooling is unimportant, both galactic outflows from massive galaxies driven by active galactic nuclei and winds from low-mass galaxies driven by supernovae have a substantial impact on the flux statistics. At redshift z=2.25, the effects on the flux statistics are of a similar magnitude as the statistical uncertainties of published data sets. The changes in the flux statistics are not due to differences in the temperature-density relation of the photo-ionised gas. Instead, they are caused by changes in the density distribution and in the fraction of hot, collisionally ionised gas. It may be possible to disentangle astrophysical and cosmological effects by taking advantage of the fact that they induce different redshift dependencies. In particular, the magnitude of the feedback effects appears to decrease rapidly with increasing redshift. Analyses of Lyman-alpha forest data from surveys that are currently in process, such as BOSS/SDSS-III and X-Shooter/VLT, must take galactic winds into account.
We have compiled all available data on chemical abundances in damped Lyman alpha absorption systems for comparison with results from our combined chemical and spectrophotometric galaxy evolution models. Preliminary results from chemically consistent calculations are in agreement with observations of damped Ly$alpha$ systems.
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