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Register a new userDetecting the non-Gaussian Spectrum of QSOs Ly$alpha$ Absorption Line Distribution
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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).
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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)
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.
Using a discrete wavelet based space-scale decomposition (SSD), the spectrum of the skewness and kurtosis is developed to describe the non-Gaussian signatures in cosmologically interesting samples. Because the basis of the discrete wavelet is compactly supported, the one-point distribution of the father function coefficients (FFCs) taken from one realization is a good estimate of the probability distribution function of the density if the ``fair sample hypothesis holds. These FFC one-point distributions can also avoid the constraints of the central limit theorem on the detection of non-Gaussianity. Thus the FFC one-point distributions are effective in detecting non-Gaussian behavior in samples such as non-Gaussian clumps embedded in a Gaussain background, regardless of the number or density of the clumps. We demonstrate that the non-Gaussianity can reveal not only the magnitudes but also the scales of non-Gaussianity. Also calculated are the FFC one-point distributions, skewness and kurtosis spectra for real data and linearly simulated samples of QSO Ly$alpha$ forests. When considering only second and lower order of statistics, such as the number density and two-point correlation functions, the simulated data show the same features as the real data. However, the the kurtosis spectra of samples given by different models are found to be different. On the other hand, the spectra of skewness and kurtosis for independent observational data sets are found to be the same. Moreover, the real data are significantly different from the non-Gaussianity spectrum of various posssible random samples. Therefore the non-Gaussain spectrum is necessary and valuable for model discrimination.
Broad Absorption Line Quasars (BAL QSOs) have been found to be associated with extremely compact radio sources. These reduced dimensions can be either due to projection effects or these objects might actually be intrinsically small. Exploring these two hypotheses is important to understand the nature and origin of the BAL phenomenon because orientation effects are an important discriminant between the different models proposed to explain this phenomenon. In this work we present VLBA observations of 5 BAL QSOs and discuss their pc-scale morphology.
We have developed two independent methods to measure the one-dimensional power spectrum of the transmitted flux in the Lyman-$alpha$ forest. The first method is based on a Fourier transform, and the second on a maximum likelihood estimator. The two methods are independent and have different systematic uncertainties. The determination of the noise level in the data spectra was subject to a novel treatment, because of its significant impact on the derived power spectrum. We applied the two methods to 13,821 quasar spectra from SDSS-III/BOSS DR9 selected from a larger sample of over 60,000 spectra on the basis of their high quality, large signal-to-noise ratio, and good spectral resolution. The power spectra measured using either approach are in good agreement over all twelve redshift bins from $<z> = 2.2$ to $<z> = 4.4$, and scales from 0.001 $rm(km/s)^{-1}$ to $0.02 rm(km/s)^{-1}$. We determine the methodological and instrumental systematic uncertainties of our measurements. We provide a preliminary cosmological interpretation of our measurements using available hydrodynamical simulations. The improvement in precision over previously published results from SDSS is a factor 2--3 for constraints on relevant cosmological parameters. For a $Lambda$CDM model and using a constraint on $H_0$ that encompasses measurements based on the local distance ladder and on CMB anisotropies, we infer $sigma_8 =0.83pm0.03$ and $n_s= 0.97pm0.02$ based on ion{H}{i} absorption in the range $2.1<z<3.7$.
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