Priya Jamkhedkar

A unified fitting of HI and HeII Ly alpha transmitted flux of QSO HE 2347-4342 with Lambda CDM hydrodynamic simulations

Using cosmological hydrodynamic simulations of the ΛCDM model, we present a comparison between the simulation sample and real data sample of H I and He II Lyα transmitted flux in the absorption spectra of the QSO HE 2347-4342. The ΛCDM model is successful in simultaneously explaining the statistical features of both H I and He II Lyα transmitted flux. It includes the following features: (1) The power spectra of the transmitted flux of H I and He II can be well fitted on all scales ≥0.28 h-1 Mpc for H and ≥1.1 h-1 Mpc for He. (2) The Doppler parameters of absorption features of He II and H I are found to be turbulent broadening. (3) The ratio of He II to H I optical depths are substantially scattered, due to the significant effect of noise. A large part of the η scatter is due to the noise in the He II flux. However, the real data contain more low-η events than the simulation sample. This discrepancy may indicate that the mechanism leading extra fluctuations on the simulation data, such as a fluctuating UV radiation background, is needed. Yet models of these extra fluctuations should satisfy the following constraints: (1) If the fluctuations are Gaussian, they should be limited by the power spectra of observed H I and He II flux. (2) If the fluctuations are non-Gaussian, they should be limited by the observed non-Gaussian features of the H I and He II flux.

The Local Power Spectrum and Correlation Hierarchy of the Cosmic Mass Field

We analyze the power spectrum of a QSOs Lyα-transmitted flux in the discrete wavelet transform (DWT) representation. Although the mean DWT power spectrum is consistent with its counterpart in Fourier representation, the spatial distribution of the local power varies greatly; i.e., the local DWT power spectra show remarkably spiky structures on small scales. To measure these spiky features, we introduce the quantities roughness of the local power spectrum and correlation between spikes on different scales. We then test the predictions made by the correlation hierarchy model on the roughness and the scale-scale correlations of the local power spectrum. Using the Lyα-transmitted flux of the QSO HS 1700, we find that the underlying cosmic mass field of the transmitted flux at redshift around z 2.2 can be described by the hierarchical clustering model on physical scales from 2.5 h-1 Mpc to a few tens h-1 kpc in an Einstein-de Sitter universe. However, the nonlinear features of the clustering show differences on different scale ranges: (1) On physical scales larger than ~1.3 h-1 Mpc, the field is almost Gaussian. (2) On scales 1.3-0.3 h-1 Mpc, the field is consistent with the correlation hierarchy with a constant value for the coefficient Q4. (3) On scales less than 300 h-1 kpc, the field is no longer Gaussian but essentially intermittent. In this case, the field can still be fitted by the correlation hierarchy, but the coefficient, Q4, should be scale dependent. These three points are strongly supported by the following result: the scale dependencies of Q4 given by two statistically independent measures, i.e., Q by roughness and Q by scale-scale correlation, are the same in the entire scale range considered.

On the Normalization of the QSO Lyα Forest Power Spectrum

The calculation of the transmission power spectrum of QSO Lyα absorption requires two parameters for the normalization: the continuum Fc and mean transmission -τ. Traditionally, the continuum is obtained by a polynomial fitting truncating it at a lower order, and the mean transmission is calculated over the entire wavelength range considered. The flux F is then normalized by Fc-τ. However, the fluctuations in the transmitted flux are significantly correlated with the local background flux on scales for which the field is intermittent. As a consequence, the normalization of the entire power spectrum by an overall mean transmission -τ will overlook the effect of the fluctuation-background correlation upon the powers. In this paper we develop a self-normalization algorithm of the transmission power spectrum based on a multiresolution analysis. This self-normalized power spectrum estimator needs neither a continuum fitting nor a predetermining of the mean transmission. With simulated samples, we show that the self-normalization algorithm can perfectly recover the transmission power spectrum from the flux regardless of how the continuum varies with wavelength. We also show that the self-normalized power spectrum is also properly normalized by the mean transmission. Moreover, this power spectrum estimator is sensitive to the nonlinear behavior of the field. That is, the self-normalized power spectrum estimator can distinguish between fields with or without the fluctuation-background correlation. This cannot be accomplished by the power spectrum with the normalization by an overall mean transmission. Applying this analysis to a real data set of Q1700+642 Lyα forest, we demonstrate that the proposed power spectrum estimator can perform correct normalization and effectively reveal the correlation between the fluctuations and background of the transmitted flux on small scales. Therefore, the self-normalized power spectrum would be useful for the discrimination among models without the uncertainties caused by free (or fitting) parameters.

Power Spectrum and Intermittency of Lyα Transmitted Flux of QSO HE 2347–4342

We have studied the power spectrum and the intermittent behavior of the fluctuations in the transmitted flux of HE 2347-4342 Lyα absorption in order to investigate if there is any discrepancy between the ΛCDM model with parameters given by the WMAP and observations on small scales. If the non-Gaussianity of the cosmic mass field is assumed to come only from halos with a universal mass profile of the ΛCDM 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 Lyα transmitted flux field of HE 2347-4342 is significantly intermittent on small scales. With the hydrodynamic simulation, we demonstrate that the ΛCDM model is successful in explaining the power spectrum and intermittency of Lyα transmitted flux. Using statistics ranging from second to eighth order, we find no discrepancy between the ΛCDM 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 ΛCDM model up to comoving scales as small as about 0.08 h-1 Mpc. Moreover, our simulation samples show that the intermittency exponent of the Lyα transmitted flux field is probably scale-dependent. This result is different from the prediction of a universal mass profile with a constant power index of the central cusp. The scale dependence of the intermittency exponent indicates that the distribution of baryonic gas is decoupled from the underlying dark matter.

The Intermittent Behavior of the Cosmic Mass Field Revealed by a QSO's Lyα Forest

The intermittent behavior of the space-scale distribution of Ly

The Intermittent Behavior of the Cosmic Mass Field Revealed by a L[CLC]y[/CLC]α Forest QSO

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The Intermittent Behavior of the Cosmic Mass Field Revealed by a QSO's Ly? Forest

transmitted flux of QSO HS1700+64 has been analyzed via a discrete wavelet transform. We found that there are strong indications of intermittency on scales down to about 10

Intermittency and Large‐Scale Structure in the Universe: A New Window for the Study of the Nonlinear Regime of Structure Formation

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Intermittent behavior of cosmic mass field revealed by QSO's Ly_alpha forests

kpc. These are: 1.) the probability distribution function of the local fluctuations of the flux is significantly long-tailed on small scales, and 2.) the local power spectrum of the flux shows prominent spiky structures on small scales. Moreover, the local power spectrum averaged on regions with different sizes shows similar spiky structures. Therefore, the random mass density field traced by the Ly

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

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