A Simulation of LY alpha Absorption Forests in Linear Approximation of Cold Dark Matter and Cold Plus Hot Dark Matter Models

Bi, Hongguang; Ge, J.; Fang, Li‐Zhi

doi:10.1086/176282

Cited by 47 publications

(65 citation statements)

References 30 publications

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“…The pressure gradients are generally smaller than gravitational forces. The distribution of cool baryonic di †use matter is almost point-by-point proportional to the underlying dark matter density (Bi, Ge, & Fang 1995).…”

Section: T He L Ocal Dw T Power Spectrummentioning

confidence: 99%

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

Zhan

Jamkhedkar

Fang

2001

ApJ

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We analyze the power spectrum of a QSOÏs Lya-transmitted Ñux 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 di †er-ent 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 Lya-transmitted Ñux of the QSO HS 1700, we Ðnd that the underlying cosmic mass Ðeld of the transmitted Ñux 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 EinsteinÈde Sitter universe. However, the nonlinear features of the clustering show di †erences on di †erent scale ranges : (1) On physical scales larger than D1.3 h~1 Mpc, the Ðeld is almost Gaussian.(2) On scales 1.3È0.3 h~1 Mpc, the Ðeld is consistent with the correlation hierarchy with a constant value for the coefficient (3) On scales less than 300 h~1 kpc, the Ðeld is no longer Gaussian but essentially Q 4 . intermittent. In this case, the Ðeld can still be Ðtted by the correlation hierarchy, but the coefficient, Q 4 , should be scale dependent. These three points are strongly supported by the following result : the scale dependencies of given by two statistically independent measures, i.e., by roughness and by Q 4 Q 4 R Q 4 C scale-scale correlation, are the same in the entire scale range considered.

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Section: T He L Ocal Dw T Power Spectrummentioning

confidence: 99%

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

Zhan

Jamkhedkar

Fang

2001

ApJ

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“…Initially Gaussian density perturbations will give rise to a lognormal density field when the initial peculiar velocity field is also Gaussian (Coles & Jones 1991). Indeed, Bi et al (1992) demonstrated that a lognormal density distribution can produce many properties of the observed Ly forest (see also Bi et al 1995;Bi & Davidsen 1997). More generally, however, a lognormal optical depth distribution may naturally arise from a nonlognormal density distribution as a result of the central limit theorem, since temperature and ionization rate are multiplicative contributing factors that are likely to be multivalued.…”

Section: Introductionmentioning

confidence: 99%

The Evolution of Optical Depth in the Lyα Forest: Evidence Against Reionization atz∼6

Becker

Rauch

Sargent

2007

ApJ

243

299

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We examine the evolution of the IGM Ly optical depth distribution using the transmitted flux probability distribution function (PDF) in a high-resolution sample of 55 QSOs spanning absorption redshifts 1:7 < z < 5:8. The data are compared to two theoretical distributions: a model distribution based on the density distribution of MiraldaEscudé et al. (2000;MHR00) and a lognormal distribution. Assuming a spatially uniform UV background and an isothermal IGM, as was done in previous works where transmitted flux statistics have been used to infer an end to cosmic reionization at z $ 6, the MHR00 model fails to reproduce the observed flux PDFs at redshifts where the optical depth distribution is well sampled unless large continuum corrections are applied. A lognormal distribution, in contrast, fits the data well at all redshifts with only minor continuum adjustments. Extrapolating the evolution of the lognormal distribution at z < 5:4 predicts the observed upturn in the Ly and Ly effective optical depths at z > 5:7, while simultaneously reproducing the mean transmitted flux down to z ¼ 1:6. In this empirical sense, the evolution of the Ly forest at z $ 6 is consistent with observed trends at lower redshift. If the evolution of the forest at z P 5 reflects a slowly evolving density field, temperature, and UV background, then no sudden change in the IGM, such as one due to late reionization, appears necessary to explain the disappearance of transmitted flux at z $ 6. If the MHR00 density distribution is correct, then a nonuniform UV background and/or IGM temperature may be required to produce the correct distribution of optical depths. We find that an inverse temperature-density relation for the MHR00 model significantly improves the PDF fits, but with a large scatter in the equation-of-state index. Subject headingg s: cosmology: observations -early universe -intergalactic mediumquasars: absorption lines

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“…These clouds have been shown to originate in the mildly nonlinear density regions of the IGM (Cen & Ostriker 1994). This has allowed development of detailed semi-analytic methods to understand the observed properties of these clouds (e.g., Bi et al 1995;Choudhury et al 2001aChoudhury et al , 2001b. Adopting a semianalytic approach, we simulate density fluctuation along the line of sight, including the contribution of matter perturbations induced by these magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

PROBING PRIMORDIAL MAGNETIC FIELDS USING Lyα CLOUDS

Pandey¹,

Sethi²

2012

ApJ

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From previous studies of the effect of primordial magnetic fields on early structure formation, we know that the presence of primordial magnetic fields during early structure formation could induce more perturbations at small scales (at present 1-10 h −1 Mpc) as compared to the usual ΛCDM theory. Matter power spectra over these scales are effectively probed by cosmological observables such as shear correlation and Lyα clouds. In this paper we discuss the implications of primordial magnetic fields on the distribution of Lyα clouds. We simulate the line-ofsight density fluctuation including the contribution coming from the primordial magnetic fields. We compute the evolution of Lyα opacity for this case and compare our theoretical estimates of Lyα opacity with the existing data to constrain the parameters of the primordial magnetic fields. We also discuss the case when the two density fields are correlated. Our analysis yields an upper bound of roughly 0.3-0.6 nG on the magnetic field strength for a range of nearly scale-invariant models, corresponding to a magnetic field power spectrum index n −3.

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A Simulation of LY alpha Absorption Forests in Linear Approximation of Cold Dark Matter and Cold Plus Hot Dark Matter Models

Cited by 47 publications

References 30 publications

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

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

The Evolution of Optical Depth in the Lyα Forest: Evidence Against Reionization atz∼6

PROBING PRIMORDIAL MAGNETIC FIELDS USING Lyα CLOUDS

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