On the Normalization of the QSO Lyα Forest Power Spectrum

Jamkhedkar, Priya; Bi, Hongguang; Fang, Li‐Zhi

doi:10.1086/323216

Cited by 12 publications

(16 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…P u j is the power spectrum of the transmitted flux fluctuations ∆F = F − F . In Paper I, or Jamkhedkar, Bi & Fang (2001), and Yang et al (2001a), the power spectrum P u j differs from eq. (20) and (21) by a noise term.…”

Section: The Intermittent Exponent In the Dwt Basismentioning

confidence: 94%

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

Pando

Feng

Jamkhedkar

et al. 2002

ApJ

Self Cite

View full text Add to dashboard Cite

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

show abstract

Section: The Intermittent Exponent In the Dwt Basismentioning

confidence: 94%

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

Pando

Feng

Jamkhedkar

et al. 2002

ApJ

Self Cite

View full text Add to dashboard Cite

show abstract

“…Because the variable δτ r is given by the difference between τ( x + r ) and τ( x ), δτ r is independent of fluctuations of τ( x ) on scales larger than r . Therefore, the variable δτ r is actually insensitive to the continuum used in the data reduction (Jamkhedkar, Bi & Fang 2001).…”

Section: Log‐poisson Non‐gaussianity Of Observed Samplesmentioning

confidence: 99%

Log-Poisson non-Gaussianity of Lyα transmitted flux fluctuations at high redshift

Lu¹,

Zhu²,

Chu³

et al. 2010

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We investigate the non‐Gaussian features of the intergalactic medium (IGM) at redshift z∼ 5–6 using the Lyα transmitted flux of quasar absorption spectra and a cosmological hydrodynamic simulation of the concordance ΛCDM universe. We show that the neutral hydrogen mass density field and Lyα transmitted flux fluctuations possess all the non‐Gaussian features predicted by the log‐Poisson hierarchy. This depends only on two dimensionless parameters β and γ, describing, respectively, the intermittence and singularity of the random fields. We find that the non‐Gaussianity of the Lyα transmitted flux of quasars from z= 4.9 to z= 6.3 can be well reconstructed by the hydrodynamical simulation samples. Although the Gunn–Peterson optical depth and its variance undergoes a significant evolution in the redshift range of 5–6, the intermittency measured by β is almost redshift‐independent in this range. More interestingly, the intermittency of the quasar's absorption spectra on physical scales 0.1–1 h−1 Mpc in redshift 5–6 is found to be about the same as that on physical scales 1–10 h−1 Mpc at redshifts 2–4. Considering the Jeans length is less than 0.1 h−1 Mpc at z∼ 5, and 1 h−1 Mpc at z∼ 2, these results imply that the non‐linear evolution in high and low redshifts will lead the cosmic baryon fluid to a state similar to fully developed turbulence. The log‐Poisson high‐order behaviour of the current high‐redshift data of a quasar's spectrum can be explained by the uniform ultraviolet background in the redshift range considered. We have also studied the log‐Poisson non‐Gaussianity by considering an inhomogeneous background. With several simplified models of the inhomogeneous background, we have found that the effect of the inhomogeneous background on the log‐Poisson non‐Gaussianity is no larger than 1σ.

show abstract

“…Moreover, the real data of He are highly noisy; for some pixels, the S/ N is lower than 1, and some pixels have negative flux. To eliminate the effect of these pixels on the power spectrum calculation, we should use the algorithm of denoising or conditional counting as in Paper I ( Donoho 1995;Jamkhedkar et al 2001).…”

Section: Power Spectrummentioning

confidence: 99%

A Unified Fitting of Hiand HeiiLyα Transmitted Flux of QSO HE 2347−4342 with ΛCDM Hydrodynamic Simulations

Liu

Jamkhedkar

Zheng

et al. 2006

ApJ

Self Cite

View full text Add to dashboard Cite

Using cosmological hydrodynamic simulations of the ÃCDM model, we present a comparison between the simulation sample and real data sample of H i and He ii Ly transmitted flux in the absorption spectra of the QSO HE 2347À4342. The ÃCDM model is successful in simultaneously explaining the statistical features of both H i and He ii Ly 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 À1 Mpc for H and !1.1 h À1 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 scatter is due to the noise in the He ii flux. However, the real data contain more low-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 nonGaussian, they should be limited by the observed non-Gaussian features of the H i and He ii flux. Subject headingg s: cosmology: theory -large-scale structure of universe

show abstract

On the Normalization of the QSO Lyα Forest Power Spectrum

Cited by 12 publications

References 30 publications

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

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

Log-Poisson non-Gaussianity of Lyα transmitted flux fluctuations at high redshift

A Unified Fitting of Hiand HeiiLyα Transmitted Flux of QSO HE 2347−4342 with ΛCDM Hydrodynamic Simulations

Contact Info

Product

Resources

About