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Register a new userPower Spectrum and Intermittency of Ly${alpha}$ Transmitted Flux of QSO He2347-4342
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Priya Jamkhedkar
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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.
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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 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 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 $2.1<z<3.7$.
We present a new compilation of inferences of the linear 3D matter power spectrum at redshift $z,{=},0$ from a variety of probes spanning several orders of magnitude in physical scale and in cosmic history. We develop a new lower-noise method for performing this inference from the latest Ly$alpha$ forest 1D power spectrum data. We also include cosmic microwave background (CMB) temperature and polarization power spectra and lensing reconstruction data, the cosmic shear two-point correlation function, and the clustering of luminous red galaxies. We provide a Dockerized Jupyter notebook housing the fairly complex dependencies for producing the plot of these data, with the hope that groups in the future can help add to it. Overall, we find qualitative agreement between the independent measurements considered here and the standard $Lambda$CDM cosmological model fit to the {it Planck} data
We present a measurement of the 1D Ly$alpha$ forest flux power spectrum, using the complete Baryon Oscillation Spectroscopic Survey (BOSS) and first extended-BOSS (eBOSS) quasars at $z_{rm qso}>2.1$, corresponding to the fourteenth data release (DR14) of the Sloan Digital Sky Survey (SDSS). Our results cover thirteen bins in redshift from $z_{rm Lyalpha}=2.2$ to 4.6, and scales up to $k=0.02rm ,(km/s)^{-1}$. From a parent sample of 180,413 visually inspected spectra, we selected the 43,751 quasars with the best quality; this data set improves the previous result from the ninth data release (DR9), both in statistical precision (achieving a reduction by a factor of two) and in redshift coverage. We also present a thorough investigation of identified sources of systematic uncertainties that affect the measurement. The resulting 1D power spectrum of this work is in excellent agreement with the one from the BOSS DR9 data.
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