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Register a new userConstraints on Cosmological Parameters from the Lyman-alpha Forest Power Spectrum and COBE-DMR
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We combine COBE-DMR measurements of cosmic microwave background anisotropy with a recent measurement of the mass power spectrum at redshift z=2.5 from Lya forest data to derive constraints on cosmological parameters and test the inflation+CDM scenario of structure formation. By treating the inflationary spectral index n as a free parameter, we can find successful fits to the COBE and Lya forest constraints in Omega_m=1 models with and without massive neutrinos and in low-Omega_m models with and without a cosmological constant. Within each class of model, the combination of COBE and the Lya forest P(k) constrains a parameter combination of the form (Omega_m h^a n^b Omega_b^c), with different indices for each case. This new constraint breaks some of the degeneracies in cosmological parameter determinations from other measurements. The Lya forest P(k) provides the first measurement of the slope of the linear mass power spectrum on ~Mpc scales, and it confirms a basic prediction of the inflationary CDM scenario: a nearly scale-invariant spectrum of primeval fluctuations (n~1) that bends towards k^{n-4} on small scales. Considering additional observational data, we find that COBE-normalized, Omega_m=1 models that match the Lya forest P(k) do not match the observed masses of rich galaxy clusters and that a low-Omega_m model with a cosmological constant provides the best overall fit, even without the direct evidence for cosmic acceleration from supernovae. Modest improvements in the Lya forest P(k) measurement could greatly restrict the allowable region of parameter space for CDM models, constrain the contribution of tensor fluctuations to CMB anisotropy, and achieve a more stringent test of the current consensus model of structure formation.
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We present constraints on masses of active and sterile neutrinos. We use the one-dimensional Ly$alpha$-forest power spectrum from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) and from the VLT/XSHOOTER legacy survey (XQ-100). In this paper, we present our own measurement of the power spectrum with the publicly released XQ-100 quasar spectra. Fitting Ly$alpha$ data alone leads to cosmological parameters in excellent agreement with the values derived independently from Planck 2015 Cosmic Microwave Background (CMB) data. Combining BOSS and XQ-100 Ly$alpha$ power spectra, we constrain the sum of neutrino masses to $sum m_ u < 0.8$ eV (95% C.L). With the addition of CMB data, this bound is tightened to $sum m_ u < 0.14$ eV (95% C.L.). With their sensitivity to small scales, Ly$alpha$ data are ideal to constrain $Lambda$WDM models. Using XQ-100 alone, we issue lower bounds on pure dark matter particles: $m_X gtrsim 2.08 : rm{keV}$ (95% C.L.) for early decoupled thermal relics, and $m_s gtrsim 10.2 : rm{keV}$ (95% C.L.) for non-resonantly produced right-handed neutrinos. Combining the 1D Ly$alpha$ forest power spectrum measured by BOSS and XQ-100, we improve the two bounds to $m_X gtrsim 4.17 : rm{keV}$ and $m_s gtrsim 25.0 : rm{keV}$ (95% C.L.). The $3~sigma$ bound shows a more significant improvement, increasing from $m_X gtrsim 2.74 : rm{keV}$ for BOSS alone to $m_X gtrsim 3.10 : rm{keV}$ for the combined BOSS+XQ-100 data set. Finally, we include in our analysis the first two redshift bins ($z=4.2$ and $z=4.6$) of the power spectrum measured with the high-resolution HIRES/MIKE spectrographs. The addition of HIRES/MIKE power spectrum allows us to further improve the two limits to $m_X gtrsim 4.65 : rm{keV}$ and $m_s gtrsim 28.8 : rm{keV}$ (95% C.L.).
We present the Lyman-$alpha$ flux power spectrum measurements of the XQ-100 sample of quasar spectra obtained in the context of the European Southern Observatory Large Programme Quasars and their absorption lines: a legacy survey of the high redshift universe with VLT/XSHOOTER. Using $100$ quasar spectra with medium resolution and signal-to-noise ratio we measure the power spectrum over a range of redshifts $z = 3 - 4.2$ and over a range of scales $k = 0.003 - 0.06,mathrm{s,km^{-1}}$. The results agree well with the measurements of the one-dimensional power spectrum found in the literature. The data analysis used in this paper is based on the Fourier transform and has been tested on synthetic data. Systematic and statistical uncertainties of our measurements are estimated, with a total error (statistical and systematic) comparable to the one of the BOSS data in the overlapping range of scales, and smaller by more than $50%$ for higher redshift bins ($z>3.6$) and small scales ($k > 0.01,mathrm{s,km^{-1}}$). The XQ-100 data set has the unique feature of having signal-to-noise ratios and resolution intermediate between the two data sets that are typically used to perform cosmological studies, i.e. BOSS and high-resolution spectra (e.g. UVES/VLT or HIRES). More importantly, the measured flux power spectra span the high redshift regime which is usually more constraining for structure formation models.
We use the probability distribution function (PDF) of the lya forest flux at z=2-3, measured from high-resolution UVES/VLT data, and hydrodynamical simulations to obtain constraints on cosmological parameters and the thermal state of the intergalactic medium (IGM) at z 2-3. The observed flux PDF at z=3 alone results in constraints on cosmological parameters in good agreement with those obtained from the WMAP data, albeit with about a factor two larger errors. The observed flux PDF is best fit with simulations with a matter fluctuation amplitude of sigma_8=0.8-0.85 pm 0.07 and an inverted IGM temperature-density relation (gamma ~ 0.5-0.75), consistent with our previous results obtained using a simpler analysis. These results appear to be robust to uncertainties in the quasar (QSO) continuum placement. We further discuss constraints obtained by a combined analysis of the high-resolution flux PDF and the power spectrum measured from the Sloan Digital Sky Survey (SDSS) lya forest data. The joint analysis confirms the suggestion of an inverted temperature-density relation, but prefers somewhat higher values (sigma_8 ~ 0.9) of the matter fluctuation amplitude than the WMAP data and the best fit to the flux PDF alone. The joint analysis of the flux PDF and power spectrum (as well as an analysis of the power spectrum data alone) prefers rather large values for the temperature of the IGM, perhaps suggesting that we have identified a not yet accounted for systematic error in the SDSS flux power spectrum data or that the standard model describing the thermal state of the IGM at z ~ 2-3 is incomplete.
We present constraints on neutrino masses, the primordial fluctuation spectrum from inflation, and other parameters of the $Lambda$CDM model, using the one-dimensional Ly$alpha$-forest power spectrum measured by Palanque-Delabrouille et al. (2013) from SDSS-III/BOSS, complemented by Planck 2015 cosmic microwave background (CMB) data and other cosmological probes. This paper improves on the previous analysis by Palanque-Delabrouille et al. (2015) by using a more powerful set of calibrating hydrodynamical simulations that reduces uncertainties associated with resolution and box size, by adopting a more flexible set of nuisance parameters for describing the evolution of the intergalactic medium, by including additional freedom to account for systematic uncertainties, and by using Planck 2015 constraints in place of Planck 2013. Fitting Ly$alpha$ data alone leads to cosmological parameters in excellent agreement with the values derived independently from CMB data, except for a weak tension on the scalar index $n_s$. Combining BOSS Ly$alpha$ with Planck CMB constrains the sum of neutrino masses to $sum m_ u < 0.12$ eV (95% C.L.) including all identified systematic uncertainties, tighter than our previous limit (0.15 eV) and more robust. Adding Ly$alpha$ data to CMB data reduces the uncertainties on the optical depth to reionization $tau$, through the correlation of $tau$ with $sigma_8$. Similarly, correlations between cosmological parameters help in constraining the tensor-to-scalar ratio of primordial fluctuations $r$. The tension on $n_s$ can be accommodated by allowing for a running ${mathrm d}n_s/{mathrm d}ln k$. Allowing running as a free parameter in the fits does not change the limit on $sum m_ u$. We discuss possible interpretations of these results in the context of slow-roll inflation.
Absorption between the rest-frame wavelengths of 973 and 1026 Angstroms in quasar spectra arises from two sources (apart from occasional metals): one is due to Lyman-alpha (Lya) absorption by materials at a low redshift, and the other from Lyman-beta (Lyb) at a higher redshift. These two sources of absorption are to a good approximation uncorrelated because of their wide physical separation. Therefore, the two-point correlation of absorption in this region of quasar spectra neatly factorizes into two pieces: the Lyb correlation at high z, and the Lya correlation at low z. The latter can be independently measured from quasar spectra at lower redshifts using current techniques. A simple division then offers a way to statistically separate out the Lyb two-point correlation from the Lya correlation. Several applications of this technique are discussed. First, since the Lyb absorption cross-section is lower than Lya by about a factor of 5, the Lyb forest is a better probe of the intergalactic medium (IGM) at higher redshifts where Lya absorption is often saturated. Second, for the same reason, the Lyb forest allows a better measurement of the equation of state of the IGM at higher overdensities, yielding stronger constraints on its slope when used in conjunction with the Lya forest. Third, models of the Lya forest based on gravitational instability make unique predictions for the Lyb forest, which can be tested against observations. We briefly point out that feedback processes that affect higher density regions but leave low density structure intact may be better constrained by the Lyb forest.
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