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Register a new userCosmological and astrophysical constraints from the Lyman-alpha forest flux probability distribution function
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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.
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The Ly$alpha$ forest transmission probability distribution function (PDF) is an established probe of the intergalactic medium (IGM) astrophysics, especially the temperature-density relationship of the IGM. We measure the transmission PDF from 3393 Baryon Oscillations Spectroscopic Survey (BOSS) quasars from SDSS Data Release 9, and compare with mock spectra that include careful modeling of the noise, continuum, and astrophysical uncertainties. The BOSS transmission PDFs, measured at $langle z rangle = [2.3,2.6,3.0]$, are compared with PDFs created from mock spectra drawn from a suite of hydrodynamical simulations that sample the IGM temperature-density relationship, $gamma$, and temperature at mean-density, $T_0$, where $T(Delta) = T_0 Delta^{gamma-1}$. We find that a significant population of partial Lyman-limit systems with a column-density distribution slope of $beta_mathrm{pLLS} sim -2$ are required to explain the data at the low-transmission end of transmission PDF, while uncertainties in the mean Ly$alpha$ forest transmission affect the high-transmission end. After modelling the LLSs and marginalizing over mean-transmission uncertainties, we find that $gamma=1.6$ best describes the data over our entire redshift range, although constraints on $T_0$ are affected by systematic uncertainties. Within our model framework, isothermal or inverted temperature-density relationships ($gamma leq 1$) are disfavored at a significance of over 4$sigma$, although this could be somewhat weakened by cosmological and astrophysical uncertainties that we did not model.
The Lyman-$alpha$ forest is a highly non-linear field with a lot of information available in the data beyond the power spectrum. The flux probability distribution function (PDF) has been used as a successful probe of small-scale physics. In this paper we argue that measuring coefficients of the Legendre polyonomial expansion of the PDF offers several advantages over measuring the binned values as is commonly done. In particular, $n$-th coefficient can be expressed as a linear combination of the first $n$ moments, allowing these coefficients to be measured in the presence of noise and allowing a clear route for marginalisation over mean flux. Moreover, in the presence of noise, our numerical work shows that a finite number of coefficients are well measured with a very sharp transition into noise dominance. This compresses the available information into a small number of well-measured quantities. We find that the amount of recoverable information is a very non-linear function of spectral noise that strongly favors fewer quasars measured at better signal to noise.
We examine the cosmological information available from the 1-point probability distribution (PDF) of the weak-lensing convergence field, utilizing fast L-PICOLA simulations and a Fisher analysis. We find competitive constraints in the $Omega_m$-$sigma_8$ plane from the convergence PDF with $188 arcmin^2$ pixels compared to the cosmic shear power spectrum with an equivalent number of modes ($ell < 886$). The convergence PDF also partially breaks the degeneracy cosmic shear exhibits in that parameter space. A joint analysis of the convergence PDF and shear 2-point function also reduces the impact of shape measurement systematics, to which the PDF is less susceptible, and improves the total figure of merit by a factor of $2-3$, depending on the level of systematics. Finally, we present a correction factor necessary for calculating the unbiased Fisher information from finite differences using a limited number of cosmological simulations.
We propose a new method for fitting the full-shape of the Lyman-$alpha$ (Ly$alpha$) forest three-dimensional (3D) correlation function in order to measure the Alcock-Paczynski (AP) effect. Our method preserves the robustness of baryon acoustic oscillations (BAO) analyses, while also providing extra cosmological information from a broader range of scales. We compute idealized forecasts for the Dark Energy Spectroscopic Instrument (DESI) using the Ly$alpha$ auto-correlation and its cross-correlation with quasars, and show how this type of analysis improves cosmological constraints. The DESI Ly$alpha$ BAO analysis is expected to measure $H(z_mathrm{eff})r_mathrm{d}$ and $D_mathrm{M}(z_mathrm{eff})/r_mathrm{d}$ with a precision of $sim0.9%$ each, where $H$ is the Hubble parameter, $r_mathrm{d}$ is the comoving BAO scale, $D_mathrm{M}$ is the comoving angular diameter distance and the effective redshift of the measurement is $z_mathrm{eff}simeq2.3$. By fitting the AP parameter from the full shape of the two correlations, we show that we can obtain a precision of $sim0.5-0.6%$ on each of $H(z_mathrm{eff})r_mathrm{d}$ and $D_mathrm{M}(z_mathrm{eff})/r_mathrm{d}$. Furthermore, we show that a joint full-shape analysis of the Ly$alpha$ auto-correlation and its cross-correlation with quasars can measure the linear growth rate times the amplitude of matter fluctuations in spheres of $8;h^{-1}$Mpc, $fsigma_8(z_mathrm{eff})$. Such an analysis could provide the first ever measurement of $fsigma_8(z_mathrm{eff})$ at redshift $z_mathrm{eff}>2$. By combining this with the quasar auto-correlation in a joint analysis of the three high-redshift two-point correlation functions, we show that DESI could be able to measure $fsigma_8(z_mathrm{eff}simeq2.3)$ with a precision of $5-12%$, depending on the smallest scale fitted.
The Lyman-$alpha$ forest is a valuable probe of dark matter models featuring a scale-dependent suppression of the power spectrum as compared to $Lambda$CDM. In this work, we present a new estimator of the Lyman-$alpha$ flux power spectrum that does not rely on hydrodynamical simulations. Our framework is characterized by nuisance parameters that encapsulate the complex physics of the intergalactic medium and sensitivity to highly non-linear small-scale modes. After validating the approach based on high-resolution hydrodynamical simulations for $Lambda$CDM, we derive conservative constraints on interacting dark matter models from BOSS Lyman-$alpha$ data on large scales, k<0.02(km/s)^(-1), with the relevant nuisance parameters left free in the model fit. The estimator yields lower bounds on the mass of cannibal dark matter, where freeze-out occurs through 3-to-2 annihilation, in the MeV range. Furthermore, we find that models of dark matter interacting with dark radiation, which have been argued to address the $H_0$ and $sigma_8$ tensions, are compatible with BOSS Lyman-$alpha$ data.
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