Forêt Lyman-α

Résumé

En cosmologie, la forêt Lyman-α désigne l'ensemble des structures observées dans les spectres des galaxies et quasars lointains, et qui sont dues à l'absorption par le milieu intergalactique d'une partie de la lumière émise par ces objets. Les photons absorbés sont ceux qui permettent une transition entre différents états excités de l'hydrogène neutre (non ionisé), partant de son état fondamental, ce qui correspond en spectroscopie à ce que l'on appelle la série de Lyman. En pratique, c'est surtout la transition vers le premier état excité qui est observée, ce qui correspond à la raie Lyman-α. Par ailleurs, les structures observées dans les spectres révèlent une abondance très élevée de ces raies d'absorption, correspondant à des absorbeurs répartis à différentes distances sur la ligne de visée, d'où le terme de « forêt ». Classification La profondeur d'une raie d'absorption dépend à la fois de la densité de la structure qui cause l'absorption et de sa taille. En pratique,

Source officielle

https://fr.wikipedia.org/wiki/For%C3%AAt_Lyman-%CE%B1

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (23)

Publications associées

Chargement

Personnes associées (5)

Personnes associées

Chargement

Unités associées (3)

Unités associées

Chargement

Concepts associés (11)

Concepts associés

Chargement

Cours associés (2)

Cours associés

Chargement

Séances de cours associées (8)

Séances de cours associées

Chargement

Neutrino masses and cosmology with Lyman-alpha forest power spectrum

Arnaud Borde, Julien Lesgourgues

We present constraints on neutrino masses, the primordial fluctuation spectrum from inflation, and other parameters of the ACDM model, using the one-dimensional Ly alpha-forest power spectrum measured by [1] from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III), complemented by Planck 2015 cosmic microwave background (CMB) data and other cosmological probes. This paper improves on the previous analysis by [2] 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 Sigma m(nu) < 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-toscalar ratio of primordial fluctuations r. The tension on n(s) can be accommodated by allowing for a running dn(s)/d In k. Allowing running as a free parameter in the fits does not change the limit on Sigma m(nu). We discuss possible interpretations of these results in the context of slow-roll inflation.

Iop Publishing Ltd2015

Chargement

We present constraints on the parameters of the ACDM cosmological model in the presence of massive neutrinos, using the one-dimensional Ly alpha forest power spectrum obtained with the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS) by Palanque-Delabrouille et al. [1], complemented by additional cosmological probes. The interpretation of the measured Ly alpha spectrum is done using a second-order Taylor expansion of the simulated power spectrum. BOSS Ly alpha data alone provide better bounds than previous Ly alpha results, but are still poorly constraining, especially for the sum of neutrino masses Sigma m(v), for which we obtain an upper bound of 1.1 eV (95% CL), including systematics for both data and simulations. Ly alpha constraints on ACDM parameters and neutrino masses are compatible with CMB bounds from the Planck collaboration [2]. Interestingly, the combination of Ly alpha with CMB data reduces the uncertainties significantly, due to very different directions of degeneracy in parameter space, leading to the strongest cosmological bound to date on the total neutrino mass, Sigma m(v) < 0.15 eV at 95% CL (with a best-fit in zero). Adding recent BAO results further tightens this constraint to Sigma m(v) < 0.14 eV at 95% CL. This bound is nearly independent of the statistical approach used, and of the different combinations of CMB and BAO data sets considered in this paper in addition to Ly alpha. Given the measured values of the two squared mass differences Delta m(2), this result tends to favor the normal hierarchy scenario against the inverted hierarchy scenario for the masses of the active neutrino species.

Iop Publishing Ltd2015

Chargement

Measurement of baryon acoustic oscillation correlations at z=2.3 with SDSS DR12 Ly alpha-Forests

Timothée Guy Olivier Delubac

Here, we use flux-transmission correlations in Ly alpha forests to measure the imprint of baryon acoustic oscillations (BAO). The study uses spectra of 157,783 quasars in the redshift range 2.1

Edp Sciences S A2017

Chargement