Light-cone anisotropy in 21 cm fluctuations simulated with the Licorice code

Poster presented at the workshop "The Epoch of Reionization: Theory - Simulations - Observations". Strasbourg, France 23-27 April 2012. http://sci.esa.int/jump.cfm?oid=50204One of the possible sources of an anisotropy in the power spectrum of 21 cm brightness fluctuations from the epoch of reionization is the delay in light traveltime along the line-of-sight. We examine the anisotropy between the parallel and transverse directions with respect to the line-of-sight with the LICORICE code. Based on Barkana & Loeb (2006) approach we study the time-delay effect in the realistic numerical simulations of the epoch of reionization

Cosmological radiative transfer comparison project - II. The radiation-hydrodynamic tests

The development of radiation hydrodynamical methods that are able to follow gas dynamics and radiative transfer (RT) self-consistently is key to the solution of many problems in numerical astrophysics. Such fluid flows are highly complex, rarely allowing even for approximate analytical solutions against which numerical codes can be tested. An alternative validation procedure is to compare different methods against each other on common problems, in order to assess the robustness of the results and establish a range of validity for the methods. Previously, we presented such a comparison for a set of pure RT tests (i.e. for fixed, non-evolving density fields). This is the second paper of the Cosmological Radiative Transfer Comparison Project, in which we compare nine independent RT codes directly coupled to gas dynamics on three relatively simple astrophysical hydrodynamics problems: (i) the expansion of an H ii region in a uniform medium, (ii) an ionization front in a 1/r2 density profile with a flat core and (iii) the photoevaporation of a uniform dense clump. Results show a broad agreement between the different methods and no big failures, indicating that the participating codes have reached a certain level of maturity and reliability. However, many details still do differ, and virtually every code has showed some shortcomings and has disagreed, in one respect or another, with the majority of the results. This underscores the fact that no method is universal and all require careful testing of the particular features which are most relevant to the specific problem at han

Radiative Flux and Forcing Parameterization Error in Aerosol-Free Clear Skies

This article reports on the accuracy in aerosol- and cloud-free conditions of the radiation parameterizations used in climate models. Accuracy is assessed relative to observationally validated reference models for fluxes under present-day conditions and forcing (flux changes) from quadrupled concentrations of carbon dioxide. Agreement among reference models is typically within 1 W/m2, while parameterized calculations are roughly half as accurate in the longwave and even less accurate, and more variable, in the shortwave. Absorption of shortwave radiation is underestimated by most parameterizations in the present day and has relatively large errors in forcing. Error in present-day conditions is essentially unrelated to error in forcing calculations. Recent revisions to parameterizations have reduced error in most cases. A dependence on atmospheric conditions, including integrated water vapor, means that global estimates of parameterization error relevant for the radiative forcing of climate change will require much more ambitious calculations

Simulation de l'époque de la réionisation : transfert radiatif

The 21-cm hyperfine line of neutral hydrogen from the high-redshift Universe (6 In this work, we develop a continuum radiative transfer part for the LICORICE cosmological code to study the epoch of reionization, where radiative transfer is an essential tool. We use a Monte-Carlo ray-tracing algorithm on an adaptive grid. Several tests, both for static density field cases and radiative hydrodynamic cases have been performed to validate the code.Then we compute the 21-cm signal during the EoR, which provides a direct probe on reionization and contains a lot of informations on the sources of ionization and heating. Usually the Ly-α flux, which influences the strength of the 21-cm signal, is assumed to be strong and homogeneous during the whole cosmic reionization, but this assumption is not valid during the early stage of EoR. We evaluate exactly the local Ly-α flux using the Lyman line radiative transfer module of LICORICE and show that using the local Ly-α flux modifies the power spectrum of the 21-cm signal, especially during the early reionization. We also find a strong signal in absorption which can not be predicted with the usual assumptions. Even a small amount of X-rays can affect the physical state of the neutral inter galactic medium since X-rays have a very long mean free path. X-ray heating is an important factor to evaluate the strength of the 21-cm signal in the neutral regions, so we implemented the corresponding ray-tracing in LICORICE. We find that X-rays need time to increase the gas temperature in the IGM above the CMB temperature, so with a reasonable level of X-rays we can still see the signal in strong absorption during the early phase of reionization.In addition, we study the formation of galaxies in a cosmological context. The goal is to explore the physics of primordial galaxies considering radiative feedback on hydrodynamics. In a preliminary way, we find that including non-equilibrium ionization modifies the temperature of the diffuse gas, and its accretion history.La raie hyperfine à 21-cm de l'hydrogène atomique émise dans l'univers à grand redshift (6 Dans ce travail, nous avons développé un module de transfert radiatif pour le continuum ionisant dans le code LICORICE dans le but de simuler l'époque de la réionisation, pour laquelle le transfert radiatif est un outil essentiel. Nous utilisons un algorithme de ray-tracing de type Monte Carlo sur une grille adaptative. Plusieurs tests sont réalisés pour valider le code dans deux cas, celui d'un champ de densité statique et dans le cas de l'hydrodynamique radiative. Nous produisons ensuite le signal à 21-cm émis pendant l'EoR, qui nous fournit une sonde directe de la réionisation et contient de nombreuses informations sur les sources d'ionisation et de chauffage. Habituellement, on suppose que le flux Ly-α, qui influence la puissance du signal à 21-cm, est fort et homogéne pendant toute la réionisation, mais cette hypothèse n'est pas valable durant la première phase de l'EoR. Nous évaluons exactement le flux Ly-α local en utilisant le module de transfert radiatif de la raie Lyman α et montrons que ce flux modifie le spectre de puissance du signal à 21-cm, particuliérement pendant la première phase de la réionisation. Nous trouvons également que le signal est en absorption forte ce qui ne peut pas être simulé avec les hypothèses habituelles. Même une faible quantité de rayons X peut affecter l'état physique du gaz neutre dans le milieu inter galactique, puisque ceux-ci ont un libre parcours moyen très long. Le chauffage par les rayons X est un facteur important pour évaluer la puissance du signal à 21-cm dans les régions neutres, aussi avons nous inclus le ray-tracing correspondant dans LICORICE. Nous constatons que les rayons X ont besoin de temps pour élever la température du gaz au-dessus de la température du CMB. Ainsi, avec un niveau de rayons X raisonnable, nous continuons à observer le signal en absorption pendant la premi`ere phase de la réionisation.De plus, nous étudions la formation des galaxies dans un contexte cosmologique. Le but est d'explorer la physique des galaxies primordiales en considérant la rétroaction radiative sur l'hydrodynamique. Nos résultats préliminaires montrent que le calcul de l'ionisation hors équilibre modifie la température du gaz diffus, et son histoire d'accrétion

Simulation of the epoch of reionization (radiative transfer)

La raie hyperfine à 21-cm de l hydrogène atomique émise dans l univers à grand redshift (6 < z < 20) permetra de sonder une nouvell ère de la cosmologie, l époque de la réionisation (EoR). Les radio télescopes de nouvelle génération, SKA et ses précurseurs, entreront en service dans les prochaines années pour observer ce signal. La simulation numérique du 21-cm est importante pour optimiser le design des instruments et interpréter les observations futures. Nous avons développé un module de transfert radiatif dans le code LICORICE. Nous produisons ensuite le signal à 21-cm émis pendant l EoR. Nous évaluons le flux Ly- local et montrons que ce flux modifie le spectre de puissance du signal. Nous trouvons également que le signal est en absorption forte ce qui ne peut pas être simulé avec les hypothèses habituelles. Nous constatons que les rayons X ont besoin de temps pour élever la température du gaz au-dessus de la température du CMB. Ainsi, avec un niveau de rayons X raisonnable, nous continuons à observer le signal en absorption pendant la première phase de la réionisation. De plus, nous étudions la formation des galaxies dans un contexte cosmologique.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Light-cone anisotropy in the 21 cm signal from the epoch of reionization

International audienc

Radiative flux and forcing parameterization error in aerosol-free clear skies

This article reports on the accuracy in aerosol- and cloud-free conditions of the radiation parameterizations used in climate models. Accuracy is assessed relative to observationally validated reference models for fluxes under present-day conditions and forcing (flux changes) from quadrupled concentrations of carbon dioxide. Agreement among reference models is typically within 1 W/m(2), while parameterized calculations are roughly half as accurate in the longwave and even less accurate, and more variable, in the shortwave. Absorption of shortwave radiation is underestimated by most parameterizations in the present day and has relatively large errors in forcing. Error in present-day conditions is essentially unrelated to error in forcing calculations. Recent revisions to parameterizations have reduced error in most cases. A dependence on atmospheric conditions, including integrated water vapor, means that global estimates of parameterization error relevant for the radiative forcing of climate change will require much more ambitious calculations