Jordi Miralda-Escudé

Reionization of the Inhomogeneous Universe

A model of the density distribution in the intergalactic medium (IGM), motivated by that found in numerical simulations, is used to demonstrate the effect of a clumpy IGM and discrete sources on the reionization of the universe. In an inhomogeneous universe reionization occurs outside-in, starting in voids and gradually penetrating into overdense regions. Reionization should not be sudden but gradual, with a continuous rise of the photon mean free path over a fair fraction of the Hubble time as the emissivity increases. We show that a hydrogen Gunn-Peterson trough should be present at z 6 unless the emissivity increases with redshift at z > 4. However, the epoch of overlap of cosmological H II regions could have occurred at a higher redshift if sources of low luminosity reionized the IGM; the Gunn-Peterson trough at z ~ 6 would then appear because even the most underdense voids have a large enough neutral fraction in ionization equilibrium to be optically thick to Lyα photons. Cosmological H II regions near the epoch of overlap can produce gaps of transmitted flux only if luminous quasars contributed to the reionization, producing large H II regions. Despite the clumpiness of the matter distribution, recombinations do not increase the required emissivity of ionizing photons by a large factor during the reionization of hydrogen because the high-density gas is not ionized until a late time. We show that the He II reionization was most likely delayed relative to the hydrogen reionization but was probably complete by z ~ 3 (the redshift where observations are available). The reported large optical depth fluctuations of He II are not necessarily due to an incomplete He II reionization but can arise from a combination of IGM density fluctuations and variations in the intensity of the He II ionizing background due to luminous QSOs.

The Lyα Forest from Gravitational Collapse in the Cold Dark Matter + Λ Model

We use an Eulerian hydrodynamic cosmological simulation to model the Ly? forest in a spatially flat, COBE-normalized, cold dark matter model with) ? = 0.4. We find that the intergalactic, photoionized gas is predicted to collapse into sheetlike and filamentary structures which give rise to absorption lines having characteristics similar to the observed Ly? forest. A typical filament is ~500 h?1 kpc long with thickness ~50 h?1 kpc (in proper units), and baryonic mass ~ 1010 h?1 M. In comparison our cell size is (2.5, 9) h?1 kpc in the two simulations we perform, with true resolution perhaps a factor of 2.5 worse than this. The gas temperature is in the range 104-105 K, and it increases with time as structures with larger velocities collapse gravitationally. We show that the predicted distributions of column densities, b-parameters, and equivalent widths of the Ly? forest clouds agree reasonably with observations, and that their evolution is consistent with the observed evolution, if the ionizing background has an approximately constant intensity between z = 2 and z = 4. A new method of identifying lines as contiguous regions in the spectrum below a fixed flux threshold is suggested to analyze the absorption lines, given that the Ly? spectra arise from a continuous density field of neutral hydrogen rather than discrete clouds. We also predict the distribution of transmitted flux and its correlation along a spectrum and on parallel spectra, and the He ii flux decrement as a function of redshift. We predict a correlation length of ~80 h?1 kpc perpendicular to the line of sight for features in the Ly? forest. In order to reproduce the observed number of lines and average flux transmission, the baryon content of the clouds may need to be significantly higher than in previous models because of the low densities and large volume-filling factors we predict. If the background intensity JH I is at least that predicted from the observed quasars, ?b needs to be as high as ~0.25 h?2. The model also predicts that most of the baryons at z > 2 are in Ly? clouds, and that the rate at which the baryons move to more overdense regions is slow. A large fraction of the baryons which are not observed at present in galaxies might be intergalactic gas in the currently collapsing structures, with T ~ 105?106 K. All our results on the statistical properties of the simulated spectra are predictions that can be directly tested by applying the same methods to observed spectra. We are making the simulated spectra electronically available.

The Opacity of the Lyα Forest and Implications for Ωb and the Ionizing Background

We have measured the distribution function of the flux decrement D = 1 - e-τ caused by Lyα forest absorption from intervening gas in the lines of sight to high-redshift QSOs from a sample of seven high-resolution QSO spectra obtained with the Keck telescope. The observed flux decrement distribution function (FDDF) is compared with the FDDF from two simulations of the Lyα forest: a ΛCDM model (with Ω = 0.4, Λ = 0.6), computed with the Eulerian code of Cen & Ostriker, and a standard cold dark matter (SCDM) model (with Ω = 1), computed with the smoothed particle hydrodynamics code of Hernquist et al. Good agreement is obtained between the shapes of the simulated and observed FDDFs for both simulations after fitting only one free parameter, which controls the mean flux decrement. The difference between the predicted FDDFs from the two simulations is small, and we show that it arises mostly from a different temperature in the low-density gas (caused by different assumptions that were made about the reionization history in the two simulations), rather than differences between the two cosmological models or numerical effects in the two codes, which use very different computational methods. A measurement of the parameter μΩ -->2b h -->3/Γ (where Γ is the H I ionization rate due to the ionizing background) is obtained by requiring the mean flux decrement in the simulations to agree with the observed one. Estimating the lower limit Γ > 7 × 10-13 s-1 from the abundance of known QSOs, we derive a lower limit on the baryonic matter density, Ωbh2 > 0.021 (0.017) for the ΛCDM (SCDM) model. The difference between the lower limits inferred from the two models is again due to different temperatures in the low-density gas. We give general analytical arguments for why this lower limit is unlikely to be reduced for any other models of structure formation by gravitational collapse that can explain the observed Lyα forest. When combined with constraints from big bang nucleosynthesis, the large Ωb we infer is inconsistent with some recent D/H determinations (Rugers & Hogan), favoring a low deuterium abundance as reported by Tytler, Fan & Burles. Adopting a fixed Ωb, the measurement of μ(z) allows a determination of the evolution of the ionizing radiation field with redshift. Our models predict an intensity that is approximately constant with redshift, which is in agreement with the assumption that the ionizing background is produced by known quasars for z < 3, but requires additional sources of ionizing photons at higher redshift given the observed rapid decline of the quasar abundance.

Baryon acoustic oscillations in the Lyα forest of BOSS DR11 quasars

We report a detection of the baryon acoustic oscillation (BAO) feature in the flux-correlation function of the Ly forest of high-redshift quasars with a statistical significance of five standard deviations. The study uses 137,562 quasars in the redshift range 2:1 z 3:5 from the Data Release 11 (DR11) of the Baryon Oscillation Spectroscopic Survey (BOSS) of SDSS-III. This sample contains three times the number of quasars used in previous studies. The measured position of the BAO peak determines the angular distance, DA(z = 2:34) and expansion rate, H(z = 2:34), both on a scale set by the sound horizon at the drag epoch, rd. We find DA=rd =

The Observed Probability Distribution Function, Power Spectrum, and Correlation Function of the Transmitted Flux in the Lyα Forest*

A sample of eight quasars observed at high resolution and signal-to-noise ratio is used to determine the transmitted flux probability distribution function (TFPDF), and the power spectrum and correlation function of the transmitted flux in the Lyα forest, in three redshift bins centered at z = 2.41, 3.00, and 3.89. All the results are presented in tabular form, with full error covariance matrices, to allow for comparisons with any numerical simulations and with other data sets. The observations are compared with a numerical simulation of the Lyα forest of a ΛCDM model with Ω = 0.4, known to agree with other large-scale structure observational constraints. There is excellent agreement for the TFPDF if the mean transmitted flux is adjusted to match the observations. A small difference between the observed and predicted TFPDF is found at high fluxes and low redshift, which may be due to the uncertain effects of fitting the spectral continuum. Using the numerical simulation, we show how the flux power spectrum can be used to recover the initial power spectrum of density fluctuations. From our sample of eight quasars, we measure the amplitude of the mass power spectrum to correspond to a linear variance per unit ln k of Δ(k) = 0.72 ± 0.09 at k = 0.04(km s-1)-1 and z = 3, and the slope of the power spectrum near the same k to be np = -2.55 ± 0.10 (statistical error bars). The results are statistically consistent with those of Croft et al., although our value for the rms fluctuation is lower by a factor of 0.75. For the ΛCDM model we use, the implied primordial slope is n = 0.93 ± 0.10, and the normalization is σ8 = 0.68 + 1.16(0.95 - n) ± 0.04.

Reionization of the Intergalactic Medium and the Damping Wing of the Gunn-Peterson Trough

Observations of high-redshift quasars show that the intergalactic medium (IGM) must have been reionized at some redshift z > 5. If a source of radiation could be observed at the rest-frame Lyα wavelength, at a sufficiently high redshift where some of the IGM in the line of sight was not yet reionized, the Gunn-Peterson trough should be present. Longward of the Lyα wavelength, a damping wing should be observed, caused by the neutral IGM whose absorption profile can be predicted. Measuring the shape of this damping wing would provide irrefutable evidence of the observation of the IGM before reionization and a determination of the density of the neutral IGM. This measurement might be hindered by the possible presence of a dense absorption system associated with the source. Shortward of the Lyα wavelength, absorption should be seen from the patchy structure of the IGM in the process of reionization, intersected in the line of sight. We show that a complete Gunn-Peterson trough is most likely to continue to be observed through the epoch where the IGM is partially ionized. The damping wings of the neutral patches around an ionized region should overlap in the spectrum if the proper path length through the ionized region is less than 1 h-1 Mpc; even in larger ionized regions, the characteristic background intensity should be low enough to yield a very high optical depth due to the residual neutral fraction, although occasionally some flux may be transmitted through large, underdense voids within an ionized region. In the case of the He II reionization, the ionization fronts are much thicker than in the case of hydrogen, and the profile of this front determines the shape of the absorption at the edge of a He III region. Analogous to the case of hydrogen, windows of transmitted flux are not likely to be observed until after the low-density IGM has been completely reionized. Therefore, the observation of these transmission windows by Reimers et al. at z 2.85 suggests that the helium reionization was complete by this redshift. The recently discovered afterglows of gamma-ray bursts might soon be observed at the very high redshifts required for these observations. Their featureless continuum spectrum and high luminosities make them ideal sources for studying absorption by the IGM.

Column density distribution and cosmological mass density of neutral gas: Sloan Digital Sky Survey-III Data Release 9

We present the first results from an ongoing survey for damped Lyman-α systems (DLAs) in the spectra of z > 2 quasars observed in the course of the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the Sloan Digital Sky Survey (SDSS) III. Our full (non-statistical) sample, based on Data Release 9, comprises 12 081 systems with log N(Hi) ≥ 20, out of which 6839 have logN(Hi) ≥ 20.3. This is the largest DLA sample ever compiled, superseding that from SDSS-II by a factor of seven.

The Sloan Digital Sky Survey quasar catalog: ninth data release

We present the Data Release 9 Quasar (DR9Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. The catalog includes all BOSS objects that were targeted as quasar candidates during the survey, are spectrocopically confirmed as quasars via visual inspection, have luminosities Mi[z = 2] 2.15 (61 931) is ~2.8 times larger than the number of z > 2.15 quasars previously known. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C iii], Mg ii). The catalog identifies 7533 broad absorption line quasars and gives their characteristics. For each object the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3600−10 500 A at a spectral resolution in the range 1300 < R < 2500; the spectra can be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 949 quasars that have been identified, among galaxy targets of the BOSS or among quasar targets after DR9 was frozen.

ORBITAL PERTURBATIONS OF TRANSITING PLANETS: A POSSIBLE METHOD TO MEASURE STELLAR QUADRUPOLES AND TO DETECT EARTH-MASS PLANETS

The recent discovery of a planetary transit in the star HD 209458, and the subsequent highly precise observation of the transit light curve with Hubble Space Telescope, is encouraging to search for any phenomena that might induce small changes in the light curve. Here we consider the eUect of the quadrupole moment of the parent star and of a possible second planet perturbing the orbit of the transiting planet. Both of these cause a precession of the orbital plane and of the periastron of the planet, which result in a long-term variation of the duration and the period of the transits. For a transiting planet at 0.05 AU, either a quadrupole moment similar to that of the Sun or the gravitational tug from an Earthlike planet on an orbit of semimajor axis D0.2 AU and a relative inclination near the optimal 45i would cause a transit duration time derivative of D 1sy r~1.The recent discovery of a planetary transit in the star HD 209458, and the subsequent highly precise observation of the transit light curve with Hubble Space Telescope, is encouraging to search for any phenomena that might induce small changes in the light curve. Here we consider the effect of the quadrupole moment of the parent star and of a possible second planet perturbing the orbit of the transiting planet. Both of these cause a precession of the orbital plane and of the periastron of the planet, which result in a long-term variation of the duration and the period of the transits. For a transiting planet at 0.05 AU, either a quadrupole moment similar to that of the Sun or the gravitational tug from an Earth-like planet on an orbit of semimajor axis ~0.2 AU and a relative inclination near the optimal 45° would cause a transit duration time derivative of ~1 s yr-1.

Quasar-Lyman α forest cross-correlation from BOSS DR11: Baryon Acoustic Oscillations

Author(s): Font-Ribera, A; Kirkby, D; Busca, N; Miralda-Escude, J; Ross, NP; Slosar, A; Rich, J; Aubourg, E; Bailey, S; Bhardwaj, V; Bautista, J; Beutler, F; Bizyaev, D; Blomqvist, M; Brewington, H; Brinkmann, J; Brownstein, JR; Carithers, B; Dawson, KS; Delubac, T; Ebelke, G; Eisenstein, DJ; Ge, J; Kinemuchi, K; Lee, KG; Malanushenko, V; Malanushenko, E; Marchante, M; Margala, D; Muna, D; Myers, AD; Noterdaeme, P; Oravetz, D; Palanque-Delabrouille, N; Pâris, I; Petitjean, P; Pieri, MM; Rossi, G; Schneider, DP; Simmons, A; Viel, M; Yeche, C; York, DG | Abstract: We measure the large-scale cross-correlation of quasars with the Lyα forest absorption, using over 164,000 quasars from Data Release 11 of the SDSS-III Baryon Oscillation Spectroscopic Survey. We extend the previous study of roughly 60,000 quasars from Data Release 9 to larger separations, allowing a measurement of the Baryonic Acoustic Oscillation (BAO) scale along the line of sight c/(H(z = 2.36)rs) = 9.0±0.3 and across the line of sight DA (z = 2.36)/rs = 10.8±0.4, consistent with CMB and other BAO data. Using the best fit value of the sound horizon from Planck data (rs = 147.49 Mpc), we can translate these results to a measurement of the Hubble parameter of H(z = 2.36) = 226±8 km s -1 Mpc-1 and of the angular diameter distance of D A (z = 2.36) = 1590±60 Mpc. The measured cross-correlation function and an update of the code to fit the BAO scale (baofit) are made publicly available.©2014 IOP Publishing Ltd and Sissa Medialab srl.