Did Massive Primordial Stars Preenrich the Lyman Alpha Forest?

We examine the dynamical evolution and statistical properties of the supernova ejecta of massive primordial stars in a cosmological framework to determine whether this first population of stars could have enriched the universe to the levels and dispersions seen by the most recent observations of the Lyman-Alpha forest. We evolve a lambda CDM model in a 1 Mpc^3 volume to a redshift of z = 15 and add ``bubbles'' of metal corresponding to the supernova ejecta of the first generation of massive stars in all dark matter halos with masses greater than 5 times 10^5 solar masses. These initial conditions are then evolved to z = 3 and the distribution and levels of metals are compared to observations. In the absence of further star formation the primordial metal is initially contained in halos and filaments. Photoevaporation of metal-enriched gas due to the metagalactic ultraviolet background radiation at the epoch of reionization (z ~ 6) causes a sharp increase of the metal volume filling factor. At z = 3, ~ 2.5% of the simulation volume (approx. 20% of the total gas mass) is filled with gas enriched above a metallicity of 10^-4 Z_solar, and less than 0.6% of the volume is enriched above a metallicity of 10^-3 Z_solar. This suggests that, even with the most optimistic prescription for placement of primordial supernova and the amount of metals produced by each supernova, this population of stars cannot entirely be responsible for the enrichment of the Lyman-$\alpha$ forest to the levels and dispersions seen by current observations unless we have severely underestimated the duration of the Pop III epoch. However, comparison to observations show that Pop III supernovae can be significant contributors to the very low overdensity Lyman-Alpha forest.Comment: 4 pages, 3 figures (color). Accepted to ApJ Letters. Replaced version has some correction

A Statistical Analysis of Intergalactic Medium Transmission Approaching Reionization

We use hydrodynamic cosmological simulations in a 9.6 Mpc box to explore the evolution of the intergalactic medium (IGM) transmissivity from z=2 through the epoch of reionization. Reionization is achieved through an ultraviolet background (UVB) that includes evolving stellar and QSO source populations. We construct and analyze noiseless synthetic HI Lya absorption spectra along lines of sight through our continuously evolving box and find a smooth evolution of the effective optical depth under a power law up to the epoch of reionization. Crossing into the epoch of reionization, both the mean transmitted flux (MTF) and variance to the mean transmitted flux sharply deviate from a smooth evolution and hence such observables have large margins of error. Despite the statistical uncertainty in inferring the reionization profile from spectra, the end of an opacity phase transition of the IGM correlates well with the redshift when both the mean and variance of the transmitted flux rapidly deviate from the post-reionization profile. However, an unobtainable number of lines of sight is needed to allow an estimate of the MTF with less than 10% relative margin of error. In addition to optical transmission, we compare the predicted dark gap length distribution with observations. We show that this statistic is sensitive to spectral resolution at reionization redshifts, but overall in agreement with results by Songaila and Cowie (2002). Finally, we derive a positive correlation between the mean optical depth within a gap and the size of the gap, in attempt to relate "transmission statistics" to "dark gap statistics" in high redshift studies of the IGM.Comment: 53 pages, 24 figure

Cosmological parameters sigma_8, the baryon density, and the UV background intensity from a calibrated measurement of H I Lyman-alpha absorption at z = 1.9

We identify a concordant model for the intergalactic medium (IGM) at redshift z=1.9 that uses popular values for cosmological and astrophysical parameters and accounts for all baryons with an uncertainty of 6%. We have measured the amount of absorption, DA, in the Ly-alpha forest at redshift 1.9 in spectra of 77 QSO from the Kast spectrograph. We calibrated the continuum fits with realistic artificial spectra, and we found that averaged over all 77 QSOs the mean continuum level is within 1-2% of the correct value. Absorption from all lines in the Ly-alpha forest at z=1.9 removes DA=15.1 +/- 0.7% of the flux between 1070 and 1170 (rest) Angstroms. This is the first measurement using many QSOs at this z, and the first calibrated measurement at any redshift. Metal lines absorb 2.3 +/- 0.5%, and LLS absorb 1.0 +/- 0.4% leaving 11.8 +/- 1.0% from the lower density bulk of the IGM. Averaging over Delta z=0.1 or 154 Mpc, the dispersion is 6.1 +/- 0.3% including LLS and metal lines, or 3.9 (+0.5, -0.7)% for the lower density IGM alone, consistent with the usual description of large scale structure. LLS and metal lines are major contributors to the variation in the mean flux, and they make the flux field significantly non-Gaussian. We find that a hydrodynamic simulation on a 1024 cubed grid in a 75.7 Mpc box reproduces the observed DA from the low density IGM with parameters values H_o=71 km/s/Mpc, Omega_Lambda=0.73, Omega_m=0.27, Omega_b=0.044, sigma_8=0.9 and a UV background that has an ionization rate that is 1.08 +/- 0.08 times the prediction by Madau, Haardt & Rees (1999).Comment: Submitted to Ap

Creating a content delivery network for general science on the internet backbone using XCaches

A general problem faced by computing on the grid for opportunistic users is that delivering cycles is simpler than delivering data to those cycles. In this project we show how we integrated XRootD caches placed on the internet backbone to implement a content delivery network for general science workflows. We will show that for some workflows on different science domains like high energy physics, gravitational waves, and others the combination of data reuse from the workflows together with the use of caches increases CPU efficiency while decreasing network bandwidth use

The Lyman-alpha forest at redshifts 0.1 -- 1.6: good agreement between a large hydrodynamic simulation and HST spectra

We give a comprehensive statistical description of the Lyman-alpha absorption from the intergalactic medium in a hydrodynamic simulation at redshifts 0.1-1.6, the range of redshifts covered by HST spectra of QSOs. We use the ENZO code to make a 76 comoving Mpc cube simulation using 75 kpc cells, for a Hubble constant of 71 km/s/Mpc. The best prior work, by \citet{dave99},used an SPH simulation in a 15.6 Mpc box with an effective resolution of 245 kpc and slightly different cosmological parameters. At redshifts z=2 this simulation is different from data. \citet{tytler07b} found that the simulated spectra at z=2 have too little power on large scales, Lyman-alpha lines are too wide, there is a lack high column density lines, and there is a lack of pixels with low flux. Here we present statistics at z<1.6, including the flux distribution, the mean flux, the effective opacity, and the power and correlation of the flux. We also give statistics of the lyman alpha lines including the line width distribution, the column density distribution, the number of lines per unit equivalent width and redshift, and the correlation between the line width and column density. We find that the mean amount of absorption in the simulated spectra changes smoothly with redshift with DA(z)=0.01(1+z)^{2.25}. Both the trend and absolute values are close to measurements of HST spectra by \citet{kirkman07a}. The column density and line width distributions are also close to those measured from HST spectra by \citet{janknecht06a}, except for the mode of the line width distribution which is smaller in the HST spectra. Although some differences that we saw at z=2 are too subtle to be seen in existing HST spectra, overall, the simulation gives an good description of HST spectra at 0.1<z<1.6

The Effect of Large-Scale Power on Simulated Spectra of the Lya forest

We study the effects of box size on ENZO simulations of the intergalactic medium (IGM) at z = 2. We follow statistics of the cold dark matter (CDM) and the Lya absorption. We find that the larger boxes have fewer pixels with significant absorption (flux < 0.96) and more pixels in longer stretches with little or no absorption, and they have wider Lya lines. We trace these effect back to the additional power in larger boxes from longer wavelength modes. The IGM in our larger boxes is hotter, from increased pressure heating due to faster hydrodynamical infall. When we increase the photoheating in smaller boxes to compensate, their Lya statistics change to mimic those of a box of twice the size. Statistics converge towards their value in the largest (76.8 Mpc) box, except for the most common value of the CDM density which continues to rise. When we compare to errors with data, we find that our 76.8 Mpc box is larger than we need for the mean flux, barely large enough for the column density distribution and the power spectrum of the flux, and too small for the line widths. This box with 75 kpc cells has approximately the same mean flux as QSO spectra, but the Lya lines are too wide by 2.6 km/s, there are too few lines with log H I column densities > 10^17 cm^-2, and the power of the flux is too low by 20 - 50%, from small to large scales. Four times smaller cell size does not resolve these differences, nor do simple changes to the ultraviolet background that drives the H and He II ionization. It is hard to see how simulations using popular cosmological and astrophysical parameters can match Lyman-alpha forest data at z=2

H I gas in higher density regions of the intergalactic medium

Using H I absorption alone, we attempt to separate H I absorption lines in quasar spectra into two categories; HDLs (Higher Density Lines) and LDLs (Lower Density Lines), and we discuss the difference in their physical properties. We deblend and fit all H I lines with Voigt profiles, and make an unbiased sample of H I lines covering a wide column density range (12 < log N_HI < 19 cm^-2). To reduce the influence of line blending, we simultaneously fit several Lyman series lines. As a result of a two-point correlation analysis, we found that higher column density H I lines are clustering at $\Delta$ v < 200 km/s, while lower ones at $\Delta$ v < 100 km/s. We define HDLs as H I lines with 15 < log N_HI 15 cm^-2, and LDLs as others with 12 < log N_HI < 15 cm^-2. We found that the HDLs have smaller minimum b-values for a given column density than the LDLs. This difference is successfully reproduced by our Hydrodynamic simulation. The LDLs seem to be cool or shock-heated diffuse IGM gas, while the HDLs are likely to be cooler dense gas near to galaxies.Comment: 22 pages, 7 figures, accepted for publication in the Astronomical Journa

Background Monte Carlo Samples for a Future Hadron Collider

A description of Standard Model background Monte Carlo samples produced for studies related to future hadron colliders