Feedback and its Feedback Effect on Feedback: Photoionization Suppression and its Impact on Galactic Outflows

We show that radiative feedback due to reionization has a pronounced effect on the extent of mechanical feedback due to galactic outflows. The photoionization of the Intergalactic Medium (IGM) suppresses low-mass galaxy formation by photoheating the gas and limiting atomic line cooling. The number of low-mass galaxies is central for the enrichment of the IGM as these objects have the capacity to enrich a significant fraction (by volume) of the Universe. We use a modified version of our galactic outflow model, combined with a simple criterion for suppression, to investigate the potential impact upon the IGM. We find that this suppression strongly reduces the enrichment of the IGM and is sensitive to the reionization history. We also investigate the contribution of halos of different masses with varying degrees of suppression.Comment: 4 pages, 3 figures, class file included, accepted by ApJ Letters, minor changes and expanded Figure

Anisotropic Outflows and IGM Enrichment

We have designed an analytical model for the evolution of anisotropic galactic outflows. These outflows follow the path of least resistance, and thus travel preferentially into low-density regions, away from cosmological structures where galaxies form. We show that anisotropic outflows can significantly enrich low-density systems with metals.Comment: Proceedings of Chemodynamics 2006, Lyon, 2 pages, 1 figure, style file include

The Composite Spectrum of Strong Lyman-alpha Forest Absorbers

We present a new method for probing the physical conditions and metal enrichment of the Intergalactic Medium: the composite spectrum of Ly-alpha forest absorbers. We apply this technique to a sample of 9480 Ly-alpha absorbers with redshift 2 < z < 3.5 identified in the spectra of 13,279 high-redshift quasars from the Sloan Digital Sky Survey (SDSS) Fifth Data Release (DR5). Absorbers are selected as local minima in the spectra with 2.4 < tau_Ly-alpha < 4.0; at SDSS resolution (~ 150km/s FWHM), these absorbers are blends of systems that are individually weaker. In the stacked spectra we detect seven Lyman-series lines and metal lines of O VI, N V, C IV, C III, Si IV, C II, Al II, Si II, Fe II, Mg II, and O I. Many of these lines have peak optical depths of < 0.02, but they are nonetheless detected at high statistical significance. Modeling the Lyman-series measurements implies that our selected systems have total H I column densities N_HI ~ 10^15.4cm-2. Assuming typical physical conditions rho / = 10, T = 10^4 - 10^4.5 K, and [Fe/H]= -2 yields reasonable agreement with the line strengths of high-ionization species, but it underpredicts the low-ionization species by two orders of magnitude or more. This discrepancy suggests that the low ionization lines arise in dense, cool, metal-rich clumps, present in some absorption systems.Comment: 7 pages, 4 figures, 1 table, accepted by ApJL, revisions mad

Anisotropic Galactic Outflows and Enrichment of the Intergalactic Medium. I: Monte Carlo Simulations

We have developed an analytical model to describe the evolution of anisotropic galactic outflows. With it, we investigate the impact of varying opening angle on galaxy formation and the evolution of the IGM. We have implemented this model in a Monte Carlo algorithm to simulate galaxy formation and outflows in a cosmological context. Using this algorithm, we have simulated the evolution of a comoving volume of size [12h^(-1)Mpc]^3 in the LCDM universe. Starting from a Gaussian density field at redshift z=24, we follow the formation of ~20,000 galaxies, and simulate the galactic outflows produced by these galaxies. When these outflows collide with density peaks, ram pressure stripping of the gas inside the peak may result. This occurs in around half the cases and prevents the formation of galaxies. Anisotropic outflows follow the path of least resistance, and thus travel preferentially into low-density regions, away from cosmological structures (filaments and pancakes) where galaxies form. As a result, the number of collisions is reduced, leading to the formation of a larger number of galaxies. Anisotropic outflows can significantly enrich low-density systems with metals. Conversely, the cross-pollution in metals of objects located in a common cosmological structure, like a filament, is significantly reduced. Highly anisotropic outflows can travel across cosmological voids and deposit metals in other, unrelated cosmological structures.Comment: 32 pages, 9 figures (2 color). Revised version accepted in Ap

The Spatial Distribution of Metals in the Intergalactic Medium

We investigate the impact of environment on the metallicity of the diffuse intergalactic medium. We use pixel correlation techniques to search for weak CIV and OVI absorption in the spectrum of quasar Q1422+231 in regions of the spectrum close to and far from galaxies at z ~ 3. This is achieved both by using the positions of observed Lyman break galaxies and by using strong CIV absorption as a proxy for the presence of galaxies near the line of sight. We find that the metal line absorption is a strong function of not only the HI optical depth (and thus gas density) but also proximity to highly enriched regions (and so proximity to galaxies). The parameter ``proximity to galaxies'' can account for some, but not all, of the scatter in the strength of CIV absorption for fixed HI. Finally, we find that even if we limit our analysis to the two thirds of the pixels that are at least 600 km/s from any CIV line that is strong enough to detect unambiguously (tau_CIV > 0.1), our statistical analysis reveals only slightly less CIV for fixed HI than when we analyze the whole spectrum. We conclude that while the metallicity is enhanced in regions close to (Lyman-break) galaxies, the enrichment is likely to be much more widespread than their immediate surroundings.Comment: 16 pages, 7 figures. Accepted for publication in the Astrophysical Journal. Revised version taking referee's comments into account, minor change

A Strong Blend in the Morning: Studying the Circumgalactic Medium Before Cosmic Noon with Strong, Blended Lyman-α\alpha Forest Systems

We study of the properties of a new class of circumgalactic medium absorbers identified in the Lyman-$\alpha$ forest: "Strong, Blended Lyman-$\alpha$" (or SBLA) absorption systems. We study SBLAs at $2.4<z<3.1$ in SDSS-IV/eBOSS spectra by their strong extended Lyman-$\alpha$ absorption complexes covering 138 km/s with an integrated $\log (N_{HI}/$cm$^{-2}) =16.04^{+0.05}_{-0.06}$ and Doppler parameter $b=18.1^{+0.7}_{-0.4}$ km/s. Clustering with the Lyman-$\alpha$ forest provides a large-scale structure bias of $b = 2.34\pm0.06$ and halo mass estimate of $M_h \approx 10^{12}{\rm h^{-1}M_{sol}}$ for our SBLA sample. We measure the ensemble mean column densities of 22 metal features in the SBLA composite spectrum and find that no single-population multiphase model for them is viable. We therefore explore the underlying SBLA population by forward modelling the SBLA absorption distribution. Based on covariance measurements and favoured populations we find that $\approx 25$% of our SBLAs have stronger metals. Using silicon only we find that our strong metal SBLAs trace gas with a $\log(n_H /$cm$^{-3}) > -2.45$ for $T=10^{3.5}$K and show gas clumping on $<255$ parsec scales. We fit multiphase models to this strong sub-population and find a low ionization phase with $n_H=1$cm$^{-3}$, $T=10^{3.5}$K and $[X/H]=0.8$, an intermediate ionization phase with $\log(n_H /$cm$^{-3}) = -3.35$, $T=10^{3.5}$K and $[X/H]=-1.1$, and a poorly constrained higher ionization phase. We find that the low ionization phase traces cold, dense super-solar metallicity gas with a clumping scale of just 0.009 parsecs.Comment: 28 pages, submitted to MNRA

A Search for Oxygen in the Low-Density Lyman-alpha Forest Using the Sloan Digital Sky Survey

We use 2167 Sloan Digital Sky Survey (SDSS) quasar spectra to search for low-density oxygen in the Intergalactic Medium (IGM). Oxygen absorption is detected on a pixel-by-pixel basis by its correlation with Lyman-alpha forest absorption. We have developed a novel Locally Calibrated Pixel (LCP) search method that uses adjacent regions of the spectrum to calibrate interlopers and spectral artifacts, which would otherwise limit the measurement of OVI absorption. Despite the challenges presented by searching for weak OVI within the Lyman-alpha forest in spectra of moderate resolution and signal-to-noise, we find a highly significant detection of absorption by oxygen at 2.7 < z < 3.2 (the null hypothesis has a chi^2=80 for 9 data points). We interpret our results using synthetic spectra generated from a lognormal density field assuming a mixed quasar-galaxy photoionizing background (Haardt & Madau 2001) and that it dominates the ionization fraction of detected OVI. The LCP search data can be fit by a constant metallicity model with [O/H] = -2.15_(-0.09)^(+0.07), but also by models in which low-density regions are unenriched and higher density regions have a higher metallicity. The density-dependent enrichment model by Aguirre et al. (2008) is also an acceptable fit. All our successful models have similar mass-weighted oxygen abundance, corresponding to [_MW] = -2.45+-0.06. This result can be used to find the cosmic oxygen density in the Lyman-alpha forest, Omega_(Oxy, IGM) = 1.4(+-0.2)x10^(-6) = 3x10^(-4) Omega_b. This is the tightest constraint on the mass-weighted mean oxygen abundance and the cosmic oxygen density in the Lyman-alpha forest to date and indicates that it contains approximately 16% of metals produced by star formation (Bouch\'e et al. 2008) up to z = 3.Comment: 12 pages, 9 figures. Accepted by ApJ (minor changes

Probing the Circumgalactic Medium at High-Redshift Using Composite BOSS Spectra of Strong Lyman-alpha Forest Absorbers

We present composite spectra constructed from a sample of 242,150 Lyman-alpha (Lya) forest absorbers at redshifts 2.4<z<3.1 identified in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) as part of Data Release 9 of the Sloan Digital Sky Survey III. We select forest absorbers by their flux in bins 138 km/s wide (approximately the size of the BOSS resolution element). We split these absorbers into five samples spanning the range of flux -0.05 < F<0.45. Tests on a smaller sample of high-resolution spectra show that our three strongest absorption bins would probe circumgalactic regions (projected separation < 300 proper kpc and |Delta v| < 300km/s) in about 60% of cases for very high signal-to-noise ratio. Within this subset, weakening Lya absorption is associated with decreasing purity of circumgalactic selection once BOSS noise is included. Our weaker two Lya absorption samples are dominated by the intergalactic medium. We present composite spectra of these samples and a catalogue of measured absorption features from HI and 13 metal ionization species, all of which we make available to the community. We compare measurements of seven Lyman series transitions in our composite spectra to single line models and obtain further constraints from their associated excess Lyman limit opacity. This analysis provides results consistent with column densities over the range 14.4 <~ Log (N_HI) <~ 16.45. We compare our measurements of metal absorption to a variety of simple single-line, single-phase models for a preliminary interpretation. Our results imply clumping on scales down to ~30 pc and near-solar metallicities in the circumgalactic samples, while high-ionization metal absorption consistent with typical IGM densities and metallicities is visible in all samples.Comment: 23 pages, 15 figures, 5 tables, link to downloadable data included. Accepted by MNRAS 2014 March 20. New sections 3.4 and 6.1 limiting the occurrence and impact of Lyman limit system

Baryon Acoustic Oscillations in the Ly{\alpha} forest of BOSS DR11 quasars

We report a detection of the baryon acoustic oscillation (BAO) feature in the flux-correlation function of the Ly{\alpha} forest of high-redshift quasars with a statistical significance of five standard deviations. The study uses 137,562 quasars in the redshift range $2.1\le z \le 3.5$ 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, $D_A(z=2.34)$ and expansion rate, $H(z=2.34)$, both on a scale set by the sound horizon at the drag epoch, $r_d$. We find $D_A/r_d=11.28\pm0.65(1\sigma)^{+2.8}_{-1.2}(2\sigma)$ and $D_H/r_d=9.18\pm0.28(1\sigma)\pm0.6(2\sigma)$ where $D_H=c/H$. The optimal combination, $\sim D_H^{0.7}D_A^{0.3}/r_d$ is determined with a precision of $\sim2\%$. For the value $r_d=147.4~{\rm Mpc}$, consistent with the CMB power spectrum measured by Planck, we find $D_A(z=2.34)=1662\pm96(1\sigma)~{\rm Mpc}$ and $H(z=2.34)=222\pm7(1\sigma)~{\rm km\,s^{-1}Mpc^{-1}}$. Tests with mock catalogs and variations of our analysis procedure have revealed no systematic uncertainties comparable to our statistical errors. Our results agree with the previously reported BAO measurement at the same redshift using the quasar-Ly{\alpha} forest cross-correlation. The auto-correlation and cross-correlation approaches are complementary because of the quite different impact of redshift-space distortion on the two measurements. The combined constraints from the two correlation functions imply values of $D_A/r_d$ and $D_H/r_d$ that are, respectively, 7% low and 7% high compared to the predictions of a flat $\Lambda$CDM cosmological model with the best-fit Planck parameters. With our estimated statistical errors, the significance of this discrepancy is $\approx 2.5\sigma$.Comment: Accepted for publication in A&A. 17 pages, 18 figure

Mock Quasar-Lyman-{\alpha} Forest Data-sets for the SDSS-III Baryon Oscillation Spectroscopic Survey

We describe mock data-sets generated to simulate the high-redshift quasar sample in Data Release 11 (DR11) of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). The mock spectra contain Ly{\alpha} forest correlations useful for studying the 3D correlation function including Baryon Acoustic Oscillations (BAO). They also include astrophysical effects such as quasar continuum diversity and high-density absorbers, instrumental effects such as noise and spectral resolution, as well as imperfections introduced by the SDSS pipeline treatment of the raw data. The Ly{\alpha} forest BAO analysis of the BOSS collaboration, described in Delubac et al. 2014, has used these mock data-sets to develop and cross-check analysis procedures prior to performing the BAO analysis on real data, and for continued systematic cross checks. Tests presented here show that the simulations reproduce sufficiently well important characteristics of real spectra. These mock data-sets will be made available together with the data at the time of the Data Release 11.Comment: 35 pages, 19 figures, Accepted by JCA