2,109 research outputs found
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- Forest Systems
We study of the properties of a new class of circumgalactic medium absorbers
identified in the Lyman- forest: "Strong, Blended Lyman-" (or
SBLA) absorption systems. We study SBLAs at in SDSS-IV/eBOSS
spectra by their strong extended Lyman- absorption complexes covering
138 km/s with an integrated cm
and Doppler parameter km/s.
Clustering with the Lyman- forest provides a large-scale structure
bias of and halo mass estimate of 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 % of our SBLAs have stronger metals. Using silicon only we
find that our strong metal SBLAs trace gas with a cm for K and show gas clumping on parsec scales. We fit
multiphase models to this strong sub-population and find a low ionization phase
with cm, K and , an intermediate
ionization phase with cm, K and
, 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 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,
and expansion rate, , both on a scale set by the sound
horizon at the drag epoch, . We find
and
where . The optimal
combination, is determined with a precision of
. For the value , consistent with the CMB power
spectrum measured by Planck, we find
and . 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 and
that are, respectively, 7% low and 7% high compared to the
predictions of a flat CDM cosmological model with the best-fit Planck
parameters. With our estimated statistical errors, the significance of this
discrepancy is .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
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