2,756 research outputs found
Precision Cosmology from the Lyman-alpha Forest: Power Spectrum and Bispectrum
We investigate the promise of the Ly-alpha forest for high precision
cosmology in the era of the Sloan Digital Sky Survey using low order N-point
statistics. We show that with the existing data one can determine the
amplitude, slope and curvature of the slope of the matter power spectrum with a
few percent precision. Higher order statistics such as the bispectrum provide
independent information that can confirm and improve upon the statistical
precision from the power spectrum alone. The achievable precision is comparable
to that from the cosmic microwave background with upcoming satellites, and
complements it by measuring the power spectrum amplitude and shape at smaller
scales. Since the data cover the redshift range 2<z<4, one can also extract the
evolution of the growth factor and Hubble parameter over this range, and
provide useful constraints on the presence of dark energy at z>2.Comment: 14 pages, 17 figures, accepted to MNRAS; minor changes made (section
2) and references adde
Galaxies Inside Stromgren Spheres of Luminous Quasars at z>6: Detection of The First Galaxies
The intrinsic Lyman-alpha emission lines of normal galaxies before
reionization are much absorbed by the damping wing of the Gunn-Peterson trough,
rendering their direct detection nearly impossible, if their intrinsic line
widths are less than ~100km/s. High redshift luminous quasars prior to the
completion of cosmological reionization at z~6, on the other hand, are capable
of producing large HII regions around them (Stromgren spheres) to allow their
intrinsic Lyman-alpha emission lines to be transmitted without overwhelming
absorption (Cen & Haiman 2000). We suggest that targeted observations at the
Stromgren spheres of known luminous quasars at z >= 6 would be able to detect
Lyman-alpha emission lines of galaxies inside the Stromgren spheres largely
unattenuated. A tunable, very narrowband filter of \Delta\lambda\over \lambda ~
0.1% or a narrowband filter of \Delta\lambda\over \lambda ~1% with follow-up
spectroscopic identifications will be required. Such observations could
directly observe the sources of cosmological reionization including possibly
the Pop III galaxies at z=6-20 by JWST. Possible applications include
determinations of the ionization state of the intergalactic medium, the sizes
of the Stromgren spheres, the ages of the quasars, the luminosity function of
high redshift galaxies and its evolution, the spatial distribution of galaxies
and its evolution, the biased distribution of galaxies around quasars and the
anisotropy of quasar emission. Observations using Keck-class telescopes may
already be made to enable a differentiation between a fully neutral and a 10%
neutral intergalactic medium at z>6.Comment: Submitted to ApJ Letters, 10 page
Tracing the Warm Hot Intergalactic Medium in the local Universe
We present a simple method for tracing the spatial distribution and
predicting the physical properties of the Warm-Hot Intergalactic Medium (WHIM),
from the map of galaxy light in the local universe. Under the assumption that
biasing is local and monotonic we map the ~ 2 Mpc/h smoothed density field of
galaxy light into the mass density field from which we infer the spatial
distribution of the WHIM in the local supercluster. Taking into account the
scatter in the WHIM density-temperature and density-metallicity relation,
extracted from the z=0 outputs of high-resolution and large box size
hydro-dynamical cosmological simulations, we are able to quantify the
probability of detecting WHIM signatures in the form of absorption features in
the X-ray spectra, along arbitrary directions in the sky. To illustrate the
usefulness of this semi-analytical method we focus on the WHIM properties in
the Virgo Cluster region.Comment: 16 pages 11 Figures. Discussion clarified, alternative methods
proposed. Results unchanged. MNRAS in pres
X-ray Observations of the Warm-Hot Intergalactic Medium
We present Chandra observations that provide the most direct evidence to date
for the pervasive, moderate density, shock-heated intergalactic medium
predicted by leading cosmological scenarios. We also comment briefly on future
observations with Constellation-X.Comment: To be published in the proceedings of the conference "IGM/Galaxy
Connection- The Distribution of Baryons at z=0". 6 page
Cosmic Chemical Evolution
Numerical simulations of standard cosmological scenarios have now reached the
degree of sophistication required to provide tentative answers to the
fundamental question: Where and when were the heavy elements formed? Averaging
globally, these simulations give a metallicity that increases from 1% of the
solar value at to 20% at present. This conclusion is, in fact,
misleading, as it masks the very strong dependency of metallicity on local
density. At every epoch higher density regions have much higher metallicity
than lower density regions. Moreover, the highest density regions quickly
approach near solar metallicity and then saturate, while more typical regions
slowly catch up. These results are much more consistent with observational data
than the simpler picture (adopted by many) of gradual, quasi-uniform increase
of metallicity with time.Comment: ApJ(Letters) in press, 15 latex pages and 4 figure
Detecting X-ray filaments in the low redshift Universe with XEUS and Constellation-X
We propose a possible way to detect baryons at low redshifts from the
analysis of X-ray absorption spectra of bright AGN pairs. A simple
semi-analytical model to simulate the spectra is presented. We model the
diffuse warm-hot intergalactic medium (WHIM) component, responsible for the
X-ray absorption, using inputs from high-resolution hydro-dynamical simulations
and analytical prescriptions. We show that the number of OVII absorbers per
unit redshift with column density larger than cm -
corresponding to an equivalent width of 1 km/s - which will be possibly
detectable by {\it XEUS}, is \magcir 30 per unit redshift. {\it
Constellation-X} will detect OVII absorptions per unit redshift with
an equivalent width of 10 km/s. Our results show that, in a CDM
Universe, the characteristic size of these absorbers at is
Mpc. The filamentary structure of WHIM can be probed by finding
coincident absorption lines in the spectra of background AGN pairs. We estimate
that at least 20 AGN pairs at separation \mincir 20 arcmin are needed to
detect this filamentary structure at a 3 level. Assuming observations
of distant sources using {\it XEUS} for exposure times of 500 ksec, we find
that the minimum source flux to probe the filamentary structure is erg cm s, in the 0.1-2.4 keV energy band. Thus,
most pairs of these extragalactic X-ray bright sources have already been
identified in the {\it ROSAT} All-Sky Survey. Re-observation of these objects
by future missions could be a powerful way to search for baryons in the low
redshift Universe.Comment: 18 pages, 10 Figures. Two figures added, Sections 2 and 3 expanded.
More optimistic results for Constellation-X. Accepted by MNRA
An X-ray WHIM metal absorber from a Mpc-scale empty region of space
We report a detection of an absorption line at ~44.8 {\AA} in a > 500 ks
Chandra HRC-S/LETG X-ray grating spectrum of the blazar H 2356-309. This line
can be identified as intervening CV-K{\alpha} absorption, at z\approx0.112,
produced by a warm (log T = 5.1 K) intergalactic absorber. The feature is
significant at a 2.9{\sigma} level (accounting for the number of independent
redshift trials). We estimate an equivalent hydrogen column density of log
N_H=19.05 (Z/Zsun)^-1 cm^-2. Unlike other previously reported FUV/X-ray metal
detections of warm-hot intergalactic medium (WHIM), this CV absorber lies in a
region with locally low galaxy density, at ~2.2 Mpc from the closest galaxy at
that redshift, and therefore is unlikely to be associated with an extended
galactic halo. We instead tentatively identify this absorber with an
intervening Warm-Hot Intergalactic Medium filament possibly permeating a
large-scale, 30 Mpc extended, structure of galaxies whose redshift centroid,
within a cylinder of 7.5 Mpc radius centered on the line of sight to H
2356-309, is marginally consistent (at a 1.8{\sigma} level) with the redshift
of the absorber.Comment: ApJ accepted, 6 pages, 3 figure
XMM-Newton discovery of O VII emission from warm gas in clusters of galaxies
XMM-Newton recently discovered O VII line emission from ~2 million K gas near
the outer parts of several clusters of galaxies. This emission is attributed to
the Warm-Hot Intergalactic Medium. The original sample of clusters studied for
this purpose has been extended and two more clusters with a soft X-ray excess
have been found. We discuss the physical properties of the warm gas, in
particular the density, spatial extent, abundances and temperature.Comment: 8 pages, 3 figures, conference "Soft X-ray emission from clusters of
galaxies and related phenomena", ed. R. Lieu, Kluwer, in pres
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