184 research outputs found
Lyman-alpha forest-CMB cross-correlation and the search for the ionized baryons at high redshift
The intergalactic neutral hydrogen which is responsible for the Lyman alpha
forest of quasar absorption is a tracer of much larger amounts of ionised
hydrogen. The ionised component has yet to be detected directly, but is
expected to scatter CMB photons via the Sunyaev-Zel'dovich (SZ) effect. We use
hydrodynamic simulations of a LambdaCDM universe to create mock quasar spectra
and CMB sky maps. We find that the high-z Lya forest gas causes temperature
fluctuations of the order of 1 muK rms in the CMB on arcmin scales. The kinetic
and thermal SZ effects have a similar magnitude at z=3, with the thermal effect
becoming relatively weaker as expected at higher z. The CMB signal associated
with lines of sight having HI column densities > 10^18 cm^-2 is only marginally
stronger than that for lower column densities. The strong dependence of rms
temperature fluctuation on mean Lya absorbed flux, however, suggests that the
CMB signal effectively arises in lower density material. We investigate the use
of the cross-correlation of the Lya forest and the microwave background to
detect the SZ effect at redshifts 2-4. In so doing we are able to set direct
limits on the density of diffuse ionised intergalactic baryons. We carry out a
preliminary comparison at a mean redshift z=3 of 3488 quasar spectra from SDSS
Data Release 3 and the WMAP first year data. Assuming that the baryons are
clustered as in a LambdaCDM cosmology, and have the same mean temperature, the
cross-correlation yields a weak limit on the cosmic density of ionised baryons
Omega_(b,I), which is Omega_(b,I) < 0.8 at 95% confidence. With data from
upcoming CMB telescopes, we anticipate that a direct detection of the high
redshift ionised IGM will soon be possible, providing an important consistency
check on cosmological models.Comment: 14 pages, 10 figures, submitted to MNRA
Weak lensing of the Lyman-alpha forest
The angular positions of quasars are deflected by the gravitational lensing
effect of foreground matter. The Lyman-alpha forest seen in the spectra of
these quasars is therefore also lensed. We propose that the signature of weak
gravitational lensing of the forest could be measured using similar techniques
that have been applied to the lensed Cosmic Microwave Background, and which
have also been proposed for application to spectral data from 21cm radio
telescopes. As with 21cm data, the forest has the advantage of spectral
information, potentially yielding many lensed "slices" at different redshifts.
We perform an illustrative idealized test, generating a high resolution angular
grid of quasars (of order arcminute separation), and lensing the
Lyman-alphaforest spectra at redshifts z=2-3 using a foreground density field.
We find that standard quadratic estimators can be used to reconstruct images of
the foreground mass distribution at z~1. There currently exists a wealth of Lya
forest data from quasar and galaxy spectral surveys, with smaller sightline
separations expected in the future. Lyman-alpha forest lensing is sensitive to
the foreground mass distribution at redshifts intermediate between CMB lensing
and galaxy shear, and avoids the difficulties of shape measurement associated
with the latter. With further refinement and application of mass reconstruction
techniques, weak gravitational lensing of the high redshift Lya forest may
become a useful new cosmological probe.Comment: 9 pages, 7 figures, submitted to MNRA
Noise Estimates for Measurements of Weak Lensing from the Lyman-alpha Forest
We have proposed a method for measuring weak lensing using the Lyman-alpha
forest. Here we estimate the noise expected in weak lensing maps and power
spectra for different sets of observational parameters. We find that surveys of
the size and quality of the ones being done today and ones planned for the
future will be able to measure the lensing power spectrum at a source redshift
of z~2.5 with high precision and even be able to image the distribution of
foreground matter with high fidelity on degree scales. For example, we predict
that Lyman-alpha forest lensing measurement from the Dark Energy Spectroscopic
Instrument survey should yield the mass fluctuation amplitude with statistical
errors of 1.5%. By dividing the redshift range into multiple bins some
tomographic lensing information should be accessible as well. This would allow
for cosmological lensing measurements at higher redshift than are accessible
with galaxy shear surveys and correspondingly better constraints on the
evolution of dark energy at relatively early times.Comment: 8 pages, 8 figures, submitted to MNRA
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