27 research outputs found
A new measurement of the intergalactic temperature at z∼2.55 − 2.95
We present two measurements of the temperature-density relationship (TDR) of the intergalactic medium (IGM) in the redshift range 2.55 < z < 2.95 using a sample of 13 high-quality quasar spectra and high resolution numerical simulations of the IGM. Our approach is based on fitting the neutral hydrogen column density NHI and the Doppler parameter b of the absorption lines in the Lyα forest. The first measurement is obtained using a novel Bayesian scheme which takes into account the statistical correlations between the parameters characterising the lower cut-off of the b − NHI distribution and the power-law parameters T0 and γ describing the TDR. This approach yields T0/103 K = 15.6 ± 4.4 and γ = 1.45 ± 0.17 independent of the assumed pressure smoothing of the small scale density field. In order to explore the information contained in the overall b − NHI distribution rather than only the lower cut-off, we obtain a second measurement based on a similar Bayesian analysis of the median Doppler parameter for separate column-density ranges of the absorbers. In this case we obtain T0/103 K = 14.6 ± 3.7 and γ = 1.37 ± 0.17 in good agreement with the first measurement. Our Bayesian analysis reveals strong anti-correlations between the inferred T0 and γ for both methods as well as an anti-correlation of the inferred T0 and the pressure smoothing length for the second method, suggesting that the measurement accuracy can in the latter case be substantially increased if independent constraints on the smoothing are obtained. Our results are in good agreement with other recent measurements of the thermal state of the IGM probing similar (over-)density ranges
New limit on a varying proton-to-electron mass ratio from high resolution optical quasar spectra
Abstract not available
Radiative Decay of a Long-Lived Particle and Big-Bang Nucleosynthesis
The effects of radiatively decaying, long-lived particles on big-bang
nucleosynthesis (BBN) are discussed. If high-energy photons are emitted after
BBN, they may change the abundances of the light elements through
photodissociation processes, which may result in a significant discrepancy
between the BBN theory and observation. We calculate the abundances of the
light elements, including the effects of photodissociation induced by a
radiatively decaying particle, but neglecting the hadronic branching ratio.
Using these calculated abundances, we derive a constraint on such particles by
comparing our theoretical results with observations. Taking into account the
recent controversies regarding the observations of the light-element
abundances, we derive constraints for various combinations of the measurements.
We also discuss several models which predict such radiatively decaying
particles, and we derive constraints on such models.Comment: Published version in Phys. Rev. D. Typos in figure captions correcte
Assessing Big-Bang Nucleosynthesis
Systematic uncertainties in the light-element abundances and their evolution
make a rigorous statistical assessment difficult. However, using Bayesian
methods we show that the following statement is robust: the predicted and
measured abundances are consistent with 95\% credibility only if the
baryon-to-photon ratio is between and
and the number of light neutrino species is less than 3.9. Our analysis
suggests that the He abundance may have been systematically underestimated.Comment: 7 pages, LaTeX(2.09), 6 postscript figures (attached). A postscript
version with figures can be found at
ftp://astro.uchicago.edu/pub/astro/copi/assessing_BBN . (See the README file
for details
Non-Voigt Ly Absorption Line Profiles
Recent numerical simulations have lead to a paradigm shift in our
understanding of the intergalactic medium, and the loss of a physical
justification for Voigt profile fitting of the Lyman-alpha forest. Many
individual lines seen in simulated spectra have significant departures from the
Voigt profile, yet could be well fitted by a blend of two or more such lines.
We discuss the expected effect on the line profiles due to ongoing
gravitational structure formation and Hubble expansion. We develop a method to
detect departures from Voigt profiles of the absorption lines in a statistical
way and apply this method to simulated Lyman-alpha forest spectra, confirming
that the profiles seen do statistically differ from Voigt profiles.Comment: Accepted for publication in ApJL. 10 pages, 3 figure
High-redshift QSO absorbing clouds and the background ionizing source
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
H-alpha emission lines in high-redshift quasars
peer-reviewedInfrared spectra have been obtained of the H-alpha lines in 18 medium- to high-redshift QSOs and optical spectra taken nearly simultaneously to measure the strong UV line. It is found that the H-alpha line is redshifted by an average of 1000 km/s with respect to the lines from high ionization species such as C IV. Low ionization lines from ions like O I and Mg II are shifted by similar, or slightly smaller, amounts with respect to the high ionization lines. These results are difficult to reconcile with any simple models currently available, including those where dust obscuration is solely responsible for the observed velocity shifts. The similarity between the velocities of H-alpha and Mg II, O I provides some support for models in which the Balmer lines are produced predominantly in a warm H I region, while the Lyman lines arise mainly in a population of optically thin clouds. A velocity separation between the two cloud populations, along with some obscuration, could explain the main features
Temperature fluctuations in the intergalactic medium
The temperature of the low-density intergalactic medium is set by the balance
between adiabatic cooling resulting from the expansion of the universe, and
photo-heating by the UV-background. We have analysed the Lyman-alpha forest of
eleven high-resolution quasar spectra using wavelets, and find strong evidence
of a marked jump in the temperature at the mean density, T_0, of 60 per cent
around a redshift z=3.3, which we attribute to reionization of HeliumII. The
jump can be seen in all three of our spectra that straddle redshift 3.3, at a
significance of 99 per cent. Below z=3.1, our results are consistent with a
smooth cooling down of the universe, as expected when adiabatic expansion
dominates over photo-heating by a UV-background from QSOs and galaxies. We find
no evidence of thermal fluctuations on scales greater than 5000 km/s larger
than 50 per cent, which could be detected by our method, suggesting that the
IGM follows a reasonably well-defined temperature-density relation. We
demonstrate that the mean wavelet amplitude scales inversely with T_0 and
calibrate the relation with hydrodynamical simulations. We find T_0= 12000K at
z>3.6. Such high temperature suggest that Hydrogen reionization occured
relatively recent.Comment: 17 pages, minor changes, MNRAS published versio