1,282 research outputs found
Joint Bayesian Estimation of Quasar Continua and the Lyman-Alpha Forest Flux Probability Distribution Function
We present a new Bayesian algorithm making use of Markov Chain Monte Carlo
sampling that allows us to simultaneously estimate the unknown continuum level
of each quasar in an ensemble of high-resolution spectra, as well as their
common probability distribution function (PDF) for the transmitted Ly
forest flux. This fully automated PDF regulated continuum fitting method models
the unknown quasar continuum with a linear Principal Component Analysis (PCA)
basis, with the PCA coefficients treated as nuisance parameters. The method
allows one to estimate parameters governing the thermal state of the
intergalactic medium (IGM), such as the slope of the temperature-density
relation , while marginalizing out continuum uncertainties in a fully
Bayesian way. Using realistic mock quasar spectra created from a simplified
semi-numerical model of the IGM, we show that this method recovers the
underlying quasar continua to a precision of and at
and , respectively. Given the number of principal component spectra,
this is comparable to the underlying accuracy of the PCA model itself. Most
importantly, we show that we can achieve a nearly unbiased estimate of the
slope of the IGM temperature-density relation with a precision of
at , at , for an ensemble of ten mock
high-resolution quasar spectra. Applying this method to real quasar spectra and
comparing to a more realistic IGM model from hydrodynamical simulations would
enable precise measurements of the thermal and cosmological parameters
governing the IGM, albeit with somewhat larger uncertainties given the
increased flexibility of the model.Comment: 21 pages (+ Appendix), accepted at Ap
The Opacity of the Intergalactic Medium Measured Along Quasar Sightlines at
We publicly release a new sample of medium resolution quasar spectra at
observed with the Echellette Spectrograph and
Imager (ESI) on the Keck telescope. This quasar sample represents an ideal
laboratory to study the intergalactic medium (IGM) during the end stages of the
epoch of reionization, and constrain the timing and morphology of the phase
transition. For a subset of of our highest signal-to-noise ratio spectra
(S/N, per pixel), we present a new measurement of
the Lyman- (Ly) forest opacity spanning the redshift range
. We carefully eliminate spectral regions that could
be causing biases in our measurements due to additional transmitted flux in the
proximity zone of the quasars, or extra absorption caused by strong intervening
absorption systems along the line of sight. We compare the observed evolution
of the IGM opacity with redshift to predictions from a hydrodynamical
simulation with uniform ultraviolet background (UVB) radiation, as well as two
semi-numerical patchy reionization models, one with a fluctuating UVB and
another with a fluctuating temperature field. Our measurements show a steep
rise in opacity at and an increased scatter and thus support the
picture of a spatially inhomogeneous reionization process, consistent with
previous work. However, we measure significantly higher optical depths at
than previous studies, which reduces the contrast
between the highest opacity Gunn-Peterson troughs and the average opacity trend
of the IGM, which may relieve some of the previously noted tension between
these measurements and reionization models.Comment: accepted for publication at Ap
Fermi Surface of KFeAs from Quantum Oscillations in Magnetostriction
We present a study of the Fermi surface of KFeAs single crystals.
Quantum oscillations were observed in magnetostriction measured down to 50 mK
and in magnetic fields up to 14 T. For , the calculated
effective masses are in agreement with recent de Haas-van Alphen and ARPES
experiments, showing enhanced values with respect to the ones obtained from
previous band calculations. For , we observed a small orbit at a
cyclotron frequency of 64 T, characterized by an effective mass of , supporting the presence of a three-dimensional pocket at the Z-point.Comment: SCES Conference, Tokyo 201
An efficient grinder for ascospores and mycelium
An efficient grinder for ascospores and myceliu
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