20 research outputs found
On the Normalization of the QSO's Lyman alpha Forest Power Spectrum
The calculation of the transmission power spectrum of QSO's Lyman alpha
absorption requires two parameters for the normalization: the continuum Fc and
mean transmission, i.e. average of e^{-tau}. Traditionally, the continuum is
obtained by a polynomial fitting truncating it at a lower order, and the mean
transmission is calculated over the entire wavelength range considered. The
flux F is then normalized by the average of Fc e^{-tau}. However, the
fluctuations in the transmitted flux are significantly correlated with the
local background flux on scales for which the field is intermittent. In this
paper, we develop a self-normalization algorithm of the transmission power
spectrum based on a multiresolution analysis. This self-normalized power
spectrum estimator needs neither a continuum fitting, nor pre-determining the
mean transmission. With simulated samples, we show that the self-normalization
algorithm can perfectly recover the transmission power spectrum from the flux
regardless of how the continuum varies with wavelength. We also show that the
self-normalized power spectrum is also properly normalized by the mean
transmission. Moreover, this power spectrum estimator is sensitive to the
non-linear behavior of the field. That is, the self-normalized power spectrum
estimator can distinguish between fields with or without the
fluctuation-background correlation. This cannot be accomplished by the power
spectrum with the normalization by an overall mean transmission. Therefore, the
self-normalized power spectrum would be useful for the discrimination among
models without the uncertainties caused by free (or fitting) parameters.Comment: 24 pages, 8 figures, to appear in ApJ tentatively in the Nov 1 2001
issu
Ly Leaks in the Absorption Spectra of High Redshift QSOs
Spectra of high redshift QSOs show deep Gunn-Peterson absorptions on the blue
sides of the \Lya emissions lines. They can be decomposed into components
called \Lya leaks, defined to be emissive regions in complementary to otherwise
zero-fluxed absorption gaps. Just like \Lya absorption forests at low
redshifts, \Lya leaks are both easy to find in observations and containing rich
sets of statistical properties that can be used to study the early evolution of
the IGM. Among all properties of a leak profile, we investigate its equivalent
width in this paper, since it is weakly affected by instrumental resolution and
noise. Using 10 Keck QSO spectra at , we have measured the number
density distribution function , defined to be the number of leaks per
equivalent width and per redshift , in the redshift range .
These new observational statistics, in both the differential and cumulative
forms, fit well to hydro numerical simulations of uniform ionizing background
in the CDM cosmology. In this model, Ly leaks are mainly due
to low density voids. It supports the early studies that the IGM at
would still be in a highly ionized state with neutral hydrogen fraction . Measurements of at would be effective to probe the
reionization of the IGM.Comment: 3 figs, accepted by ApJ
Abundance and Clustering of C IV Absorption Systems in the SCDM, LCDM and CHDM Models
We have developed a method for calculating the two-point correlation function
of nonlinearly evolved mass and collapsed halos in the Press-Schechter
formalism. The nonlinear gravitational interaction is treated as the sum of
various individual spherical top-hat clustering. Because no collapsed halo of
mass M can exist in initial regions (or top-hat spheres) of mass less than M,
the bias that massive halos have stronger correlation than the background mass
can be naturally introduced. We apply this method to derive constraints on
popular dark-matter models from the spatial number density and the correlation
function of C IV absorption systems in QSO spectra. Considering C IV systems
should behosted by collapsed halos, one can obtain an upper limit to the
threshold mass of the collapsed halos by requiring their number density to be
larger than that of observed C IV systems. On the other hand, in order to
explain the observed clustering of C IV systems, a lower limit to the threshold
mass will be set for the hosting halos. The cold dark matter model, the Lamda
CDM model and the cold-plus-hot dark matter model are tested using the C IV
observations.Comment: 23 pages, LaTeX, plus 11 figures in the PS format to be published in
Ap
Is the cosmic UV background fluctuating at redshift z ~ 6 ?
We study the Gunn-Peterson effect of the photo-ionized intergalactic
medium(IGM) in the redshift range 5< z <6.4 using semi-analytic simulations
based on the lognormal model. Assuming a rapidly evolved and spatially uniform
ionizing background, the simulation can produce all the observed abnormal
statistical features near redshift z ~ 6. They include: 1) rapidly increase of
absorption depths; 2) large scatter in the optical depths; 3) long-tailed
distributions of transmitted flux and 4) long dark gaps in spectra. These
abnormal features are mainly due to rare events, which correspond to the
long-tailed probability distribution of the IGM density field, and therefore,
they may not imply significantly spatial fluctuations in the UV ionizing
background at z ~ 6.Comment: 12 pages, 4 figs, accepted by ApJ
Ly Leaks and Reionization
Ly absorption spectra of QSOs at redshifts show complete
Gunn-Peterson absorption troughs (dark gaps) separated by tiny leaks. The dark
gaps are from the intergalactic medium (IGM) where the density of neutral
hydrogen are high enough to produce almost saturated absorptions, however,
where the transmitted leaks come from is still unclear so far. We demonstrate
that leaking can originate from the lowest density voids in the IGM as well as
the ionized patches around ionizing sources using semi-analytical simulations.
If leaks were produced in lowest density voids, the IGM might already be highly
ionized, and the ionizing background should be almost uniform; in contrast, if
leaks come from ionized patches, the neutral fraction of IGM would be still
high, and the ionizing background is significantly inhomogeneous. Therefore,
the origin of leaking is crucial to determining the epoch of
inhomogeneous-to-uniform transition of the the ionizing photon background. We
show that the origin could be studied with the statistical features of leaks.
Actually, Ly leaks can be well defined and described by the equivalent
width and the full width of half area , both of which are less
contaminated by instrumental resolution and noise. It is found that the
distribution of and of Ly leaks are sensitive to the
modeling of the ionizing background. We consider four representative
reionization models. It is concluded that the leak statistics provides an
effective tool to probe the evolutionary history of reionization at
. Similar statistics would also be applicable to the reionization
of He II at (Abridged)Comment: 11 pages including 10 figures, accepted for publication in MNRA
Hydrogen Clouds before Reionization: a Lognormal Model Approach
We study the baryonic gas clouds (the IGM) in the universe before the
reionization with the lognormal model which is shown to be dynamcially
legitimate in describing the fluctuation evolution in quasilinear as well as
nonlinear regimes in recent years. The probability distribution function of the
mass field in the LN model is long tailed and so plays an important role in
rare events, such as the formation of the first generation of baryonic objects.
We calculate density and velocity distributions of the IGM at very high spatial
resolutions, and simulate the distributions at resolution of 0.15 kpc from z=7
to 15 in the LCDM cosmological model. We performed a statistics of the hydrogen
clouds including column densities, clumping factors, sizes, masses, and spatial
number density etc. One of our goals is to identify which hydrogen clouds are
going to collapse. By inspecting the mass density profile and the velocity
profile of clouds, we found that the velocity outflow significantly postpones
the collapsing process in less massive clouds, in spite of their masses are
larger than the Jeans mass. Consequently, only massive (> 10^5 M_sun) clouds
can form objects at higher redshift, and less massive (10^4-10^5) collapsed
objects are formed later. For example, although the mass fraction in clouds
with sizes larger than the Jeans length is already larger than 1 at z=15, there
is only a tiny fraction of mass (10^{-8}) in the clouds which are collapsed at
that time. If all the ionizing photons, and the 10^{-2} metallicity observed at
low redshift are produced by the first 1% mass of collapsed baryonic clouds,
the majority of those first generation objects would not happen until z=10.Comment: Paper in AAStex, 12 figure
Application of carbon nanoparticles combined with refined extracapsular anatomy in endoscopic thyroidectomy
ObjectiveTo evaluate the value of refined extracapsular anatomy combined with carbon nanoparticle suspension tracing technology for protecting parathyroid function and the thoroughness of lymph node dissection in the central region during endoscopic thyroid cancer surgery.Patients and methodsRetrospective clinical data analysis was performed on 108 patients who underwent endoscopic thyroid cancer surgery at the First Affiliated Hospital of Wannan Medical College (Yijishan Hospital) from November 2019 to November 2022. Before surgery, thyroid function tests, color Doppler ultrasounds and neck-enhanced CT scans were performed on all patients. Cytopathological diagnosis obtained via ultrasound-guided fine-needle aspiration served as confirmation for the primary diagnosis. It was determined whether to perform a total thyroidectomy or a hemithyroidectomy (HT) together with preventive unilateral (ipsilateral) central neck dissection. Follow-up times were 1 to 34 months.ResultsTransient neuromuscular symptoms were present in 3.70% (4/108) cases, with no permanent neuromuscular symptoms or permanent hypoparathyroidism. Regarding transient hypoparathyroidism, the patients recovered after three months and did not need long-term calcium supplementation. The number of harvested LNs (mean± SD) was 5.54 ± 3.84, with â€5 in 57.41% (62/108) and >5 in 42.59% (46/108) cases. The number of patients with metastatic LNs was 37.96% (41/108), with â€2 in 65.85% (27/41) and >2 in 34.15% (14/41) cases.ConclusionsFine extracapsular anatomy combined with carbon nanoparticle suspension tracing is effective in endoscopic thyroid cancer surgery. It can improve the thoroughness of prophylactic central neck dissection and recognition of the parathyroid gland and avoid parathyroid injury and other complications to effectively protect parathyroid function