14,771 research outputs found
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
On the residual Monge-Amp\`{e}re mass of plurisubharmonic functions with symmetry, II
The aim of this article is to study the residual Monge-Amp\`{e}re mass of a
plurisubharmonic function with an isolated singularity, provided with the
circular symmetry. With the aid of Sasakian geometry, we obtain an estimate on
the residual mass of this function with respect to its Lelong number and
maximal directional Lelong number. This result partially answers the zero mass
conjecture raised by Guedj and Rashkovskii.Comment: 35 page
A Parameter-free Statistical Measurement of Halos with Power Spectra
We show that, in the halo model of large-scale structure formation, the
difference between the Fourier and the DWT (discrete wavelet transform) power
spectra provides a statistical measurement of the halos. This statistical
quantity is free from parameters related to the shape of the mass profile and
the identification scheme of halos. That is, the statistical measurement is
invariant in the sense that models with reasonably defined and selected
parameters of the halo models should yield the same difference of the Fourier
and DWT spectra. This feature is useful to extract ensemble averaged properties
of halos, which cannot be obtained with the identification of individual halo.
To demonstrate this point, we show with WIGEON hydrodynamical simulation
samples that the spectrum difference provides a quantitative measurement of the
discrepancy of the distribution of baryonic gas from that of the underlying
dark matter field within halos. We also show that the mass density profile of
halos in physical space can be reconstructed with this statistical measurement.
This profile essentially is the average over an ensemble of halos, including
well virialized halos as well as halos with significant internal substructures.
Moreover, this reconstruction is sensitive to the tail of the mass density
profile. We showed that the profile with tail gives very different
result from that of . Other possible applications of this method are
discussed as well.Comment: To appear in ApJ, final versio
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