3,276 research outputs found
Supernova Explosions in the Early Universe: Evolution of Radiative Remnants and the Halo Destruction Efficiency
We study the evolution of supernova (SN) remnants of the first stars, taking
proper account of the radiative feedback of the progenitor stars on the
surroundings. We carry out a series of one-dimensional hydrodynamic simulations
with radiative cooling, starting from initial configurations that are drawn
from the results of our earlier radiation hydrodynamic simulations of the first
HII regions. In low-mass (< 10^6 M_sun) halos, the stellar radiation
significantly reduces the ambient gas density prior to the SN explosion. The
blastwave quickly propagates over the halo's virial radius, leading to complete
evacuation of the gas even with the input energy of 10^50 erg. We find that a
large fraction of the remnant's thermal energy is lost in 0.1-10 Myr by line
cooling, whereas, for larger explosion energies, the remnant expands even more
rapidly with decreasing interior density, and cools predominantly via inverse
Compton process. In higher mass halos, the gas density near the explosion site
remains high and the SN shock is heavily confined; the thermal energy of the
remnant is quickly radiated away by free-free emission, even if the total input
energy exceeds the binding energy of halos by two orders of magnitude. We show
that the efficiency of halo destruction is determined not only by the explosion
energy but also by the gas density profile, and thus controlled by radiative
feedback prior to the explosion. Several implications of our results for the
formation of first quasars and second-generation stars in the universe are also
discussed.Comment: 13 pages, 11 embedded figures. Accepted for publication in Ap
START: Smoothed particle hydrodynamics with tree-based accelerated radiative transfer
We present a novel radiation hydrodynamics code, START, which is a smoothed
particle hydrodynamics (SPH) scheme coupled with accelerated radiative
transfer. The basic idea for the acceleration of radiative transfer is parallel
to the tree algorithm that is hitherto used to speed up the gravitational force
calculation in an N-body system. It is demonstrated that the radiative transfer
calculations can be dramatically accelerated, where the computational time is
scaled as Np log Ns for Np SPH particles and Ns radiation sources. Such
acceleration allows us to readily include not only numerous sources but also
scattering photons, even if the total number of radiation sources is comparable
to that of SPH particles. Here, a test simulation is presented for a multiple
source problem, where the results with START are compared to those with a
radiation SPH code without tree-based acceleration. We find that the results
agree well with each other if we set the tolerance parameter as < 1.0, and then
it demonstrates that START can solve radiative transfer faster without reducing
the accuracy. One of important applications with START is to solve the transfer
of diffuse ionizing photons, where each SPH particle is regarded as an emitter.
To illustrate the competence of START, we simulate the shadowing effect by
dense clumps around an ionizing source. As a result, it is found that the
erosion of shadows by diffuse recombination photons can be solved. Such an
effect is of great significance to reveal the cosmic reionization process.Comment: 14 pages, 23 figures, accepted for publication in MNRA
Constraints on Primordial Nongaussiantiy from the High-Redshift Cluster MS1054--03
The implications of the massive, X-ray selected cluster of galaxies
MS1054--03 at are discussed in light of the hypothesis that the
primordial density fluctuations may be nongaussian. We generalize the
Press-Schechter (PS) formalism to the nongaussian case, and calculate the
likelihood that a cluster as massive as MS1054 would appear in the EMSS. The
probability of finding an MS1054-like cluster depends only on \omegam and the
extent of primordial nongaussianity. We quantify the latter by adopting a
specific functional form for the PDF, denoted which tends to
Gaussianity for and show how is related to the more
familiar statistic the probability of fluctuations for a
given PDF relative to a Gaussian. We find that Gaussian initial density
fluctuations are consistent with the data on MS1054 only if \omegam\simlt
0.2. For \omegam\ge 0.25 a significant degree of nongaussianity is required,
unless the mass of MS1054 has been substantially overestimated by X-ray and
weak lensing data. The required amount of nongaussianity is a rapidly
increasing function of \omegam for 0.25 \le \omegam \le 0.45, with (T \simgt 7) at the upper end of this range. For a fiducial
\omegam=0.3, \omegal=0.7 universe, favored by several lines of evidence we
obtain an upper limit corresponding to a This
finding is consistent with the conclusions of Koyama, Soda, & Taruya (1999),
who applied the generalized PS formalism to low (z\simlt 0.1) and
intermediate (z\simlt 0.6) redshift cluster data sets.Comment: 15 pages, 11 figures, submitted to the Astrophysical Journal, uses
emulateapj.st
Chandra View of the Dynamically Young Cluster of Galaxies A1367 I. Small-Scale Structures
The 40 ks \emph{Chandra} ACIS-S observation of A1367 provides new insights
into small-scale structures and point sources in this dynamically young
cluster. Here we concentrate on small-scale extended structures. A ridge-like
structure around the center (``the ridge'') is significant in the \chandra\
image. The ridge, with a projected length of 8 arcmin (or 300
h kpc), is elongated from northwest (NW) to southeast (SE), as is
the X-ray surface brightness distribution on much larger scales ( 2
h Mpc). The ridge is cooler than its western and southern
surroundings while the differences from its eastern and northern surroundings
are small. We also searched for small-scale structures with sizes
arcmin. Nine extended features, with sizes from 0.5 to 1.5, were
detected at significance levels above 4 . Five of the nine features are
located in the ridge and form local crests. The nine extended features can be
divided into two types. Those associated with galaxies (NGC 3860B, NGC 3860 and
UGC 6697) are significantly cooler than their surroundings (0.3 - 0.9 keV vs. 3
- 4.5 keV). The masses of their host galaxies are sufficient to bind the
extended gas. These extended features are probably related to thermal halos or
galactic superwinds of their host galaxies. The existence of these relatively
cold halos imply that galaxy coronae can survive in cluster environment (e.g.,
Vikhlinin et al. 2001). Features of the second type are not apparently
associated with galaxies. Their temperatures may not be significantly different
from those of their surroundings. This class of extended features may be
related to the ridge. We consider several possibilities for the ridge and the
second type of extended features. The merging scenario is preferred.Comment: To appear in ApJ, Vol 576, 2002, Sep., a high-resolution version is
in http://cfa160.harvard.edu/~sunm/a1367_a.ps.g
Synthesis, Structure, and Ferromagnetism of a New Oxygen Defect Pyrochlore System Lu2V2O_{7-x} (x = 0.40-0.65)
A new fcc oxygen defect pyrochlore structure system Lu2V2O_{7-x} with x =
0.40 to 0.65 was synthesized from the known fcc ferromagnetic semiconductor
pyrochlore compound Lu2V2O7 which can be written as Lu2V2O6O' with two
inequivalent oxygen sites O and O'. Rietveld x-ray diffraction refinements
showed significant Lu-V antisite disorder for x >= 0.5. The lattice parameter
versus x (including x = 0) shows a distinct maximum at x ~ 0.4. We propose that
these observations can be explained if the oxygen defects are on the O'
sublattice of the structure. The magnetic susceptibility versus temperature
exhibits Curie-Weiss behavior above 150 K for all x, with a Curie constant C
that increases with x as expected in an ionic model. However, the magnetization
measurements also show that the (ferromagnetic) Weiss temperature theta and the
ferromagnetic ordering temperature T_C both strongly decrease with increasing x
instead of increasing as expected from C(x). The T_C decreases from 73 K for x
= 0 to 21 K for x = 0.65. Furthermore, the saturation moment at a field of 5.5
T at 5 K is nearly independent of x, with the value expected for a fixed spin
1/2 per V. The latter three observations suggest that Lu2V2O_{7-x} may contain
localized spin 1/2 vanadium moments in a metallic background that is induced by
oxygen defect doping, instead of being a semiconductor as suggested by the C(x)
dependence.Comment: 9 pages including 7 figures, 3 table
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