6,188 research outputs found
Imbedding estimates and elliptic equations with discontinuous coefficients in unbounded domains
In this paper we deal with the multiplication operator u ∈ W^{k,p} (Ω) → gu ∈ L^q (Ω), with g belonging to a space of Morrey type. We apply our results in order to establish an a-priori bound for the solutions of the Dirichlet problem concerning elliptic equations with discontinuous coefficients
Sunyaev-Zel'dovich Effects from Quasars in Galaxies and Groups
The energy fed by active galactic nuclei to the surrounding diffuse baryons
changes their amount, temperature, and distribution; so in groups and in member
galaxies it affects the X-ray luminosity and also the Sunyaev-Zel'dovich
effect. Here we compute how the latter is enhanced by the transient blastwave
driven by an active quasar, and is depressed when the equilibrium is recovered
with a depleted density. We constrain such depressions and enhancements with
the masses of relic black holes in galaxies and the X-ray luminosities in
groups. We discuss how all these linked observables can tell the quasar
contribution to the thermal history of the baryons pervading galaxies and
groups.Comment: 4 pages, 3 figures, uses REVTeX4 and emulateapj.cls. Accepted by ApJ
Extracting Galaxy Cluster Gas Inhomogeneity from X-ray Surface Brightness: A Statistical Approach and Application to Abell 3667
Our previous analysis indicates that small-scale fluctuations in the
intracluster medium (ICM) from cosmological hydrodynamic simulations follow the
lognormal distribution. In order to test the lognormal nature of the ICM
directly against X-ray observations of galaxy clusters, we develop a method of
extracting statistical information about the three-dimensional properties of
the fluctuations from the two-dimensional X-ray surface brightness.
We first create a set of synthetic clusters with lognormal fluctuations.
Performing mock observations of these synthetic clusters, we find that the
resulting X-ray surface brightness fluctuations also follow the lognormal
distribution fairly well. Systematic analysis of the synthetic clusters
provides an empirical relation between the density fluctuations and the X-ray
surface brightness. We analyze \chandra observations of the galaxy cluster
Abell 3667, and find that its X-ray surface brightness fluctuations follow the
lognormal distribution. While the lognormal model was originally motivated by
cosmological hydrodynamic simulations, this is the first observational
confirmation of the lognormal signature in a real cluster. Finally we check the
synthetic cluster results against clusters from cosmological hydrodynamic
simulations. As a result of the complex structure exhibited by simulated
clusters, the empirical relation shows large scatter. Nevertheless we are able
to reproduce the true value of the fluctuation amplitude of simulated clusters
within a factor of two from their X-ray surface brightness alone.
Our current methodology combined with existing observational data is useful
in describing and inferring the statistical properties of the three dimensional
inhomogeneity in galaxy clusters.Comment: 34 pages, 17 figures, accepted for publication in Ap
The U-band Galaxy Luminosity Function of Nearby Clusters
Despite the great potential of the U-band galaxy luminosity function (GLF) to
constrain the history of star formation in clusters, to clarify the question of
variations of the GLF across filter bands, to provide a baseline for
comparisons to high-redshift studies of the cluster GLF, and to estimate the
contribution of bound systems of galaxies to the extragalactic near-UV
background, determinations have so far been hampered by the generally low
efficiency of detectors in the U-band and by the difficulty of constructing
both deep and wide surveys. In this paper, we present U-band GLFs of three
nearby, rich clusters to a limit of M_U=-17.5 (M*_U+2). Our analysis is based
on a combination of separate spectroscopic and R-band and U-band photometric
surveys. For this purpose, we have developed a new maximum-likelihood algorithm
for calculating the luminosity function that is particularly useful for
reconstructing the galaxy distribution function in multi-dimensional spaces
(e.g., the number of galaxies as a simultaneous function of luminosity in
different filter bands, surface brightness, star formation rate, morphology,
etc.), because it requires no prior assumptions as to the shape of the
distribution function.
The composite luminosity function can be described by a Schechter function
with characteristic magnitude M*_U=-19.82+/-0.27 and faint end slope
alpha_U=-1.09+/-0.18. The total U-band GLF is slightly steeper than the R-band
GLF, indicating that cluster galaxies are bluer at fainter magnitudes.
Quiescent galaxies dominate the cumulative U-band flux for M_U<-14. The
contribution of galaxies in nearby clusters to the U-band extragalactic
background is <1% Gyr^-1 for clusters of masses ~3*10^14 to 2*10^15 M_solar.Comment: 44 pages, 11 figures, accepted for publication in Ap
Evidence of diffusive fractal aggregation of TiO2 nanoparticles by femtosecond laser ablation at ambient conditions
The specific mechanisms which leads to the formation of fractal
nanostructures by pulsed laser deposition remain elusive despite intense
research efforts, motivated mainly by the technological interest in obtaining
tailored nanostructures with simple and scalable production methods. Here we
focus on fractal nanostructures of titanium dioxide, , a strategic
material for many applications, obtained by femtosecond laser ablation at
ambient conditions. We model the fractal formation through extensive Monte
Carlo simulations based on a set of minimal assumptions: irreversible sticking
and size independent diffusion. Our model is able to reproduce the fractal
dimensions and the area distributions of the nanostructures obtained in the
experiments for different densities of the ablated material. The comparison of
theory and experiment show that such fractal aggregates are formed after
landing of the ablated material on the substrate surface by a diffusive
mechanism. Finally we discuss the role of the thermal conductivity of the
substrate and the laser fluence on the properties of the fractal
nanostructures. Our results represent an advancement towards controlling the
production of fractal nanostructures by pulsed laser deposition.Comment: 21 page
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