21,040 research outputs found
NoSOCS in SDSS. VI. The Environmental Dependence of AGN in Clusters and Field in the Local Universe
We investigated the variation in the fraction of optical active galactic
nuclei (AGN) hosts with stellar mass, as well as their local and global
environments. Our sample is composed of cluster members and field galaxies at
and we consider only strong AGN. We find a strong variation in the
AGN fraction () with stellar mass. The field population comprises a
higher AGN fraction compared to the global cluster population, especially for
objects with log . Hence, we restricted our analysis to more
massive objects. We detected a smooth variation in the with local
stellar mass density for cluster objects, reaching a plateau in the field
environment. As a function of clustercentric distance we verify that
is roughly constant for R R, but show a steep decline inwards. We
have also verified the dependence of the AGN population on cluster velocity
dispersion, finding a constant behavior for low mass systems ( km s). However, there is a strong decline in
for higher mass clusters ( 700 km s). When comparing the in
clusters with or without substructure we only find different results for
objects at large radii (R R), in the sense that clusters with
substructure present some excess in the AGN fraction. Finally, we have found
that the phase-space distribution of AGN cluster members is significantly
different than other populations. Due to the environmental dependence of
and their phase-space distribution we interpret AGN to be the result
of galaxy interactions, favored in environments where the relative velocities
are low, typical of the field, low mass groups or cluster outskirts.Comment: 11 pages, 10 figures, Accepted to MNRA
Nonlinear gyrofluid computation of edge localised ideal ballooning modes
Three dimensional electromagnetic gyrofluid simulations of the ideal
ballooning mode blowout scenario for tokamak edge localized modes (ELMs) are
presented. Special emphasis is placed on energetic diagnosis, examining changes
in the growth rate in the linear, overshoot, and decay phases. The saturation
process is energy transfer to self generated edge turbulence which exhibits an
ion temperature gradient (ITG) mode structure. Convergence in the decay phase
is found only if the spectrum reaches the ion gyroradius. The equilibrium is a
self consistent background whose evolution is taken into account. Approximately
two thirds of the total energy in the edge layer is liberated in the blowout.
Parameter dependence with respect to plasma pressure and the ion gyroradius is
studied. Despite the violent nature of the short-lived process, the transition
to nonlinearity is very similar to that found in generic tokamak edge
turbulence.Comment: The following article has been submitted to Physics of Plasmas. After
it is published, it will be found at http://pop.aip.org
Dogmatism and Theoretical Pluralism in Modern Cosmology
This work discusses the presence of a dogmatic tendency within modern
cosmology, and some ideas capable of neutralizing its negative influence. It is
verified that warnings about the dangers of dogmatic thinking in cosmology can
be found as early as the 1930's, and we discuss the modern appearance of
"scientific dogmatism". The solution proposed to counteract such an influence,
which is capable of neutralizing this dogmatic tendency, has its origins in the
philosophical thinking of the Austrian physicist Ludwig Boltzmann (1844-1906).
In particular we use his two main epistemological theses, scientific theories
as representations of nature and theoretical pluralism, to show that once they
are embodied in the research practice of modern cosmology, there is no longer
any reason for dogmatic behaviours.Comment: 14 pages; LaTeX sourc
Boltzmann's Concept of Reality
In this article we describe and analyze the concept of reality developed by
the Austrian theoretical physicist Ludwig Boltzmann. It is our thesis that
Boltzmann was fully aware that reality could, and actually was, described by
different points of view. In spite of this, Boltzmann did not renounce the idea
that reality is real. We also discuss his main motivations to be strongly
involved with philosophy of science, as well as further developments made by
Boltzmann himself of his main philosophical ideas, namely scientific theories
as images of Nature and its consequences. We end the paper with a discussion
about the modernity of Boltzmann's philosophy of science.Comment: 13 pages, pdf only. To appear in the book on Ludwig Boltzmann
scientific philosophy, published by Nova Science. Edited by A. Eftekhar
Fractal analysis of the galaxy distribution in the redshift range 0.45 < z < 5.0
Evidence is presented that the galaxy distribution can be described as a
fractal system in the redshift range of the FDF galaxy survey. The fractal
dimension was derived using the FDF galaxy volume number densities in the
spatially homogeneous standard cosmological model with ,
and H_0=70 \; \mbox{km} \; {\mbox{s}}^{-1} \;
{\mbox{Mpc}}^{-1}. The ratio between the differential and integral number
densities and obtained from the red and blue FDF
galaxies provides a direct method to estimate , implying that and
vary as power-laws with the cosmological distances. The
luminosity distance , galaxy area distance
and redshift distance were plotted against
their respective number densities to calculate by linear fitting. It was
found that the FDF galaxy distribution is characterized by two single fractal
dimensions at successive distance ranges. Two straight lines were fitted to the
data, whose slopes change at or depending on
the chosen cosmological distance. The average fractal dimension calculated
using changes from to for all galaxies, and decreases as
increases. Small values of at high mean that in the past galaxies were
distributed much more sparsely and the large-scale galaxy structure was then
possibly dominated by voids. Results of Iribarrem et al. (2014,
arXiv:1401.6572) indicating similar fractal features with in the far-infrared sources of the Herschel/PACS evolutionary
probe (PEP) at are also mentioned.Comment: LaTex, 15 pages, 28 figures, 4 tables. To appear in "Physica A
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