15,721 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
Temperature effect on (2+1) experimental Kardar-Parisi-Zhang growth
We report on the effect of substrate temperature (T) on both local structure
and long-wavelength fluctuations of polycrystalline CdTe thin films deposited
on Si(001). A strong T-dependent mound evolution is observed and explained in
terms of the energy barrier to inter-grain diffusion at grain boundaries, as
corroborated by Monte Carlo simulations. This leads to transitions from
uncorrelated growth to a crossover from random-to-correlated growth and
transient anomalous scaling as T increases. Due to these finite-time effects,
we were not able to determine the universality class of the system through the
critical exponents. Nevertheless, we demonstrate that this can be circumvented
by analyzing height, roughness and maximal height distributions, which allow us
to prove that CdTe grows asymptotically according to the Kardar-Parisi-Zhang
(KPZ) equation in a broad range of T. More important, one finds positive
(negative) velocity excess in the growth at low (high) T, indicating that it is
possible to control the KPZ non-linearity by adjusting the temperature.Comment: 6 pages, 5 figure
Magnetocaloric effect in integrable spin-s chains
We study the magnetocaloric effect for the integrable antiferromagnetic
high-spin chain. We present an exact computation of the Gr\"uneisen parameter,
which is closely related to the magnetocaloric effect, for the quantum spin-s
chain on the thermodynamical limit by means of Bethe ansatz techniques and the
quantum transfer matrix approach. We have also calculated the entropy S and the
isentropes in the (H,T) plane. We have been able to identify the quantum
critical points H_c^{(s)}=2/(s+1/2) looking at the isentropes and/or the
characteristic behaviour of the Gr\"uneisen parameter.Comment: 6 pages, 3 figure
Aharonov-Bohm signature for neutral excitons in type-II quantum dot ensembles
It is commonly believed that the Aharonov-Bohm (AB) effect is a typical
feature of the motion of a charged particle interacting with the
electromagnetic vector potential. Here we present a magnetophotoluminescence
study of type-II InP/GaAs self-assembled quantum dots, unambiguously revealing
the Aharonov-Bohm-type oscillations for neutral excitons when the hole ground
state changes its angular momentum from lh = 0 to lh = 1, 2, and 3. The hole
ring parameters derived from a simple model are in excellent agreement with the
structural parameters for this system.Comment: Revised version, 10 pages, 3 figure
Non-Gaussian velocity distributions - The effect on virial mass estimates of galaxy groups
We present a study of 9 galaxy groups with evidence for non-Gaussianity in
their velocity distributions out to 4R200. This sample is taken from 57 groups
selected from the 2PIGG catalog of galaxy groups. Statistical analysis
indicates that non-Gaussian groups have masses significantly higher than
Gaussian groups. We also have found that all non-Gaussian systems seem to be
composed of multiple velocity modes. Besides, our results indicate that
multimodal groups should be considered as a set of individual units with their
own properties. In particular, we have found that the mass distribution of such
units are similar to that of Gaussian groups. Our results reinforce the idea of
non-Gaussian systems as complex structures in the phase space, likely
corresponding to secondary infall aggregations at a stage before virialization.
The understanding of these objects is relevant for cosmological studies using
groups and clusters through the mass function evolution.Comment: 5 pages, 4 figures and 2 tables. Accepted for publication in the
MNRA
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