1,570 research outputs found
An entirely analytical cosmological model
The purpose of the present study is to show that in a particular cosmological
model, with an affine equation of state, one can obtain, besides the background
given by the scale factor, Hubble and deceleration parameters, a representation
in terms of scalar fields and, more important, explicit mathematical
expressions for the density contrast and the power spectrum. Although the model
so obtained is not realistic, it reproduces features observed in some previous
numerical studies and, therefore, it may be useful in the testing of numerical
codes and as a pedagogical tool.Comment: 4 pages (revtex4), 4 figure
Some integrals ocurring in a topology change problem
In a paper presented a few years ago, De Lorenci et al. showed, in the
context of canonical quantum cosmology, a model which allowed space topology
changes (Phys. Rev. D 56, 3329 (1997)). The purpose of this present work is to
go a step further in that model, by performing some calculations only estimated
there for several compact manifolds of constant negative curvature, such as the
Weeks and Thurston spaces and the icosahedral hyperbolic space (Best space).Comment: RevTeX article, 4 pages, 1 figur
TEMPERATURE AND RELATIVITY
We investigate whether inertial thermometers moving in a thermal bath behave
as being hotter or colder. This question is directly related to the classical
controversy concerning how temperature transforms under Lorentz
transformations. Rather than basing our arguments on thermodynamical
hypotheses, we perform straightforward calculations in the context of
relativistic quantum field theory. For this purpose we use Unruh-DeWitt
detectors, since they have been shown to be reliable thermometers in
semi-classical gravity. We believe that our discussion helps in definitely
clarifying this issue.Comment: 9 pages, 1 figure available upon reques
Background Thermal Contributions in Testing the Unruh Effect
We consider inertial and accelerated Unruh-DeWitt detectors moving in a
background thermal bath and calculate their excitation rates. It is shown that
for fast moving detectors such a thermal bath does not affect substantially the
excitation probability. Our results are discussed in connection with a possible
proposal of testing the Unruh effect in high energy particle accelerators.Comment: 13 pages, (REVTEX 3.0), 3 figures available upon reques
The first 62 AGN observed with SDSS-IV MaNGA - IV: gas excitation and star-formation rate distributions
We present maps of the ionized gas flux distributions, excitation,
star-formation rate SFR, surface mass density , and obtain total
values of SFR and ionized gas masses {\it M} for 62 Active Galactic Nuclei
(AGN) observed with SDSS-IV MaNGA and compare them with those of a control
sample of 112 non-active galaxies. The most luminous AGN -- with
L(\rm{[OIII]}\lambda 5007) \ge 3.8\times 10^{40}\,\mbox{erg}\,\mbox{s}^{-1},
and those hosted by earlier-type galaxies are dominated by Seyfert excitation
within 0.2 effective radius from the nucleus, surrounded by LINER
excitation or transition regions, while the less luminous and hosted by
later-type galaxies show equally frequent LINER and Seyfert excitation within
. The extent of the region ionized by the AGN follows the
relation -- as in the case of the Broad-Line
Region. The SFR distribution over the region ionized by hot stars is similar
for AGN and controls, while the integrated SFR -- in the range
\,M\,yr is also similar for the late-type
sub-sample, but higher in the AGN for 75\% of the early-type sub-sample. We
thus conclude that there is no signature of AGN quenching star formation in the
body of the galaxy in our sample. We also find that 66\% of the AGN have higher
ionized gas masses than the controls -- in the range
10\,M -- while 75\% of the AGN have higher
within than the control galaxies
The first 62 AGN observed with SDSS-IV MaNGA -- III: stellar and gas kinematics
We investigate the effects of Active Galactic Nuclei (AGN) on the gas
kinematics of their host galaxies, using MaNGA data for a sample of 62 AGN
hosts and 109 control galaxies (inactive galaxies). We compare orientation of
the line of nodes (kinematic Position Angle - PA) measured from the gas and
stellar velocity fields for the two samples. We found that AGN hosts and
control galaxies display similar kinematic PA offsets between gas and stars.
However, we note that AGN have larger fractional velocity dispersion
differences between gas and stars [] when compared to their controls, as
obtained from the velocity dispersion values of the central (nuclear) pixel
(2.5" diameter). The AGN have a median value of of
, while the the median value for the control
galaxies is . 75% of the AGN show
, while 75% of the normal galaxies show , thus we suggest that the parameter can be
used as an indicative of AGN activity. We find a correlation between the
[OIII]5007 luminosity and for our sample. Our main
conclusion is that the AGN already observed with MaNGA are not powerful enough
to produce important outflows at galactic scales, but at 1-2 kpc scales, AGN
feedback signatures are always present on their host galaxies.Comment: 19 pages, 8 figures, published in MNRA
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