8,011 research outputs found
A Hubble Space Telescope Survey of Extended [OIII]5007A Emission in a Far-Infrared Selected Sample of Seyfert Galaxies: Results
We present the results of a Hubble Space Telescope (HST) survey of extended
[OIII] emission in a sample of 60 nearby Seyfert galaxies (22 Seyfert 1's and
38 Seyfert 2's), selected by mostly isotropic properties. The comparison
between the semi major axis size of their [OIII] emitting regions (R_Maj) shows
that Seyfert 1's and Seyfert 2's have similar distributions, which seems to
contradict Unified Model predictions. We discuss possible ways to explain this
result, which could be due either to observational limitations or the models
used for the comparison with our data. We show that Seyfert 1 Narrow Line
Regions (NLR's) are more circular and concentrated than Seyfert 2's, which can
be attributed to foreshortening in the former. We find a good correlation
between the NLR size and luminosity, following the relation R_Maj propto
L([OIII])^0.33, which is flatter than a previous one found for QSO's and
Seyfert 2's. We discuss possible reasons for the different results, and their
implications to photoionization models. We confirm previous results which show
that the [OIII] and radio emission are well aligned, and also find no
correlation between the orientation of the extended [OIII] emission and the
host galaxy major axis. This agrees with results showing that the torus axis
and radio jet are not aligned with the host galaxy rotation axis, indicating
that the orientation of the gas in the torus, and not the spin of the black
hole, determine the orientation of the accretion disk, and consequently the
orientation of the radio jet.Comment: 17 pages including 12 figures, to appear in Ap
Effects of heavy modes on vacuum stability in supersymmetric theories
We study the effects induced by heavy fields on the masses of light fields in
supersymmetric theories, under the assumption that the heavy mass scale is much
higher than the supersymmetry breaking scale. We show that the square-masses of
light scalar fields can get two different types of significant corrections when
a heavy multiplet is integrated out. The first is an indirect level-repulsion
effect, which may arise from heavy chiral multiplets and is always negative.
The second is a direct coupling contribution, which may arise from heavy vector
multiplets and can have any sign. We then apply these results to the sGoldstino
mass and study the implications for the vacuum metastability condition. We find
that the correction from heavy chiral multiplets is always negative and tends
to compromise vacuum metastability, whereas the contribution from heavy vector
multiplets is always positive and tends on the contrary to reinforce it. These
two effects are controlled respectively by Yukawa couplings and gauge charges,
which mix one heavy and two light fields respectively in the superpotential and
the Kahler potential. Finally we also comment on similar effects induced in
soft scalar masses when the heavy multiplets couple both to the visible and the
hidden sector.Comment: LaTex, 24 pages, no figures; v2 some comments and references adde
Turbulence in the Solar Atmosphere: Manifestations and Diagnostics via Solar Image Processing
Intermittent magnetohydrodynamical turbulence is most likely at work in the
magnetized solar atmosphere. As a result, an array of scaling and multi-scaling
image-processing techniques can be used to measure the expected
self-organization of solar magnetic fields. While these techniques advance our
understanding of the physical system at work, it is unclear whether they can be
used to predict solar eruptions, thus obtaining a practical significance for
space weather. We address part of this problem by focusing on solar active
regions and by investigating the usefulness of scaling and multi-scaling
image-processing techniques in solar flare prediction. Since solar flares
exhibit spatial and temporal intermittency, we suggest that they are the
products of instabilities subject to a critical threshold in a turbulent
magnetic configuration. The identification of this threshold in scaling and
multi-scaling spectra would then contribute meaningfully to the prediction of
solar flares. We find that the fractal dimension of solar magnetic fields and
their multi-fractal spectrum of generalized correlation dimensions do not have
significant predictive ability. The respective multi-fractal structure
functions and their inertial-range scaling exponents, however, probably provide
some statistical distinguishing features between flaring and non-flaring active
regions. More importantly, the temporal evolution of the above scaling
exponents in flaring active regions probably shows a distinct behavior starting
a few hours prior to a flare and therefore this temporal behavior may be
practically useful in flare prediction. The results of this study need to be
validated by more comprehensive works over a large number of solar active
regions.Comment: 26 pages, 7 figure
Observed Effect of Magnetic Fields on the Propagation of Magnetoacoustic Waves in the Lower Solar Atmosphere
We study Hinode/SOT-FG observations of intensity fluctuations in Ca II H-line
and G-band image sequences and their relation to simultaneous and co-spatial
magnetic field measurements. We explore the G-band and H-line intensity
oscillation spectra both separately and comparatively via their relative phase
differences, time delays and cross-coherences. In the non-magnetic situations,
both sets of fluctuations show strong oscillatory power in the 3 - 7 mHz band
centered at 4.5 mHz, but this is suppressed as magnetic field increases. A
relative phase analysis gives a time delay of H-line after G-band of 20\pm1 s
in non-magnetic situations implying a mean effective height difference of 140
km. The maximum coherence is at 4 - 7 mHz. Under strong magnetic influence the
measured delay time shrinks to 11 s with the peak coherence near 4 mHz. A
second coherence maximum appears between 7.5 - 10 mHz. Investigation of the
locations of this doubled-frequency coherence locates it in diffuse rings
outside photospheric magnetic structures. Some possible interpretations of
these results are offered.Comment: 19 pages, 6 figure
The Frequency of Active and Quiescent Galaxies with Companions: Implications for the Feeding of the Nucleus
We analyze the idea that nuclear activity, either AGN or star formation, can
be triggered by interactions, studying the percentage of active, HII and
quiescent galaxies with companions. Our sample was selected from the Palomar
survey, and avoids selection biases faced by previous studies. The comparison
between the local galaxy density distributions showed that in most cases there
is no statistically significant difference among galaxies of different activity
types. The comparison of the percentage of galaxies with nearby companions
showed that there is a higher percentage of LINERs, transition, and absorption
line galaxies with companions than Seyferts and HII galaxies. However, we find
that when we consider only galaxies of similar morphological types (ellipticals
or spirals), there is no difference in the percentage of galaxies with
companions among different activity types, indicating that the former result
was due to the morphology-density effect. Also, only small differences are
found when we consider galaxies with similar Halpha luminosities. The
comparison between HII galaxies of different Halpha luminosities shows that
there is a significantly higher percentage of galaxies with companions among
the higher luminosity HII galaxies, indicating that interactions increase the
amount of circumnuclear star formation, in agreement with previous results. The
fact that we find that galaxies of different activity types have the same
percentage of companions, suggests that interactions between galaxies is not a
necessary condition to trigger the nuclear activity in AGNs. We compare our
results with previous ones and discuss their implications. (abridged)Comment: 30 pages, including 6 figures and 3 tables. To appear in The
Astronomical Journal, November issu
Library of medium-resolution fiber optic echelle spectra of F, G, K, and M field dwarfs to giants stars
We present a library of Penn State Fiber Optic Echelle (FOE) observations of
a sample of field stars with spectral types F to M and luminosity classes V to
I. The spectral coverage is from 3800 AA to 10000 AA with nominal a resolving
power 12000. These spectra include many of the spectral lines most widely used
as optical and near-infrared indicators of chromospheric activity such as the
Balmer lines (H_alpha, H_beta), Ca II H & K, Mg I b triplet, Na I D_{1} and
D_{2}, He I D_{3}, and Ca II IRT lines. There are also a large number of
photospheric lines, which can also be affected by chromospheric activity, and
temperature sensitive photospheric features such as TiO bands. The spectra have
been compiled with the goal of providing a set of standards observed at medium
resolution. We have extensively used such data for the study of active
chromosphere stars by applying a spectral subtraction technique. However, the
data set presented here can also be utilized in a wide variety of ways ranging
from radial velocity templates to study of variable stars and stellar
population synthesis. This library can also be used for spectral classification
purposes and determination of atmospheric parameters (T_eff, log{g}, [Fe/H]). A
digital version of all the fully reduced spectra is available via ftp and the
World Wide Web (WWW) in FITS format.Comment: Latex file with 17 pages, 4 figures. Full postscript (text and
figures) available at http://www.ucm.es/info/Astrof/fgkmsl/FOEfgkmsl.html To
be published in ApJ
Applicability of layered sine-Gordon models to layered superconductors: II. The case of magnetic coupling
In this paper, we propose a quantum field theoretical renormalization group
approach to the vortex dynamics of magnetically coupled layered
superconductors, to supplement our earlier investigations on the
Josephson-coupled case. We construct a two-dimensional multi-layer sine-Gordon
type model which we map onto a gas of topological excitations. With a special
choice of the mass matrix for our field theoretical model, vortex dominated
properties of magnetically coupled layered superconductors can be described.
The well known interaction potentials of fractional flux vortices are
consistently obtained from our field-theoretical analysis, and the physical
parameters (vortex fugacity and temperature parameter) are also identified. We
analyse the phase structure of the multi-layer sine--Gordon model by a
differential renormalization group method for the magnetically coupled case
from first principles. The dependence of the transition temperature on the
number of layers is found to be in agreement with known results based on other
methods.Comment: 7 pages, 1 figure, published in J. Phys.: Condens. Matte
Stellar Populations in the Host Galaxies of Mrk 1014, IRAS 07598+6508, and Mrk 231
We present deep spectroscopic and imaging data of the host galaxies of Mrk
1014, IRAS 07598+6508, and Mrk 231. These objects form part of both the QSO and
the ultraluminous infrared galaxy (ULIG) families, and may represent a
transition stage in an evolutionary scenario. Our imaging shows that all three
objects have highly perturbed hosts with tidal tails and destroyed disks, and
appear to be in the final stages of major mergers. The host galaxies of the
three objects have spectra typical of E+A galaxies, showing simultaneously
features from an old and a young stellar component. We model spectra from
different regions of the host galaxies using Bruzual & Charlot spectral
synthesis models using two component models including an old underlying
population and recent superposed starbursts. Our results indicate a strong
connection between interactions and vigorous bursts of star formation in these
objects. We propose that the starburst ages found are indicative of young ages
for the QSO activity. The young starburst ages found are also consistent with
the intermediate position of these objects in the far infrared color-color
diagram. (abridged)Comment: 28 pages; uses AASTeX 5.02 and includes 6 eps figures. 9 additional
figures in jpeg format. Postscript version including all 15 figures (6264 kb)
available at http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
the October issue of A
Tumor site immune markers associated with risk for subsequent basal cell carcinomas.
BackgroundBasal cell carcinoma (BCC) tumors are the most common skin cancer and are highly immunogenic.ObjectiveThe goal of this study was to assess how immune-cell related gene expression in an initial BCC tumor biopsy was related to the appearance of subsequent BCC tumors.Materials and methodsLevels of mRNA for CD3ε (a T-cell receptor marker), CD25 (the alpha chain of the interleukin (IL)-2 receptor expressed on activated T-cells and B-cells), CD68 (a marker for monocytes/macrophages), the cell surface glycoprotein intercellular adhesion molecule-1 (ICAM-1), the cytokine interferon-γ (IFN-γ) and the anti-inflammatory cytokine IL-10 were measured in BCC tumor biopsies from 138 patients using real-time PCR.ResultsThe median follow-up was 26.6 months, and 61% of subjects were free of new BCCs two years post-initial biopsy. Patients with low CD3ε CD25, CD68, and ICAM-1 mRNA levels had significantly shorter times before new tumors were detected (p = 0.03, p = 0.02, p = 0.003, and p = 0.08, respectively). Furthermore, older age diminished the association of mRNA levels with the appearance of subsequent tumors.ConclusionsOur results show that levels of CD3ε, CD25, CD68, and ICAM-1 mRNA in BCC biopsies may predict risk for new BCC tumors
Gravitation: Global Formulation and Quantum Effects
A nonintegrable phase-factor global approach to gravitation is developed by
using the similarity of teleparallel gravity with electromagnetism. The phase
shifts of both the COW and the gravitational Aharonov-Bohm effects are
obtained. It is then shown, by considering a simple slit experiment, that in
the classical limit the global approach yields the same result as the
gravitational Lorentz force equation of teleparallel gravity. It represents,
therefore, the quantum mechanical version of the classical description provided
by the gravitational Lorentz force equation. As teleparallel gravity can be
formulated independently of the equivalence principle, it will consequently
require no generalization of this principle at the quantum level.Comment: Latex (IOP style), 14 pages, 3 figures. To appear in Classical and
Quantum Gravit
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