183 research outputs found
Spitzer/IRS Imaging and Spectroscopy of the luminous infrared galaxy NGC 6052 (Mrk 297)
We present photometric and spectroscopic data of the interacting starburst
galaxy NGC 6052 obtained with the Spitzer Space Telescope. The mid-infrared
(MIR) spectra of the three brightest spatially resolved regions in the galaxy
are remarkably similar and are consistent with dust emission from young nearly
coeval stellar populations. Analysis of the brightest infrared region of the
system, which contributes ~18.5 % of the total 16\micron flux, indicates that
unlike similar off-nuclear infrared-bright regions found in Arp 299 or NGC
4038/9, its MIR spectrum is inconsistent with an enshrouded hot dust (T > 300K)
component. Instead, the three brightest MIR regions all display dust continua
of temperatures less than ~ 200K. These low dust temperatures indicate the dust
is likely in the form of a patchy screen of relatively cold material situated
along the line of sight. We also find that emission from polycyclic aromatic
hydrocarbons (PAHs) and the forbidden atomic lines is very similar for each
region. We conclude that the ionization regions are self-similar and come from
young (about 6 Myr) stellar populations. A fourth region, for which we have no
MIR spectra, exhibits MIR emission similar to tidal tail features in other
interacting galaxies.Comment: 20 pages in preprint form, estimated 7 pages in ApJ Aeptember 10,
2007, v666n 2 issue, six encapsulated postscript figure
ЭКОЛОГО-ЭПИЗООТОЛОГИЧЕСКИЕ ОСОБЕННОСТИ ЛЮМБРИЦИД – ПРОМЕЖУТОЧНЫХ ХОЗЯЕВ МЕТАСТРОНГИЛИД КАБАНА
The results of helminthological studying of hunting grounds for interactions in a complex of earthworms and larval stages of Metastrongylus sp. are given.Приведены результаты гельминтологического изучения охотничьих угодий на предмет взаимодействий в комплексе дождевых червей и личиночных стадий метастронгилид
Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XVI. A Thirteen-Year Study of Spectral Variability in NGC 5548
We present the final installment of an intensive 13-year study of variations
of the optical continuum and broad H-beta emission line in the Seyfert 1 galaxy
NGC 5548. The data base consists of 1530 optical continuum measurements and
1248 H-beta measurements. The H-beta variations follow the continuum variations
closely, with a typical time delay of about 20 days. However, a year-by-year
analysis shows that the magnitude of emission-line time delay is correlated
with the mean continuum flux. We argue that the data are consistent with the
simple model prediction that the size of the broad-line region is proportional
to the square root of the ionizing luminosity. Moreover, the apparently linear
nature of the correlation between the H-beta response time and the nonstellar
optical continuum arises as a consequence of the changing shape of the
continuum as it varies, specifically with the optical (5100 A) continuum
luminosity proportional to the ultraviolet (1350 A) continuum luminosity to the
0.56 power.Comment: 20 pages plus 4 figures. Accepted for publication in The
Astrophysical Journa
Quenching Factor for Low Energy Nuclear Recoils in a Plastic Scintillator
Plastic scintillators are widely used in industry, medicine and scientific
research, including nuclear and particle physics. Although one of their most
common applications is in neutron detection, experimental data on their
response to low-energy nuclear recoils are scarce. Here, the relative
scintillation efficiency for neutron-induced nuclear recoils in a
polystyrene-based plastic scintillator (UPS-923A) is presented, exploring
recoil energies between 125 keV and 850 keV. Monte Carlo simulations,
incorporating light collection efficiency and energy resolution effects, are
used to generate neutron scattering spectra which are matched to observed
distributions of scintillation signals to parameterise the energy-dependent
quenching factor. At energies above 300 keV the dependence is reasonably
described using the semi-empirical formulation of Birks and a kB factor of
(0.014+/-0.002) g/MeVcm^2 has been determined. Below that energy the measured
quenching factor falls more steeply than predicted by the Birks formalism.Comment: 8 pages, 9 figure
WIMP-nucleon cross-section results from the second science run of ZEPLIN-III
We report experimental upper limits on WIMP-nucleon elastic scattering cross
sections from the second science run of ZEPLIN-III at the Boulby Underground
Laboratory. A raw fiducial exposure of 1,344 kg.days was accrued over 319 days
of continuous operation between June 2010 and May 2011. A total of eight events
was observed in the signal acceptance region in the nuclear recoil energy range
7-29 keV, which is compatible with background expectations. This allows the
exclusion of the scalar cross-section above 4.8E-8 pb near 50 GeV/c^2 WIMP mass
with 90% confidence. Combined with data from the first run, this result
improves to 3.9E-8 pb. The corresponding WIMP-neutron spin-dependent
cross-section limit is 8.0E-3 pb. The ZEPLIN programme reaches thus its
conclusion at Boulby, having deployed and exploited successfully three liquid
xenon experiments of increasing reach
Single electron emission in two-phase xenon with application to the detection of coherent neutrino-nucleus scattering
We present an experimental study of single electron emission in ZEPLIN-III, a
two-phase xenon experiment built to search for dark matter WIMPs, and discuss
applications enabled by the excellent signal-to-noise ratio achieved in
detecting this signature. Firstly, we demonstrate a practical method for
precise measurement of the free electron lifetime in liquid xenon during normal
operation of these detectors. Then, using a realistic detector response model
and backgrounds, we assess the feasibility of deploying such an instrument for
measuring coherent neutrino-nucleus elastic scattering using the ionisation
channel in the few-electron regime. We conclude that it should be possible to
measure this elusive neutrino signature above an ionisation threshold of
3 electrons both at a stopped pion source and at a nuclear reactor.
Detectable signal rates are larger in the reactor case, but the triggered
measurement and harder recoil energy spectrum afforded by the accelerator
source enable lower overall background and fiducialisation of the active
volume
Electronic Transport in a Three-dimensional Network of 1-D Bismuth Quantum Wires
The resistance R of a high density network of 6 nm diameter Bi wires in
porous Vycor glass is studied in order to observe its expected semiconductor
behavior. R increases from 300 K down to 0.3 K. Below 4 K, where R varies
approximately as ln(1/T), the order-of-magnitude of the resistance rise, as
well as the behavior of the magnetoresistance are consistent with localization
and electron-electron interaction theories of a one-dimensional disordered
conductor in the presence of strong spin-orbit scattering. We show that this
behaviour and the surface-enhanced carrier density may mask the proposed
semimetal-to-semiconductor transition for quantum Bi wires.Comment: 19 pages total, 4 figures; accepted for publication in Phys. Rev.
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