9,070 research outputs found
The subarcsecond mid-infrared view of local active galactic nuclei: III. Polar dust emission
Recent mid-infrared (MIR) interferometric observations showed in few active
galactic nuclei (AGN) that the bulk of the infrared emission originates from
the polar region above the putative torus, where only little dust should be
present. Here, we investigate whether such strong polar dust emission is common
in AGN. Out of 149 Seyferts in the MIR atlas of local AGN (Asmus et al.), 21
show extended MIR emission on single dish images. In 18 objects, the extended
MIR emission aligns with the system axis position angle, established by [OIII],
radio, polarisation and maser based position angle measurements. The relative
amount of resolved MIR emission is at least 40 per cent and scales with the
[OIV] fluxes implying a strong connection between the extended continuum and
[OIV] emitters. These results together with the radio-quiet nature of the
Seyferts support the scenario that the bulk of MIR emission is emitted by dust
in the polar region and not by the torus, which would demand a new paradigm for
the infrared emission structure in AGN. The current low detection rate of polar
dust in the AGN of the MIR atlas is explained by the lack of sufficient high
quality MIR data and the requirement for the orientation, NLR strength and
distance of the AGN. The James-Webb Space Telescope will enable much deeper
nuclear MIR studies with comparable angular resolution, allowing us to resolve
the polar emission and surroundings in most of the nearby AGN.Comment: Accepted for publication in ApJ on Mar 08 (submitted Dec 22
Energy Shaping Control of an Inverted Flexible Pendulum Fixed to a Cart
Control of compliant mechanical systems is increasingly being researched for
several applications including flexible link robots and ultra-precision
positioning systems. The control problem in these systems is challenging,
especially with gravity coupling and large deformations, because of inherent
underactuation and the combination of lumped and distributed parameters of a
nonlinear system. In this paper we consider an ultra-flexible inverted pendulum
on a cart and propose a new nonlinear energy shaping controller to keep the
pendulum at the upward position with the cart stopped at a desired location.
The design is based on a model, obtained via the constrained Lagrange
formulation, which previously has been validated experimentally. The controller
design consists of a partial feedback linearization step followed by a standard
PID controller acting on two passive outputs. Boundedness of all signals and
(local) asymptotic stability of the desired equilibrium is theoretically
established. Simulations and experimental evidence assess the performance of
the proposed controller.Comment: 11 pages, 7 figures, extended version of the NOLCOS 2016 pape
VLT near-infrared spectra of hard serendipitous Chandra sources
We present near-infrared long-slit spectra of eight optically-dim X-ray
sources obtained with ISAAC on the Very Large Telescope. Six of the sources
have hard X-ray emission with a significant fraction of the counts emerging
above 2 keV. All were discovered serendipitously in the fields of three nearby
galaxy clusters observed with Chandra, and identified through near-infrared
imaging. The X-ray fluxes lie close to the break in the source counts. Two of
the sources show narrow emission lines, and a third has a broad line. One of
the narrow line-emitting sources has a clear redshift identification at z=2.18,
while the other has a tentative determination based on the highest redshift
detection of He I 10830 at z=1.26. The remainder have featureless spectra to
deep limiting equivalent widths of 20--60 angstroms and line flux approx= 5 x
10^{-17} erg/s/cm^2 in the K-band. High-quality J, H and Ks--band images of the
sources were combined with archival optical detections or limits to estimate a
photometric redshift for six. Two sources show complex double morphology. The
hard sources have spectral count ratios consistent with heavily obscured AGN,
while the host galaxy emits much of the optical and near-infrared flux. The
most likely explanation for the featureless continua is that the line photons
are being scattered or destroyed by optically-thick gas and associated dust
with large covering fractions.Comment: Replaced in response to problems with the PDF version of Fig 4 at
arxiv.org, but not at the mirror sites (lanl.gov, soton.ac.uk). No content
change
Resolving the Mass Hierarchy with Atmospheric Neutrinos using a Liquid Argon Detector
We explore the potential offered by large-mass Liquid Argon detectors for
determination of the sign of Delta m_{31}^2, or the neutrino mass hierarchy,
through interactions of atmospheric neutrinos. We give results for a 100 kT
sized magnetized detector which provides separate sensitivity to \nu_\mu,
\bar{\nu}_\mu and, over a limited energy range, to \nu_e, \bar{\nu}_e.We also
discuss the sensitivity for the unmagnetized version of such a detector. After
including the effect of smearing in neutrino energy and direction and
incorporating the relevant statistical,theoretical and systematic errors, we
perform a binned \chi^2 analysis of simulated data. The \chi^2 is marginalized
over the presently allowed ranges of neutrino parameters and determined as a
function of \theta_{13}. We find that such a detector offers superior
capabilities for hierarchy resolution, allowing a > 4\sigma determination for a
100 kT detector over a 10 year running period for values of \sin^2 2\theta_{13}
\ge 0.05. For an unmagnetized detector, a 2.5\sigma hierarchy sensitivity is
possible for \sin^2 2\theta_{13} = 0.04.Comment: 13 pages, 3 figures, typing error in the abstract corrected, no other
chang
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