5,480 research outputs found
LIINUS/SERPIL: a design study for interferometric imaging spectroscopy at the LBT
LIINUS/SERPIL is a design study to augment LBTs interferometric beam combiner
camera LINC-NIRVANA with imaging spectroscopy. The FWHM of the interferometric
main beam at 1.5 micron will be about 10 mas, offering unique imaging and
spectroscopic capabilities well beyond the angular resolution of current 8-10m
telescopes. At 10 mas angular scale, e.g., one resolution element at the
distance of the Galactic Center corresponds to the average diameter of the
Pluto orbit (79 AU), hence the size of the solar system. Taking advantage of
the LBT interferometric beam with an equivalent maximum diameter of 23 m,
LIINUS/SERPIL is an ideal precursor instrument for (imaging) spectrographs at
extremely large full aperture telescopes. LIINUS/SERPIL will be built upon the
LINC-NIRVANA hardware and LIINUS/SERPIL could potentially be developed on a
rather short timescale. The study investigates several concepts for the optical
as well as for the mechanical design. We present the scientific promises of
such an instrument together with the current status of the design study.Comment: 12 pages, SPIE conference proceeding, Orlando, 200
The central molecular gas structure in LINERs with low luminosity AGN: evidence for gradual disappearance of the torus
We present observations of the molecular gas in the nuclear environment of
three prototypical low luminosity AGN (LLAGN), based on VLT/SINFONI AO-assisted
integral-field spectroscopy of H2 1-0 S(1) emission at angular resolutions of
~0.17". On scales of 50-150 pc the spatial distribution and kinematics of the
molecular gas are consistent with a rotating thin disk, where the ratio of
rotation (V) to dispersion (sigma) exceeds unity. However, in the central 50
pc, the observations reveal a geometrically and optically thick structure of
molecular gas (V/sigma10^{23} cm^{-2}) that is likely to be
associated with the outer extent of any smaller scale obscuring structure. In
contrast to Seyfert galaxies, the molecular gas in LLAGN has a V/sigma<1 over
an area that is ~9 times smaller and column densities that are in average ~3
times smaller. We interpret these results as evidence for a gradual
disappearance of the nuclear obscuring structure. While a disk wind may not be
able to maintain a thick rotating structure at these luminosities, inflow of
material into the nuclear region could provide sufficient energy to sustain it.
In this context, LLAGN may represent the final phase of accretion in current
theories of torus evolution. While the inflow rate is considerable during the
Seyfert phase, it is slowly decreasing, and the collisional disk is gradually
transitioning to become geometrically thin. Furthermore, the nuclear region of
these LLAGN is dominated by intermediate-age/old stellar populations (with
little or no on-going star formation), consistent with a late stage of
evolution.Comment: 15 pages, including 4 figures and 1 table, Accepted for publication
in ApJ Letter
The Keck/OSIRIS Nearby AGN Survey (KONA) I. The Nuclear K-band Properties of Nearby AGN
We introduce the Keck Osiris Nearby AGN survey (KONA), a new adaptive
optics-assisted integral-field spectroscopic survey of Seyfert galaxies. KONA
permits at ~0.1" resolution a detailed study of the nuclear kinematic structure
of gas and stars in a representative sample of 40 local bona fide active
galactic nucleus (AGN). KONA seeks to characterize the physical processes
responsible for the coevolution of supermassive black holes and galaxies,
principally inflows and outflows. With these IFU data of the nuclear regions of
40 Seyfert galaxies, the KONA survey will be able to study, for the first time,
a number of key topics with meaningful statistics. In this paper we study the
nuclear K-band properties of nearby AGN. We find that the luminosities of the
unresolved Seyfert 1 sources at 2.1 microns are correlated with the hard X-ray
luminosities, implying that the majority of the emission is non-stellar. The
best-fit correlation is logLK = 0.9logL2-10 keV + 4 over 3 orders of magnitude
in both K-band and X-ray luminosities. We find no strong correlation between
2.1 microns luminosity and hard X-ray luminosity for the Seyfert 2 galaxies.
The spatial extent and spectral slope of the Seyfert 2 galaxies indicate the
presence of nuclear star formation and attenuating material (gas and dust),
which in some cases is compact and in some galaxies extended. We detect
coronal-line emission in 36 galaxies and for the first time in five galaxies.
Finally, we find 4/20 galaxies that are optically classified as Seyfert 2 show
broad emission lines in the near-IR, and one galaxy (NGC 7465) shows evidence
of a double nucleus.Comment: Accepted for publication in ApJ, 19 pages with 18 figure
Emitters of -photon bundles
We propose a scheme based on the coherent excitation of a two-level system in
a cavity to generate an ultrabright CW and focused source of quantum light that
comes in groups (bundles) of photons, for an integer tunable with the
frequency of the exciting laser. We define a new quantity, the \emph{purity} of
-photon emission, to describe the percentage of photons emitted in bundles,
thus bypassing the limitations of Glauber correlation functions. We focus on
the case and show that close to 100% of two-photon emission and
90% of three-photon emission is within reach of state of the art cavity QED
samples. The statistics of the bundles emission shows that various
regimes---from -photon lasing to -photon guns---can be realized. This is
evidenced through generalized correlation functions that extend the standard
definitions to the multi-photon level.Comment: Introduce the n-th order N-photon correlation functions. Reorganized
to emphasize the N-photon emitter, now extended to the antibunching regime,
rather than only coherent emission as previsoul
Optimization of soliton ratchets in inhomogeneous sine-Gordon systems
Unidirectional motion of solitons can take place, although the applied force
has zero average in time, when the spatial symmetry is broken by introducing a
potential , which consists of periodically repeated cells with each cell
containing an asymmetric array of strongly localized inhomogeneities at
positions . A collective coordinate approach shows that the positions,
heights and widths of the inhomogeneities (in that order) are the crucial
parameters so as to obtain an optimal effective potential that yields
a maximal average soliton velocity. essentially exhibits two
features: double peaks consisting of a positive and a negative peak, and long
flat regions between the double peaks. Such a potential can be obtained by
choosing inhomogeneities with opposite signs (e.g., microresistors and
microshorts in the case of long Josephson junctions) that are positioned close
to each other, while the distance between each peak pair is rather large. These
results of the collective variables theory are confirmed by full simulations
for the inhomogeneous sine-Gordon system
Anisotropic thermal expansion and magnetostriction of YNiBC single crystals
We present results of anisotropic thermal expansion and low temperature
magnetostriction measurements on YNiBC single crystals grown by high
temperature flux and floating zone techniques. Quantum oscillations of
magnetostriction were observed at low temperatures for starting at
fields significantly below (). Large irreversible,
longitudinal magnetostriction was seen in both, in-plane and along the c-axis,
directions of the applied magnetic field in the intermediate superconducting
state. Anisotropic uniaxial pressure dependencies of were evaluated using
results of zero field, thermal expansion measurements
Investigating the evolution of the dual AGN system ESO~509-IG066
We analyze the evolution of the dual AGN in ESO 509-IG066, a galaxy pair
located at z=0.034 whose nuclei are separated by 11 kpc. Previous observations
with XMM-Newton on this dual AGN found evidence for two moderately obscured
( cm) X-ray luminous ( erg/s) nuclear
sources. We present an analysis of subsequent Chandra, NuSTAR and Swift/XRT
observations that show one source has dropped in flux by a factor of 10 between
2004 and 2011, which could be explained by either an increase in the absorbing
column or an intrinsic fading of the central engine possibly due to a decrease
in mass accretion. Both of these scenarios are predicted by galaxy merger
simulations. The source which has dropped in flux is not detected by NuSTAR,
which argues against absorption, unless it is extreme. However, new Keck/LRIS
optical spectroscopy reveals a previously unreported broad H-alpha line which
is highly unlikely to be visible under the extreme absorption scenario. We
therefore conclude that the black hole in this nucleus has undergone a dramatic
drop in accretion rate. From AO-assisted near-infrared integral-field
spectroscopy of the other nucleus, we find evidence that the galaxy merger is
having a direct effect on the kinematics of the gas close to the nucleus of the
galaxy, providing a direct observational link between the galaxy merger and the
mass accretion rate on to the black hole.Comment: Accepted for publication in Ap
The Central Molecular Gas Structure in LINERs with Low-Luminosity Active Galactic Nuclei: Evidence for Gradual Disappearance of the Torus
We present observations of the molecular gas in the nuclear environment of three prototypical low-luminosity active galactic nuclei (LLAGNs), based on VLT/SINFONI AO-assisted integral-field spectroscopy of H2 1-0 S(1) emission at angular resolutions of ~0.\u27\u2717. On scales of 50-150 pc, the spatial distribution and kinematics of the molecular gas are consistent with a rotating thin disk, where the ratio of rotation (V) to dispersion (σ) exceeds unity. However, in the central 50 pc, the observations reveal a geometrically and optically thick structure of molecular gas (V/σ \u3c 1 and N H \u3e 1023 cm–2) that is likely to be associated with the outer extent of any smaller scale obscuring structure. In contrast to Seyfert galaxies, the molecular gas in LLAGNs has a V/σ \u3c 1 over an area that is ~9 times smaller and column densities that are on average ~3 times smaller. We interpret these results as evidence for a gradual disappearance of the nuclear obscuring structure. While a disk wind may not be able to maintain a thick rotating structure at these luminosities, inflow of material into the nuclear region could provide sufficient energy to sustain it. In this context, LLAGNs may represent the final phase of accretion in current theories of torus evolution. While the inflow rate is considerable during the Seyfert phase, it is slowly decreasing, and the collisional disk is gradually transitioning to become geometrically thin. Furthermore, the nuclear region of these LLAGNs is dominated by intermediate-age/old stellar populations (with little or no ongoing star formation), consistent with a late stage of evolution
The Nature of Active Galactic Nuclei with Velocity Offset Emission Lines
We obtained Keck/OSIRIS near-IR adaptive optics-assisted integral-field spectroscopy to probe the morphology and kinematics of the ionized gas in four velocity-offset active galactic nuclei (AGNs) from the Sloan Digital Sky Survey. These objects possess optical emission lines that are offset in velocity from systemic as measured from stellar absorption features. At a resolution of ~0".18, OSIRIS allows us to distinguish which velocity offset emission lines are produced by the motion of an AGN in a dual supermassive black hole system, and which are produced by outflows or other kinematic structures. In three galaxies, J1018+2941, J1055+1520, and J1346+5228, the spectral offset of the emission lines is caused by AGN-driven outflows. In the remaining galaxy, J1117+6140, a counterrotating nuclear disk is observed that contains the peak of Paα emission 0".2 from the center of the galaxy. The most plausible explanation for the origin of this spatially and kinematically offset peak is that it is a region of enhanced Paα emission located at the intersection zone between the nuclear disk and the bar of the galaxy. In all four objects, the peak of ionized gas emission is not spatially coincident with the center of the galaxy as traced by the peak of the near-IR continuum emission. The peaks of ionized gas emission are spatially offset from the galaxy centers by 0".1–0".4 (0.1–0.7 kpc). We find that the velocity offset originates at the location of this peak of emission, and the value of the offset can be directly measured in the velocity maps. The emission-line ratios of these four velocity-offset AGNs can be reproduced only with a mixture of shocks and AGN photoionization. Shocks provide a natural explanation for the origin of the spatially and spectrally offset peaks of ionized gas emission in these galaxies
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