6,360 research outputs found
Infrared 3D Observations of Nearby Active Galaxies
We present multi-wavelength imaging observations of three nearby and famous
active galaxies obtained with NICMOS, ISOCAM and the MPE near-IR integral field
spectrometer. The data reveal a variety of features and properties that are
missed in optical studies and in traditional IR monodimensional spectroscopy.Comment: 6 pages, to appear in "Imaging the Universe in Three Dimensions:
Astrophysics with Advanced Multi-Wavelength Imaging Devices", eds. W. van
Breugel and J. Bland-Hawthorn, needs pasp3D.st
Generation of isolated attosecond pulses in the far field by spatial filtering with an intense few-cycle mid-infrared laser
We report theoretical calculations of high-order harmonic generation (HHG) of
Xe with the inclusion of multi-electron effects and macroscopic propagation of
the fundamental and harmonic fields in an ionizing medium. By using the
time-frequency analysis we show that the reshaping of the fundamental laser
field is responsible for the continuum structure in the HHG spectra. We further
suggest a method for obtaining an isolated attosecond pulse (IAP) by using a
filter centered on axis to select the harmonics in the far field with different
divergence. We also discuss the carrier-envelope-phase dependence of an IAP and
the possibility to optimize the yield of the IAP. With the intense few-cycle
mid-infrared lasers, this offers a possible method for generating isolated
attosecond pulses.Comment: 8 figure
The fractional Keller-Segel model
The Keller-Segel model is a system of partial differential equations
modelling chemotactic aggregation in cellular systems. This model has blowing
up solutions for large enough initial conditions in dimensions d >= 2, but all
the solutions are regular in one dimension; a mathematical fact that crucially
affects the patterns that can form in the biological system. One of the
strongest assumptions of the Keller-Segel model is the diffusive character of
the cellular motion, known to be false in many situations. We extend this model
to such situations in which the cellular dispersal is better modelled by a
fractional operator. We analyze this fractional Keller-Segel model and find
that all solutions are again globally bounded in time in one dimension. This
fact shows the robustness of the main biological conclusions obtained from the
Keller-Segel model
Disentangling the spatial substructure of Cygnus OB2 from Gaia DR2
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietyFor the first time, we have explored the spatial substructure of the Cygnus OB2 association using parallaxes from the recent second Gaia data release. We find significant line-of-sight substructure within the association, which we quantify using a parametrized model that reproduces the observed parallax distribution. This inference approach is necessary due to the non-linearity of the parallax distance transformation and the asymmetry of the resulting probability distribution. Using a Markov Chain Monte Carlo ensemble sampler and an unbinned maximum likelihood test, we identify two different stellar groups superposed on the association. We find the main Cygnus OB2 group at ∼1760 pc, further away than recent estimates have envisaged, and a foreground group at ∼1350 pc. We also calculate individual membership probabilities and identify outliers as possible non-members of the association.Peer reviewe
Interaction-Induced Quantum Dephasing in Mesoscopic Rings
Combining nonperturbative techniques with Monte Carlo simulations we
demonstrate that quantum coherence effects for a particle on a ring are
suppressed beyond a finite length even at zero temperature if the
particle is coupled to a diffusive electron gas by means of long range Coulomb
interaction. This length is consistent with derived from
weak-localization-type of analysis.Comment: 4 revtex pages, 2 figure
Infrared Observations of AGN
We present results from an imaging and spectroscopic study of the dust
properties of Seyfert galaxies in the 1-10um range. The data are compared to
state of the art models of torus emission to constrain geometrical and physical
properties of the obscuring medium.Comment: 2 pages, to appear in the IAU Symp.No.222 proceedings:"The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei", Gramado, Brazil, March
1-5, 200
The Multitude of Unresolved Continuum Sources at 1.6 microns in Hubble Space Telescope images of Seyfert Galaxies
We examine 112 Seyfert galaxies observed by the Hubble Space Telescope (HST)
at 1.6 microns. We find that ~50% of the Seyfert 2.0 galaxies which are part of
the Revised Shapeley-Ames (RSA) Catalog or the CfA redshift sample contain
unresolved continuum sources at 1.6 microns. All but a couple of the Seyfert
1.0-1.9 galaxies display unresolved continuum sources. The unresolved sources
have fluxes of order a mJy, near-infrared luminosities of order 10^41 erg/s and
absolute magnitudes M_H ~-16. Comparison non-Seyfert galaxies from the RSA
Catalog display significantly fewer (~20%), somewhat lower luminosity nuclear
sources, which could be due to compact star clusters. We find that the
luminosities of the unresolved Seyfert 1.0-1.9 sources at 1.6 microns are
correlated with [OIII] 5007A and hard X-ray luminosities, implying that these
sources are non-stellar. Assuming a spectral energy distribution similar to
that of a Seyfert 2 galaxy, we estimate that a few percent of local spiral
galaxies contain black holes emitting as Seyferts at a moderate fraction, 10^-1
to 10^-4, of their Eddington luminosities. With increasing Seyfert type the
fraction of unresolved sources detected at 1.6 microns and the ratio of 1.6
microns to [OIII] fluxes tend to decrease. These trends are consistent with the
unification model for Seyfert 1 and 2 galaxies.Comment: accepted by Ap
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