17,776 research outputs found
Stellar population gradients in Seyfert 2 galaxies. Northern sample
We use high signal-to-noise ratio long-slit spectra in the 3600-4700A range
of the twenty brightest northern Seyfert 2 galaxies to study the variation of
the stellar population properties as a function of distance from the nucleus.
In order to characterize the stellar population and other continuum sources
(e.g. featureless continuum FC) we have measured equivalent widths Ws of six
absorption features, four continuum colours and their radial variations, and
performed spectral population synthesis as a function of distance from the
nucleus. About half the sample has CaIIK and G-band W values smaller at the
nucleus than at 1 kpc from it, due to a younger population and/or FC. The
stellar population synthesis shows that, while at the nucleus, 75% of the
galaxies present contribution > 20% of ages younger or equal than 100Myr and/or
of a FC, this proportion decreases to 45% at 3 kpc. In particular, 55% of the
galaxies have contribution > 10% of the 3 Myr/FC component (a degenerate
component in which one cannot separate what is due to a FC or to a 3 Myr
stellar population) at the nucleus, but only 25% of them have this contribution
at 3 kpc. As reference, the stellar population of 10 non-Seyfert galaxies,
spanning the Hubble types of the Seyfert (from S0 to Sc) was also studied. A
comparison between the stellar population of the Seyferts and that of the
non-Seyferts shows systematic differences: the contribution of ages younger
than 1 Gyr is in most cases larger in the Seyfert galaxies than in
non-Seyferts, not only at the nucleus but up to 1 kpc from it.Comment: 23 pages, 18 figures, MNRAS in pres
The coastal team at Flanders Hydraulics Research: matching research priorities and CZM needs for the 21st century
An atlas of Calcium triplet spectra of active galaxies
We present a spectroscopic atlas of active galactic nuclei covering the
region around the 8498, 8542, 8662 Calcium triplet (CaT) lines. The sample
comprises 78 objects, divided into 43 Seyfert 2s, 26 Seyfert 1s, 3 Starburst
and 6 normal galaxies. The spectra pertain to the inner ~300 pc in radius, and
thus sample the central kinematics and stellar populations of active galaxies.
The data are used to measure stellar velocity dispersions (sigma_star) both
with cross-correlation and direct fitting methods. These measurements are found
to be in good agreement with each-other and with those in previous studies for
objects in common. The CaT equivalent width is also measured. We find average
values and sample dispersions of W_CaT of 4.6+/-2.0, 7.0 and 7.7+/-1.0
angstrons for Seyfert 1s, Seyfert 2s and normal galaxies, respectively. We
further present an atlas of [SIII]\lambda 9069 emission line profiles for a
subset of 40 galaxies. These data are analyzed in a companion paper which
addresses the connection between stellar and Narrow Line Region kinematics, the
behaviour of the CaT equivalent width as a function of sigma_star, activity
type and stellar population properties.Comment: 18 pages, 10 figures, accepted for publication in MNRA
On the nature of the near-UV extended light in Seyfert galaxies
We study the nature of the extended near-UV emission in the inner kiloparsec
of a sample of 15 Seyfert galaxies which have both near-UV (F330W) and narrow
band [OIII] high resolution Hubble images. For the majority of the objects we
find a very similar morphology in both bands. From the [OIII] images we
construct synthetic images of the nebular continuum plus the emission line
contribution expected through the F330W filter, which can be subtracted from
the F330W images. We find that the emission of the ionised gas dominates the
near-UV extended emission in half of the objects. A further broad band
photometric study, in the bands F330W (U), F547M (V) and F160W (H), shows that
the remaining emission is dominated by the underlying galactic bulge
contribution. We also find a blue component whose nature is not clear in 4 out
of 15 objects. This component may be attributed to scattered light from the
AGN, to a young stellar population in unresolved star clusters, or to
early-disrupted clusters. Star forming regions and/or bright off-nuclear star
clusters are observed in 4/15 galaxies of the sample.Comment: 23 pages, 6 figures, 3 tables; accepted for publication in MNRA
Morfologische trends op middellange termijn van strand, vooroever en kustnabije zone langsheen de Belgische kust: deelrapport in het kader van het Quest4Dproject
Evaluation of a shoreface nourishment in De Haan: analysis of 20 years of data
In the framework of the implementation of the Master Plan for Coastal Safety and Vlaamse Baaien project, an assessment of the added value of shoreface nourishment as coastal protection measure and as alternative to classic procedures for beach nourishment maintenance will be performed. This project, entitled “Shoreface nourishments as coastal protection measure”, is carried out at Flanders Hydraulics Research with as central activity the monitoring of a pilot shoreface nourishment that will take place in 2013 in Mariakerke.The only antecedent of a shoreface nourishment in Belgium is the nourishment performed in De Haan in 1990. This document brings together results from the monitoring carried out in the 90’s as well as new results obtained from later surveys in the study area. The results is a more than twenty years analysis of the morphological evolution of the coast at the Haan. The interpretation of the results is not straight forward due to the various nourishments performed since then in neighboring areas. However, it is possible to conclude that after a local cross-and long-shore redistribution of the sand nourished in the shoreface, this sand has not been transported and therefore has remain in the system acting as sand supply for the beach.A general reduction of the background erosion has also been detected during this analysis but the fact that during the study period no severe storms occurred makes it difficult to draw a definitive conclusion in this regard.Taking into account the difficulties encountered to draw conclusions on the evolution of the beach and shoreface in De Haan during this study and the goals of the new project it is recommended that during the monitoring of the pilot shoreface nourishment to be started in 2013 no other nourishments on the beach and/or neighboring shoreface and beaches are executed
Density Matrix and Renormalization for Classical Lattice Models
We review the variational principle in the density matrix renormalization
group (DMRG) method, which maximizes an approximate partition function within a
restricted degrees of freedom; at zero temperature, DMRG mini- mizes the ground
state energy. The variational principle is applied to two-dimensional (2D)
classical lattice models, where the density matrix is expressed as a product of
corner transfer matrices. (CTMs) DMRG related fields and future directions of
DMRG are briefly discussed.Comment: 21 pages, Latex, 14 figures in postscript files, Proc. of the 1996 El
Escorial Summer School on "Strongly Correlated Magnetic and Superconducting
Systems
Black hole evaporation with separated fermions
In models with a low quantum gravity scale, a well-motivated reason to expect
quark and lepton fields are localized but physically separated is to avoid
proton decay. This could happen in a ``fat-brane'' or in an additional,
orthogonal 1/TeV sized dimension in which the gauge and Higgs fields live
throughout. Black holes with masses of order the quantum gravity scale are
therefore expected to evaporate non-universally, preferentially radiating
directly into quarks or leptons but not both. Should black holes be copiously
produced at a future hadron collider, we find the ratio of final state jets to
charged leptons to photons is 113:8:1, which differs from previous analyses
that assumed all standard model fields live at the same point in the extra
dimensional space.Comment: 5 pages, REVTe
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